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* Premise of the study: Species in the aquatic genus Nymphoides have inflorescences that appear to arise from the petioles of floating leaves. The inflorescence-floating leaf complex can produce vegetative propagules and/or additional inflorescences and leaves. We analyzed the morphology of N. aquatica to determine how this complex relates to whole plant architecture and whether whole plant growth is sympodial or monopodial. * Methods: We used dissections, measurements, and microscopic observations of field-collected plants and plants cultivated for 2 years in outdoor tanks in south Florida, USA. * Key results: Nymphoides aquatica had a submerged plagiotropic rhizome that produced floating leaves in an alternate/spiral phyllotaxy. Rhizomes were composed of successive sympodial units that varied in the number of leaves produced before the apex terminated. The basic sympodial unit had a prophyll that subtended a renewal-shoot bud, a short-petioled leaf (SPL) with floating lamina, and an inflorescence; the SPL axillary bud expanded as a vegetative propagule. Plants produced either successive basic sympodial units or expanded sympodia that intercalated long-petioled leaves between the prophyll and the SPL. * Conclusions: Nymphoides aquatica grows sympodially, forming a rhizome composed of successive basic sympodia and expanded sympodial units. Variations on these types of sympodial growth help explain the branching patterns and leaf morphologies described for other Nymphoides species. Monitoring how these two sympodial phases are affected by water depth provides an ecologically meaningful way to assess N. aquatica's responses to altered hydrology. Key words: aquatic plant; clonal propagation; Everglades; heterophylly; leaf dimorphism; prophyll; slough; sympodial; vegetative reproduction. doi: 10.3732/ajb.1000242

* Premise of the study: Pyrus callervana Decne., an ornamental tree species introduced from China, is a relatively new invasive that has only recently begun to spread across the United States after intraspecific hybridization between cultivars. The function of such hybridization in the evolution of invasiveness is still relatively understudied, especially with respect to the initial establishment and persistence of invasive genotypes. Multiple introductions of genetically divergent populations or cultivars may benefit from new genetic combinations created during hybridization events and/or release from Allee effects in founder populations. * Methods: We quantified the outcome of intraspecific hybridization between cultivars of P. calleryana in a common garden. Measures of the reproductive success and establishment ability of their early- and advanced-generation hybrid offspring were collected to assess the likelihood of particular cultivar genotypes to establish in invasive populations. These traits also were compared between cultivated and invasive parents to identify any generational differences in invasive potential. * Key results: Differences were detected in measures of reproductive ability, but no group emerged as consistently more fecund. Advanced-generation hybrids also had significantly less biomass, indicating a reduction in hybrid performance relative to that of the cultivated progeny. * Conclusion: Ultimately, this study indicates that increased spread of P. calleryana has been initiated by introduction of multiple cultivar types and subsequent widespread planting and is not the result of an inherent fitness advantage of hybrid progeny. Key words: cultivation; intraspecific hybridization; invasive; propagule pressure; Pyrus calleryana. doi: 10.3732/ajb.1000113

* Premise of the study: The evolution of asexual seed production (apomixis) from sexual relatives is a great enigma of plant biology. The genus Boechera is ideal for studying apomixis because of its close relation to Arabidopsis and the occurrence of sexual and apomictic species at low ploidy levels (diploid and triploid). Apomixis is characterized by three components: unreduced embryo-sac formation (apomeiosis), fertilization-independent embryogenesis (parthenogenesis), and functional endosperm formation (pseudogamy or autonomous endosperm formation). Understanding the variation in these traits within and between species has been hindered by the laborious histological analyses required to analyze large numbers of samples. * Methods: To quantify variability for the different components of apomictic seed development, we developed a high-throughput flow cytomelric seed screen technique to measure embryo: endosperm ploidy in over 22000 single seeds derived from 71 accessions of diploid and triploid Boechera. * Key results: Three interrelated features were identified within and among Boechera species: (1) variation for most traits associated with apomictic seed formation, (2) three levels of apomeiosis expression (low, high, obligate), and (3) correlations between apomeiosis and parthenogenesis/pseudogamy. * Conclusions: The data presented here provide a framework for choosing specific genotypes for correlations with large 'omics' data sets being collected for Boechera to study population structure, gene flow, and evolution of specific traits. We hypothesize that low levels of apomeiosis represent an ancestral condition of Boechera, whereas high apomeiosis levels may have been induced by global gene regulatory changes associated with hybridization. Key words: apomeiosis; apomixis; Boechera; embryo; endosperm; flow cytometry; parthenogenesis; pseudogamy. doi: 10.3732/ajb.1000188

* Premise of the study: Habitat fragmentation is often assumed to result in limited genetic diversity across impacted plant communities. Central Florida has undergone extensive anthropogenic changes, while also harboring large numbers of endemic species. In this study, we assessed genetic structure and dependence on clonality in a central Florida endemic, Illicium parviflorum (Illiciaceae), as well as evaluated genetic diversity of this species in horticultural stocks. * Methods: Six sites were sampled across the geographic range of I. parviflorum. A PCR-based assay using intersimple sequence repeats (ISSRs) was used to assess genetic structure. * Key results: Results, based on 26 ISSR loci, suggest that clonal structure plays a role in all populations, with PD values ranging from 0.25 to 0.50. Only two populations exhibited unique genotypes, while the remaining four populations shared genotypes. Horticultural samples all shared one genotype, which can be traced back to a single natural population. * Conclusions: Clonal reproduction is an important factor in the maintenance of natural populations of I. parviflorum, although the degree to which this is true varies by population. Horticultural samples likely represent a single or very few collection events, indicating the need for greater genetic diversity within horticultural stocks. Further analyses using microsatellites are planned to confirm these results. doi: 10.3732/ajb.0900291

* Premise of the study: Flowering plants that rely on pollinators for most of their reproduction may experience unpredictable and inconsistent availability of effective pollinators throughout their reproductive lifetime. We investigated the reproductive ecology of two subspecies of the tufted evening primrose, Oenothera cespitosa, which occupy geographically and edaphically distinct habitats in western North America: O. cespitosa subsp, navajoensis inhabits sandstone soils on open sites or rocky slopes in the Colorado Plateau and O. cespitosa subsp, cespitosa grows in clay soils on talus slopes and exposed rocky ridges in the western Great Plains and northern Rocky Mountains of the United States. * Methods: Pollen augmentation and selfing experiments, floral visitor observations, and single-visit effectiveness experiments were conducted over 4 years to examine the breeding system and spatiotemporal variation in pollinator behavior, assemblage, and abundance at different populations for each subspecies. * Key results: Both subspecies of O. cespitosa were self-incompatible and pollen-limited, suggesting that the relative abundance, effectiveness, and movement patterns of different insects as pollinators influenced the quality and quantity of seed production in these plants. Medium-sized vespertine hawkmoths (Hyles lineata, Sphinx vashti) were effective pollinators when present, as were large matinal bees (Anthophora affabilis, A. dammersi, Xylocopa tabaniformis androleuca), whereas small oligolectic Lasioglossum bees primarily functioned as pollen thieves in the evening and morning. * Conclusions: These findings highlight the importance of variability of pollinator composition and abundance in the evolution of plant breeding systems and reproductive success at varying spatial and temporal scales. Key words: bees; breeding system; hawkmoths; Oenothera cespitosa; Onagraceae; plant reproductive success; pollination; spatiotemporal variation. doi: 10.3732/ajb.1000086

* Premise of the study: Current reproduction in polycarpic plants may be affected by a wide variety of factors, including carryover or 'historical' effects derived from environments experienced early in life and from previous investments in organ preformation or other life functions, such as growth or reproduction. Historical effects as determinants of plant reproductive success in a specific season have received considerably less attention than events during the current reproductive episode, especially for short-lived plants. * Methods: We used structural equation modeling to assess direct and indirect relations between past reproduction and both subsequent reproduction and growth in Helianthemum squamatum, a short-lived polycarpic plant. Additionally, we explored the effects of current reproduction on future survival (binomial variable) by using logistic regression. * Key results: Historical effects derived from previous growth positively affected current reproduction, suggesting the existence of a reproductive hierarchy in the population, in which some individuals are consistently better growers and seeders. The lack of effects of current reproduction on future reproduction, together with the existence of a negative effect on future survival, suggests that to invest maximally in reproduction at the expense of a short life span may be the optimal strategy for H. squamatum, a species inhabiting very unpredictable ecosystems. * Conclusions: Historical effects derived from past investments in growth or reproduction may have important consequences for current plant performance and may play an essential role in shaping life histories. Key words: Cistaceae; Helianthemum squamatum; Mediterranean; reproductive hierarchy; reproductive lifetime; semiarid; structural equation modeling. doi: 10.3732/ajb.1000072

Premise of the study: The study of geographic variation in ecologically important traits within and among taxa is a first step toward understanding the environmental factors that contribute to population differentiation and species divergence. This study examines variation in mean sex allocation per flower (androecium mass/gynoecium mass) among 49 wild populations representing 12 Pedicularis species across an elevation gradient on the eastern Tibetan Plateau. Methods: We used population means to evaluate sources of variation in per-flower sex allocation within and across species. In particular, we evaluate the relative influence of intrinsic (i.e., plant size, estimated as aboveground stem biomass) vs. extrinsic factors affecting mean sex allocation among populations. Key results: Mean sex allocation per flower (the relative investment in male floral organs) is negatively correlated with mean plant size; populations of large plants produce relatively female-biased flowers. This relationship between mean plant size and mean sex allocation is not statistically significant, however, when the effect of elevation is controlled statistically. Among populations within and across species, mean sex allocation increases with elevation. This relationship persists even when the effect of mean plant size is controlled statistically. Factors associated with increasing elevation appear to favor genotypes and/ or taxa with male-biased flowers. Conclusion: Extrinsic environmental conditions may be more important than intrinsic resource status in determining patterns of geographic variation in mean sex allocation among populations or species of Pedicularis. We cannot conclude whether the effect of elevation on mean sex allocation is the result of environmentally induced plasticity, genetically based adaptation, or species sorting, but it is only partly mediated by mean plant size. Key words: elevation; geographic variation; Orobanchaceae; Pedicularis; population differentiation; sex allocation. doi: 10.3732/ajb.0900301

* Premise of the study: Embryonic inbreeding depression is a key influence on mating system evolution and can be difficult to estimate in self-incompatible species. A pollen chase experiment was used to estimate the magnitude of embryonic inbreeding depression in Costa Rican Witheringia solanacea, a species polymorphic for self-incompatibility (SI). In a pollen chase experiment, bud self-pollinations are followed after anthesis by outcross pollinations, with a comparable pair of outcross pollinations used as a control. Lowered seed set for the self-precedence treatment indicates embryonic inbreeding depression. * Methods: Embryonic inbreeding depression was assayed for self-compatible (SC) individuals and for SI plants from two populations that differ quantitatively in the onset and enzymatic activity of their SI response. Microsatellite markers were used to assay the selfing rate of a sample of surviving progeny from the prior self-pollination treatment. * Key results: SC individuals showed no evidence of embryonic inbreeding depression. In SI plants, prior self- pollination reduced seed number by 28-70%, depending on population. Microsatellite genotyping revealed that embryonic inbreeding depression was even more severe than estimated by the phenotypic data: for mature fruits resulting from self- pollination precedence, the majority of the progeny were the result of outcross fertilization. * Conclusions: Lineage-specific purging of recessive lethals has accompanied the evolution of SC in this species. SI populations show contrasting levels of embryonic inbreeding depression, with nearly complete embryonic lethality upon selfing in the Monteverde population. In the lace of high embryonic inbreeding depression, an increase in selling rate can evidently occur only under severe pollen limitation. Key words: Costa Rica: embryonic inbreeding depression; evolution; mating system: self-compatibility: self- incompatibility; Solanaceae; Witheringia solanacea. doi: 10.3732/ajb.1000020

* Premise of the study: A mixture of outcrossing and selfing is often observed in plant populations. Although mixed mating is ubiquitous, it has several potential evolutionary explanations. Mixed mating may be actively maintained by selection, passively determined by the pollination environment, or a transitional stage during the evolution of self-fertilization. * Methods: We studied patterns of self-compatibility and selfing rates in a population of Leavenworthia alubamica that recently lost self-incompatibility. We also experimentally tested whether natural selection against selfing at the pre-or postzygotic stage is sufficient to explain mixed mating in this population. * Key results: Visualizing pollen tube growth following self-pollination, we found that nearly all plants were fully self-compatible. Progeny array analysis revealed that the average selfing rate of the population was s = 0.523. The inbreeding coefficient in the parents (F = 0.539) exceeded the amount expected if the selfing rate (s) were constant [[F.sub.cq] = s/(2 - s)l, indicating either population subdivision or higher selfing rates in the past. Inference of family-level selfing rates revealed substantial variation. Experiments found that self and outcross pollen fertilized nearly equal numbers of ovules in competition. Comparison of seed production following self-or cross-pollination failed to implicate early acting inbreeding depression as a factor maintaining mixed mating. * Conclusions: The results of our experiments suggest that mixed mating is not maintained by selection against self- pollen or zygotes in this population. Mixed mating is most likely a byproduct of the pollination process but may also be a transitional stage during the evolution of higher selfing rates. Key words: bet hedging; Brassicaceae; fluctuating environments; inbreeding depression; Leavenworthia alubamica; mating system; pollen competition; reproductive assurance. doi: 10.3732/ajb.1000032

The reproductive system is one of the key mechanisms that determine genetic diversity at different biological levels. However, few attempts have been made to assess the consequences of asexual reproduction by comparing genetic structure and fecundity of seed families in asexually and sexually reproducing individuals. We have examined two similar hawthorn species, Crataegus crusgalli and C. punctata, that differ in ploidy level and breeding system. Fecundity (per-fruit seed set) and microsatellite genotypes for five loci were determined in 18 and 26 seed families of C. crus-galli and C. punctata (totals of 83 and 118 embryos), respectively. Compared with the sexual diploid C. punctata, tetraploid C. crus-galli shows similar fecundity, but lower genotypic diversity within and between seed families. Reproduction in the tetraploid, while predominantly apomictic, is nevertheless accompanied by outcrossing and selfing. We conclude that in C. crus-galli pollen flow between conspecific individuals is limited, and the combination of pollen fertility, self-compatibility, and pseudogamous apomixis provides reproductive assurance in these tetraploids. Reproductive assurance, in turn, may explain the derived floral architecture seen in most North American tetraploid hawthorns. We also discuss analytical approaches for inferring mating-system parameters in tetraploids and for comparing microsatellite variation across ploidy levels. Key words: Apomixis; family genetic structure; fecundity; embryo genotypes; microsatellite; outcrossing; pollen flow; polyploidy; progeny array; Rosaceae. doi: 10.3732/ajb.0900091

Viability of long-distance pollen links ecological models to the genetic structure of forest tree populations, determining how forests will adapt to climate change and how far genes flow from genetically modified (GM) pine plantations. Addressing this landscape-scale inquiry is feasible when the pollen source, the delivery system, and the receiver field can be made explicit. To this end, I measured long-distance pollen germination along a 160-km transect along the North Carolina coastline, including 45 000 ha of mature Pinus taeda plantations and barrier islands. Using this system, I tested three hypotheses: (1) pine pollen germinates 'after dispersal on meso-scale distances, (2) sodium chloride exposure reduces germination of pollen captured over open saltwater, and (3) viable pine pollen is present at high altitudes before local peak pollen shed. The experimental findings are as follows: pine pollen had germination rates of 2 to 57% after dispersal at distances from 3 to 41 kin, sodium chloride solutions mildly reduced P taeda pollen germination, and viable pine pollen grains were captured at an altitude of 610 m. GM pine plantings thus have a potential to disperse viable pollen at least 41 km from the source. Wind and rainfall, as integral parts of regional atmospheric systems, together exert a powerful influence on the genetic structure of forest tree populations. Key words: aerosols; climate change; conifer reproductive biology; genetically modified (GM) forest trees; heterospory; long-distance dispersal; male gametophyte; North Carolina; Pinaceae; Pinus taeda; U.S. Forest Health Initiative. doi: 10.3732/ajb.0900255

Reproductive barriers play a major role in the origin and maintenance of biodiversity by restricting gene flow between species. Although both pre- and postzygotic barriers often isolate species, prezygotic barriers are thought to contribute more to reproductive isolation. We investigated possible reproductive barriers between Leavenworthia alabamica and L. crassa, parapatric species with high morphological and ecological similarity and the ability to hybridize. Using greenhouse and field experiments, we tested for habitat isolation and genetic incompatibilities. From controlled crosses, we identified unilateral incompatibility (a partial prezygotic barrier associated with the self-incompatibility system), but no evidence of other genetic incompatibilities. We found a small reduction in pollen viability of F1 hybrids and early germination of [F.sub.1], [F.sub.2], and BC hybrids relative to L. alabamica and L. crassa in a common garden experiment, but the effect on fitness was not tested. Field studies of hybrid pollen viability and germination are needed to determine if they contribute to reproductive isolation. In a reciprocal transplant, we found no evidence of habitat isolation or reduced hybrid survival (from seedling to adult stage) or reproduction. These data suggest unilateral incompatibility partially reproductively isolates L. alabamica and L. crassa, but no other reproductive barriers could be detected. Key words: Brassicaceae; genetic incompatibilities; hybrid fitness; habitat isolation; Leavenworthia alabamica; Leavenworthia crassa; reproductive barriers; unilateral incompatibility. doi: 10.3732/ajb.0900184

This paper explores the relative impacts of reduction and polymerization on the evolution of reproductive structures in the small but morphologically diverse family Centrolepidaceae. Centrolepidaceae are closely related to Restionaceae and belong to the large order Poales, which also includes the grasses. In the largest genus of Centrolepidaceae, Centrolepis, the reproductive structures are viewed either as highly unusual aggregations of reduced flowers (the pseudanthial interpretation) or as unique flowers evolved through extreme reduction in the androecium, usually accompanied by a drastic increase in carpel number and elaboration of the entire gynoecium. Comparative data are here presented on gynoecia of all three genera of Centrolepidaceae; these data strongly support the latter (euanthial) interpretation. The combined phenomenon of carpel multiplication and decrease in stamen number is unexpected in a predominantly wind-pollinated lineage. Applying a pseudanthial interpretation would create a considerable morphological gap with reproductive structures of other Poales, whereas accepting a euanthial concept allows an almost continuous morphological series with related taxa. Key words: anatomy; Centrolepidaceae; development; flower; gynoecium; inflorescence; morphology; pseudanthium; Poales. doi: 10.3732/ajb.0900074

The cost of sexual reproduction is incurred when the current reproductive episode contributes to a a decline in future plant performance. To test the hypotheses that a trade-off exists between current sexual reproduction and subsequent clonal regeneration and that resources limit reproduction and regeneration, plants of the widespread moss Pterygoneurum ovatum were subjected to induced sporophytic abortion, upper leaf removal, and nutrient amendment treatments. Sexually reproducing plants were slower or less likely to produce regenerative structures (protonemata or shoots) and produced fewer regenerative tissue areas or structures. The ability and the timeline to reproduce sexually and regenerate clonally were unaffected by an inorganic nutrient amendment. However, when leaves subtending the sporophyte were removed, the sporophytes were less likely to mature, tended to take a longer time to mature, and were smaller compared to sporophytes from shoots with a full complement of upper leaves. Our findings indicate that plants investing in sexual reproduction suffer a cost of decreased clonal regeneration and indicate that sporophyte maturation is resource-limited, with upper leaves contributing to the nutrition of the sporophyte. This study represents only the second explicit experimental demonstration of a trade-off between sexual and asexual reproduction in bryophytes. Key words: abortion; bryophyte; Pottiaceae; protonema; Pterygoneurum ovatum; regeneration; sexual reproduction; sporophyte; trade-offs. doi: 10.3732/ajb.0900084

Studies of mycoheterotrophs, defined as plants that obtain carbon resources from associated mycorrhizal fungi, have fundamentally contributed to our understanding of the importance and complexity of symbiotic ecological interactions. However, to date, the reproductive ecology of these organisms remains empirically understudied, with existing literature presenting hypotheses about traits including a generalist pollination syndrome and autogamous self-pollination. To address this gap in our knowledge of the reproductive ecology of mycoheterotrophic plants, we comparatively analyzed three species of two monotropoid genera, Monotropa and Monotropsis. During three consecutive years of field observations and manipulations of four populations of Monotropa uniflora, seven of M. hypopitys (both red and yellow color forms), and two of Monotropsis odorata, we investigated flowering phenology, pollination ecology, breeding system, floral herbivory, and reproductive effort and output. Contrary to previous predictions, our results revealed that taxa are largely outcross-pollinated and specialized toward Bombus pollinators. Additionally, species differ in breeding system, timing and duration of reproductive development, fluctuations in reproductive effort and output, and fitness impacts of herbivory. This study is the first thorough investigation of the reproductive ecology of mycoheterotrophic species and provides insight into possible limitations in reproductive traits imposed by a mycoheterotrophic life history. Key words: breeding system; Ericaceae; Monotropa; Monotropsis; mycoheterotroph; phenology; pollination; reproductive ecology. doi: 10.3732/ajb.0800319

The number of ovules per flower varies over several orders of magnitude among angiosperms. Here we consider evidence that stochastic uncertainty in pollen receipt and ovule fertilization has been a selective factor in the evolution of ovule number per flower. We hypothesize that stochastic variation in floral mating success creates an advantage to producing many ovules per flower because a plant will often gain more fitness from occasional abundant seed production in randomly successful flowers than it loses in resource commitment to less successful flowers. Greater statistical dispersion in pollination and fertilization among flowers increases the frequency of windfall success, which should increase the strength of selection for greater ovule number per flower. We therefore looked for evidence of a positive relationship between ovule number per flower and the statistical dispersion of pollen receipt or seed number per flower in a comparative analysis involving 187 angiosperm species. We found strong evidence of such a relationship. Our results support the hypothesis that unpredictable variation in mating success at the floral level has been a factor in the evolution of ovule packaging in angiosperms. Key words: bet hedging; ovule; pollination; reproductive evolution; seed set; stigmatic pollen load. doi: 10.3732/ajb.0800183

Opuntia robusta has hermaphroditic, dioecious, and trioecious populations. To enhance our understanding of this breeding system diversity, we compared the reproductive output of males, females, and hermaphrodites in a trioecious population using field evaluations, controlled crosses, and progeny tests. Unisexuals were fully sterile in one sex function. Hermaphrodites were fully fertile for both functions. Consistent with the sex-allocation theory, unisexuality increased the quality and quantity (in males) of the gametes of the functional sex, relative to those of hermaphrodites, probably explained by maternal and paternal effects. The increase was higher in males than in females, suggesting a more expensive female function. Theoretically, this disproportional increase is required for unisexuals to invade a hermaphroditic population with prior selfing, negligible pollen discounting, and undetectable inbreeding depression, features found in O. robusta, therefore helping to explain dioecious populations. However, in the study population, the actual seed output of females was lower and had a higher variance than that of hermaphrodites, which also reproduce through pollen. Unisexuals are unlikely to be maintained by their actual reproductive output in this pollen-limited environment. Hermaphrodites may persist in this population by producing their seeds autonomously and by reducing interspecific fertilization by prior selfing and ovule discounting. Key words: cactus; dioecy; hermaphroditism; inbreeding depression; maternal effects; ovule discounting; pollen discounting; pollen limitation: pollen--ovule ratio; prior selfing; selfing; sex allocation. doi: 10.3732/ajb.0800301

Multiple field populations of two pairs of diploid sister taxa with contrasting mating systems in the genus Clarkia (Onagraceae) were surveyed to test predictions concerning the effects of resource status, estimated as plant size, on pollen and ovule production and on the pollen:ovule (P:O) ratio of flowers. Most theoretical models of size-dependent sex allocation predict that, in outcrossing populations, larger plants should allocate more resources to female function. Lower P:O ratios in larger plants compared to smaller plants have been interpreted as supporting this prediction. In contrast, we predicted that P:O ratio should not vary with plant size in predominantly selfing plants, in which each flower contributes to reproductive success equally through male and female function. We found that, in all four taxa, both ovule and pollen production per flower usually increased significantly with plant size and that the shape of this relationship was decelerating. However, ovule production either decelerated more rapidly than or at the same rate as pollen production with plant size. Consequently,the P:O ratio increased or had no relationship with plant size. This relationship was population-specifc (not taxon-specific) and independent of the mating system. Possible explanations for the increasing maleness with plant size are discussed. Key words: Clarkia: gametophyte production; mating system; Onagraceae; pollen to ovule ratio; size-dependent sex allocation.

A remarkably diverse Lower Cretaceous (Valanginian-Hauterivian) flora at Apple Bay, Vancouver Island, preserves seed plants at an important time of floristic evolutionary transition, about the same time as the earliest flowering plant megafossils. The fossils are permineralized in carbonate concretions and include tetrahedral seeds within cupule- or carpel-like structures. These enclosing structures, composed of elongate sclerenchyma cells with spiral thickenings that grade externally to a few layers of parenchyma, are vascularized by one collateral vascular bundle and lack trichomes. They apparently broke open to release the tightly enclosed seeds by valves. Seeds are similar to those of the Triassic seed fern Petriellaea, but are about 100 million years younger and differ in size, vascularization, integumentary anatomy, seed attachment, and number of seeds/cupule. These new seeds are described as Doylea tetrahedrasperma gen. et sp. nov., tentatively assigned to Corystospermales. Inverted cupules are reminiscent of an outer angiosperm integument rather than a carpel. Like fruits, cupules opened to release seeds at maturity, thereby foretelling several aspects of angiospermy. They show that nearly total ovule enclosure, a level of organization approaching angiospermy, was achieved by advanced seed ferns during the Mesozoic. Key words: angiospermy; corystosperms; Cretaceous; cupule; Petriellaea; seed ferns.

Age and size at the first reproduction and the reproductive allocation of plants are linked to different life history strategies. Aleppo pine only reproduces through seed, and, as such, early female reproduction confers high fitness in its infertile highly fireprone habitats along the Mediterranean coast because life expectancy is short. We investigated the extent of ecotypic differentiation in female reproductive allocation and examined the relation between early female reproduction and vegetative growth. In a common-garden experiment, the threshold age and size at first female reproduction and female reproductive allocation at age seven differed significantly among Aleppo pine provenances of ecologically distinct origin. Significant correlations among reproductive features of the provenances and the ecological traits of origin were found using different analytical tools. In nonlinear models of cone counts vs. stem volume, medium-sized trees (not the largest trees) produced the highest cone yield, confirming that, at the individual level, early female reproduction is incompatible with fast vegetative growth. The contribution of founder effects and adaptation to contrasting fire regimes may be confounding factors. But considering all traits analyzed, the geographical patterns of resource allocation by Aleppo pine suggest ecotypic specialization for either resource-poor (favoring early reproduction) or resource-rich (favoring vegetative growth) habitats. Key words: age at first reproduction; cones; Mediterranean; Pinaceae; Pinus halepensis; reproductive allocation; reproductive effort; threshold size.

Secondary pollen presentation is the relocation and presentation of pollen in floral structures (termed pollen presenters) other than the anthers. These pollen presenters are often found close to the stigma and have been hypothesized to increase the accuracy of pollen transfer, although no experimental studies have been done. We examined the function of the pollen presenter and its efficiency in pollen dispersal, female fitness, and the degree of interference created by self-pollen in the shrublet Polygala vayredae, an insect-pollinated species with secondary pollen presentation. Herkogamy, a mechanism generally involved in the reduction of self-interference, was also evaluated. Significant pollen was lost (49% of total pollen) during the secondary relocation in the pollen presenter. However, pollen was exported from the pollen presenter, and subsequent pollen losses were similar to those in species with primary pollen presentation. Despite the presence of a self-incompatibility system, the numbers of developed pollen tubes as well as fruit and seed production were significantly reduced by the self-pollen interference created at the stigmatic papillae level. The extent of herkogamy correlated positively with female fitness. The secondary pollen presentation mechanism may in fact be an accurate system for pollen transport, but it may also have its costs. Further comparative studies involving species with primary and secondary pollen presentation are needed to fully understand the advantages and disadvantages of secondary pollen presentation. Key words: female fitness; herkogamy; pollen dispersal; pollen presenter; pollen relocation; Polygalaceae; self-incompatibility; self-interference.

Rosa rugosa, a vigorous ornamental shrub introduced from Asia in the 19th century, is now naturalized in coastal northeastern North America, where it occasionally grows in sympatry with the native R. blanda. To document hybridization between these species, evaluate its extent across the area of sympatry, and examine the use of morphology as a field monitoring tool, we sampled 179 individuals of parental species and putative hybrids in 13 pure and 11 mixed populations. We developed allele-specific primers to assay single nucleotide polymorphisms (SNPs) markers from one chloroplast region and four low-copy nuclear introns. Our results revealed frequent bidirectional hybridization and infrequent introgression in sympatric populations of these species. The recurrent presence of [F.sub.1] hybrids in mixed populations indicated the weakness of early-acting reproductive barriers. Morphological data were concordant with molecular data and provided additional evidence for the presence of a few backcrosses. Morphological analyses yielded diagnostic characters for identifying hybrids and monitoring the hybrid zone. Such hybridization could ultimately lead to the genetic assimilation of R. blanda in mixed populations and to the formation of invasive hybrid genotypes, a phenomenon that is of economic and ecological concern because of the increasing number of exotic species worldwide. Key words: allele-specific primers; eastern North America; hybridization; introduced species; introgression; Rosa blanda; Rosa rugosa; Rosaceae.

In animal-pollinated plants, autonomous selfing provides reproductive assurance under conditions of infrequent pollinator visits or a lack of mates, but few data are available for wind-pollinated species or species with combined insect and wind-pollination, for which it is often assumed that pollen availability does not limit reproduction. In this study, the capacity of autonomous selfing was investigated in the temperate forest herb Paris quadrifolia, and an emasculation experiment was performed under natural field conditions to investigate the contribution of autonomous selfing to total seed set across a continuous gradient of densities of flowering conspecifics. In the absence of wind or pollinators, autonomous selfing was observed through anthers approaching stigmas at the end of flowering and the capacity for autonomous pollination was about 0.34. Under natural conditions, considerable outcross pollination was observed, but the proportion of ovules successfully fertilized signifcantly decreased with decreasing density of conspecifics when flowers were emasculated, but not when flowers were left intact. These results indicate that autonomous selfing resulted in reproductive assurance (RA = 0.16) and thus support the hypothesis that autonomous selfing can also provide reproductive assurance in wind-pollinated species. Key words: autogamy; delayed selfing; mixed mating; Paris quadrifolia.

Floral sex allocation at the individual and first-order branch levels and the relation between these levels were examined in Betula platyphylla var. japonica, a wind-pollinated monoecious tree. Floral sex allocation at the individual level varied with resource availability in a pattern similar to that predicted by the Masaka and Takada model (Journal of Theoretical Biology 240: 114-125). Thus, individual trees with few reproductive resources produced only female or male inflorescences, whereas individuals with many resources rarely had a high male ratio (i.e., number of male inflorescences/total number of inflorescences). Furthermore, the number of male inflorescences tended to reach an upper limit, whereas the number of female inflorescences increased monotonically with increasing reproductive investment. The patterns of floral sex allocation at the first- order branch level were analogous to those at the individual level. Thus, each first-order branch of B. platyphylla var. japonica behaves like an individual, and the floral sex allocation of a given branch does not necessarily represent the individual tree. The effect of the individual-level floral sex ratio on branch-level floral sex allocation indicates that branch behavior is controlled by the individual. Key words: first-order branch; floral sex allocation: individual; reproductive resources; wind-pollinated monoecy.

To increase our knowledge about mating-system evolution, we need to understand the relationship between specific floral traits and mating system. Species of Collinsia (Plantaginaceae) vary extensively in mating system; this variation is associated with variation in floral morphology and development and with the timing of self-pollination. Counterintuitively, large-flowered, more outcrossing species tend to have delayed stigma receptivity, reducing the amount of time that the stigma is receptive to cross-pollination before autonomous self-pollination. To understand how the timing of stigma receptivity is related to mating-system evolution, we studied in detail the timing of both stigma receptivity and self-pollination (anther-stigma contact) in two greenhouse-grown populations of large-flowered Collinsia heterophylla. Crosses on emasculated flowers at different stages of floral development always produced seeds, suggesting that cross-fertilization can be effected by pollen arriving prior to physiological receptivity. Phenotypic and genetic variation within populations in the timing of stigma receptivity and anther-stigma contact was substantial, although slightly less for the contact. Despite strong interspecific and interpopulation correlations, we did not find an among-genet phenotypic correlation between the traits. This indicates that each trait may respond independently to selection, and the trait association may be the result of correlational selection. Key words: Collinsia heterophylla; delayed selfing; delayed stigma receptivity; evolvability: flower development; beritability; mixed mating system; Plantaginaceae.

Plant fertility is a central subject of many questions in plant evolutionary and conservation biology. Pollen availability, abiotic resources, and flowering pattern can limit fruit and seed production. Open pollination and pollen supplementation studies are used to estimate any pollen limitation in natural populations. To study the impact of these factors on the reproductive success of Vriesea gigantea, an epiphytic bromeliad in the Atlantic Rainforest in Brazil, its fertility in four natural populations in Itapua State Park was assessed by considering plant and inflorescence size, flower production, fruit and seed set, flower and fruit set pattern, and seed viability and germination rate. Supplemental pollination in adult plants was used to determine whether fruit production in V. gigantea is limited by reception of pollen. The results showed that V. gigantea has a high production of flowers, fruits, and seeds. Seeds are highly viable in all populations, presenting an average germination rate of 94% (SE [+ or -] 3.5). Plants of V. gigantea from Itapua State Park are highly fertile. The high proportion of fruit and seed set after manual hand pollination indicates that the species is self-compatible. Pollination treatments showed evidence of pollinator limitation in the Itapua State Park population. Key words: Bromeliaceae; flower production; fruit set; Itapua State Park; pollen limitation; seed viability; self-compatibility.

Nectar production may disproportionately benefit male relative to female pollination success. In such cases, sexual selection is often suggested as the cause of asymmetric benefits, yet sexual selection in plants--particularly plants with hermaphroditic flowers--is infrequently tested empirically. Here, I used a protandrous herb with male-biased nectar production (Chrysothemis friedrichsthaliana, Gesneriaceae) to test predictions from sexual selection theory. During three flowering seasons, I measured nectar production, pollinator visits, and male and female fecundity following different numbers of cross-pollination events. In accordance with sexual selection predictions, (1) nectar production was greater during the male phase by at least 65%; (2) visits by the main pollinator (hummingbird Phaethornis striigularis) were limiting for part of the season, indicating that plants had to compete for pollinator visits; (3) pollinators spent 53% more time per visit and made 86% more visits to male- vs. female-phase flowers, suggesting that nectar increased male more than female pollination success; and (4) female fecundity was maximized by one visit, whereas male fecundity continued to increase with additional visits. Autonomous self-pollination further reduced visit requirements for maximum female seed set. These findings match specific sexual selection predictions: they link an observable male bias in a secondary sexual trait (nectar) to positive responses of mating participants (pollinators), resulting in more mating opportunities for mate-limited males, relative to apparently resource-limited females. This field-testing of theoretical predictions provides unique evidence that sexual selection helps maintain nectar production patterns in this and, quite likely, other hermaphroditic plant species. Key words: Chrysothemis friedrichsthaliana; Costa Rica; Gesneriaceae; hummingbird pollination; nectar; Phaethornis striigularis; pollinator-mediated selection; sexual selection.

Natural hybridization plays a critical role in speciation, the maintenance of reproductive isolation, and genetic introgression. While many plant species have hybrid swarms in areas of sympatry, the lack of hybrids among closely related sympatrically distributed species suggests that strong pre- and/or postzygotic barriers exist to hybridization. Gelsemium sempervirens and G. rankinii (Gelsemiaceae) are sympatrically distributed southeastern sister taxa that have strong postzygotic barriers to hybrid formation and high levels of genetic differentiation. In this study, two sympatric populations in Lowndes County, Georgia were surveyed from 1999-2005 to assess the role of temporal and pollinator isolation as potential prezygotic barriers. The populations had mostly non-overlapping flowering periods in 2003-2005, with significant differences in time of peak flowering and length of flowering. Both species shared a similar community of flower visitors, with the apid bee Habropoda laboriosa the dominant visitor to both species. A choice experiment found that H. laboriosa visited both species but preferred G. sempervirens. The primary prezygotic barrier is temporal isolation preventing hybridization in spite of the shared pollinators. This study suggests that reliance on a shared pollinator during speciation may limit opportunity for divergent selection on flowering time. Key words: floral isolation; Gelsemiaceae; Gelsemium; hybridization; prezygotic reproductive isolation; sympatry; temporal isolation.

When more pollen is present on stigmas than needed to fertilize all ovules, selection among pollen grains may occur due to effects of both pollen donors and maternal plants. We asked whether increasing plant age and flower age, two changes in maternal condition, altered the pattern of seed paternity after mixed pollination. We also asked whether changes in seed paternity affected offspring success in an experimental garden. While flower age did not affect seed paternity, there was a dramatic shift in pollen donor performance as plants aged. These differences were seen in the offspring as well, where the offspring of one pollen donor, which sired more seeds on young plants, flowered earlier in the season, and the offspring of another pollen donor, which sired more seeds on old plants, flowered later in tile season. Thus, change in maternal condition resulted in altered seed paternity, perhaps because the environment for pollen tube growth was different. The pattern of seed paternity and offspring performance suggests that pollen donors may show temporal specialization. Key words: Brassicaceae; flower age; mate choice; offspring fitness; plant age; pollen competition; sexual selection; wild radish.

Estimates of the sex ratio and cost of reproduction in plant populations have implications for resource use by animals, reserve design, and mechanisms of species coexistence, but may be biased unless all potentially reproductive individuals are censused over several flowering seasons. To investigate mechanisms maintaining dioecy in tropical forest trees, we recorded the flowering activity, sexual expression, and reproductive effort of all 2209 potentially reproductive individuals within 16 species of Myristicaceae over 4 years on a large forest plot in Amazonian Ecuador. Female trees invested > 10 times more biomass than males in total reproduction. Flowering sex ratios were male-biased in four species in [greater than or equal to] 1 year, and cumulative 4-year sex ratios were male-biased in two species and for the whole family, but different mechanisms were responsible for this in different species. Annual growth rates were equivalent for both sexes, implying that females can compensate for their greater reproductive investment. There was no strict spatial segregation of the sexes, but females were more often associated with specific habitats than males. We conclude that male-biased sex ratios are not manifested uniformly even after exhaustive sampling and that the mechanisms balancing the higher cost of female reproduction are extremely variable. Key words: dioecious; investment; Myristicaceae: reproduction; sex-ratio; tropical forest; Yasuni.

In distylous, self-incompatible plants, clonal propagation, unbalanced floral morpb frequencies, and reduced population size can interfere with the functioning of distyly by compromising legitimate intermorph pollinations, resulting in reduced reproductive output. Here, we examined the mating system and the impact of mate availability, population size, and spatial aggregation of morphs on reproductive output in the distylous, clonal, aquatic plant Hottonia palustris. Controlled pollinations under greenhouse conditions detected no spontaneous selfing without the action of a pollen vector (autonomous autogamy) and demonstrated very low fruit and seed development after self-pollination. Intermorph (legitimate) crossings resulted in high reproductive output in both floral morphs (long- and short-styled individuals), whereas intramorph (illegitimate) crossings decreased fruit and seed development by more than 50%, indicating that the species has partial intramorph-incompatibility. In natural populations, small population size and increasing deviation of floral morph frequencies negatively affected reproductive outcome. Individuals of the majority morph type developed significantly fewer fruit and seeds than individuals of the minority morph type. This rapid decline in fecundity was symmetrical, indicating that regardless of which morph was in the majority, the same patterns of negative frequency-dependent mating occurred. Increasing spatial isolation between compatible morphs significantly reduced fruit and seed set in both morphs similarly. This study provides clear indications of frequency- and context-dependent mating in natural populations of a distylous plant species. Key words: clonal propagation; frequency-dependent selection; heterostyly; Hottonia palustris; legitimate vs. illegitimate pollination; morph bias; pollen dispersal.

Many invasive species are benign in their native region--are there interactions between their key traits and the new habitats that explain invasion success? The giant perennial herb Heracleum mantegazzianum is a problematic invader in Europe and is also naturalized in North America. We compared its population structure and reproductive behavior in the native (W. Caucasus) and invaded (Czech Republic) areas in managed (pastures) and unmanaged sites. The age structure of the populations and age at flowering were analyzed using herb-chronology, a method based on counting annual rings in the secondary xylem of roots. The species was strictly monocarpic; most plants in unmanaged sites in the invaded range flowered in the third and fourth yr (maximum 12 yr). In unmanaged habitats, plants from the native range flowered later than those from the invaded range. In both ranges, flowering was delayed in managed sites where the population density was higher and most plants flowered around the fifth year. Reproductive output of individual plants was neither related to population density nor to age at flowering. More favorable climatic conditions in the invaded region, together with increased chances for dispersal in a densely colonized central Europe, seemed to allow the massive invasion. Key words: biogeography; Caucasus; Czech Republic; demography; habitat type; Heracleum mantegazzianum; herb-chronology; invasive alien plant.

Based on the general tendency tier females of dioecious plants to pay higher reproductive cost than males, it has been predicted that females should have much more reduced reproductive outputs and diminished vegetative production than males in energy-limited habitats. Nevertheless, this prediction has rarely been directly investigated. We investigated altitudinal changes in reproductive biomass and shoot production, normalized by plant size, for females and males of a shrub willow, Salix reinii, on Mr. Hakkoda, northeast Japan. Females maintained higher reproductive biomass than males at till altitudes; however, reproductive allocation for both sexes tended to decrease at a similar rate with an increase in altitude. Moreover, females vegetatively produced at the same rate as males at all altitudes. These findings suggest that females have a mechanism to compensate for the extra investment in reproduction irrespective of a changing environment. Shoot production did not change with altitude, suggesting that S. reinii gave priority to vegetative investment at the cost of reproductive output at higher altitudes. Inconsistent with general predictions, females did not respond more sensitively than males to severe environmental conditions in either reproductive allocation or shoot production, despite much higher resource investment in reproduction. Key words: altitudinal gradient; annual shoot production: dioecious shrub; Mr. Hakkoda, Japan; reproductive cost; reproductive effort; Salicaceae; Salix reinii.

Intersexua] differences in reproductive investments (RIs) (dry mass of reproductive tissue) at tree and branch levels in Eurya japonica were examined during two successive years. Mean total RIs per tree for males and females (adjusted for the mean trunk diameter in the combined sample trees. 25.7 mm) were 3.47 and 5.67 g dry mass. Females generally allocated about 1.6 times more biomass per tree to reproduction than males. On the other hand, male total RI per terminal branch averaged 51.6 mg dry mass and female averaged 226.6 mg. Females generally allocated about 4.4 times more biomass per terminal branch to reproduction than males. Thus, the magnitude of sexual difference at the tree level was much lower than that at the branch level. There were negative correlations between interyear fluctuation of total RI and stem diameter for both sexes. Interyear fluctuation of RI was greater for females than males in all size categories. This study revealed that conclusions from tree measures of RI differed from branch measures and suggested the importance of evaluating the average RI at the tree level for woody plants. I discussed the importance in adopting an effective sampling strategy for evaluating the RI at the tree level. Key words: dioecious plants; module levels; reproductive investment (RI); sex-related reproduction; size-related reproduction.

Inbreeding depression and selfing rate were investigated in the self-compatible vine Ipomoea hederacea to assess the variability of the breeding system. Inbreeding depression differed between populations and the magnitude varied at germination, growth (as measured by aboveground biomass), and reproductive potential. Plants from Macon County, Alabama, USA, had significant inbreeding depression (31%) at germination, but no significant inbreeding depression for aboveground biomass or number of reproductive structures (buds and flowers) at 45 d post germination in the greenhouse or in the field. Plants from Morgan County, Alabama, however, had significant inbreeding depression (>50%) for all three stages in the greenhouse. In allozyme comparisons, five of the II I. hederacea populations surveyed had high selfing rates (66.66-92.53%) and high levels of homozygosity ([F.sub.IS] = 0.500 0.861) in 2003, and three of four populations surveyed in 2004 had selfing rates that exceeded 50%. High selfing rates, high levels of homozygosity, and low levels of inbreeding depression suggest that inbreeding depression may not present a significant barrier to the transmission of selling alleles in some populations of I. hederacea, but does not account for the maintenance of a mixed mating system in other populations. Key words: allozyme; inbreeding depression; Ipomoea hederacea; mixed mating system; self-compatible.

Understanding the sources of variation in inbreeding depression within populations is important for understanding the evolution of selfing rates. At the population level, inbreeding depression is due to decreased heterozygosity caused by inbreeding, which decreases overdominance and increases the frequency of expression of recessive deleterious alleles. However, within individual families inbreeding has two distinct consequences: it reduces heterozygosity and it restricts the alleles present in offspring to those present in the parent. Outcrossing both increases heterozygosity and brings new alleles into a family (compared to the alleles present if the plant is self-pollinated). Both consequences of inbreeding affect offspring fitness, but the most common experimental design used to measure among-family variation in inbreeding depression cannot distinguish them. The result is that variance in inbreeding depression among families is confounded by genetic variation in the traits being measured. Also, correlations (among families) between measures of inbreeding depression or between inbreeding depression and mean trait values arc confounded by genetic variation in the traits being measured. I conclude that more complex crossing designs that allow estimation of breeding values for individual families are required to accurately detect and measure among-family variation in inbreeding depression. Key words: genetic variation; inbreeding depression; mating systems; outcrossing; selfing.

A new kind of stylar polymorphism, provisionally called inversostyly, is described. The polymorphism occurs in Hemimeris racemosa (Scrophulariaceae), a common annual herb of the Cape region of South Africa. Most populations arc dimorphic for style orientation: the style alterates with the two stamens and is deflected either upwards or downwards. Thus. there is reciprocal placement of the style and stamens in a vertical plane in zygomorphic flowers. The flowers arc symmetrical, and the floral parts do not vary in length. All flowers on a given plant are of the same stylar orientation. Pollination is by specialized oil-collecting bees (Rediviva spp.), which carry the pollen of the two morphs separately in discrete anterior or posterior locations on the underside of the body. Most inversostylous populations have a slightly higher proportion of the style-down morph, and this bias increases with decreasing pollinator abundance. In contrast with inversostylous populations, all individuals in homostylous populations of H. racemosa have the style and the stamens clustered together in the down position and high levels of autogamous seed set. Homostylous populations of H. racemosa, as well as the homostylous species Hemimeris sabulosa, occur where oil-collecting bees are less abundant. Key words: distyly; enantiostyly; evolution of selfing: Hemimeris sabulosa; heterostyly; mating system: morph ratio; reproductive biology.

Of the 340 genera in the Brassicaccae, apomictic reproduction is found only in the North American genus Boechera. We investigated phylogenetic relationships, ability to hybridize, mating system, and ploidy levels of 92 lines sampled from 85 populations and representing 19 Boechera species. Phylogenetic analyses based on chloroplast DNA sequences identified three lineages in the genus. Reciprocal crosses of each line were made to a common sexual diploid B. stricta tester. The resulting [F.sub.1] progeny were analyzed for the inheritance of polymorpbic microsatellite loci, genome size, and seed production. Intraspecific B. stricta crosses confirmed that this species is mostly diploid and sexual. Interspecific crosses revealed many other species were diploid and sexual and could be successfully hybridized with the tester. We also found obligate and facultative apomictic diploid and triploid lines. De novo [F.sub.1] polyploids (either triploids or tetraploids) were derived from the union of nonreduced (from an apomictic parent) and reduced (from the tester) gametes. However, seed production of these [F.sub.1] plants was generally low, suggesting a failure in the transmission of apomixis. The creation of a wide array of segregating genetic populations will facilitate future research on the evolution and inheritance of quantitative variation in Boechera. Key words: apomixis; Arabis; Boechera; Brassicaccae; genetic crossing; hybridization; microsatellites; polyploidy.

Most models of mating system evolution predict mixed mating to be unstable, although it is commonly reported from nature. Ecological interactions with mutualistic pollinators can help account for this discrepancy, but antagonists such as herbivores are also likely to play a role. In addition, inbreeding can alter ecological interactions and directly affect setting rates, which may also contribute to maintaining mating system variation. We explored herbivore and inbreeding effects on pollinator behavior and selfing rates in Mimulus guttatus. First, individual spittlebug (Philaenus spumarius) herbivores were applied to native plants in two populations. Spittlebugs reduced flower size, increased anther stigma distance, and increased selfing rates. A second experiment factorially crossed spittlebug treatment with inbreeding history (self- vs. cross-fertilized), using potted plants in arrays. Spittlebugs did not affect pollinator behavior, but they reduced flower size and nearly doubled the selfing rate. Inbreeding reduced the frequency of pollinator visits and increased flower-handling time, and this may be the first report that inbreeding affects pollinator behavior. Selfing rates of inbred plants were reduced by one half, which may reflect early inbreeding depression or altered pollinator behavior. The contrasting effects of herbivory and inbreeding on selfing rates may help maintain mating system variation in M. guttatus. Key words: California; herbivory: herkogamy; inbreeding; mating system; Mimulus guttatus; Phrymaceae; pollinator behavior.

Natural hybridization is increasingly recognized as an important process for the ecology and evolution of natural plant populations and species. There is a great need to initiate more studies based on natural populations in order to elucidate the possible role of hybrids in nature. The reproductive success of early generation hybrids can make or break hybrid lineages and may determine the genetic structure of hybrid swarms or the potential for gene flow through future generations, but studies of hybrid reproductive success arc lacking. Here we measured components of male and female reproductive success in Senecio jacobaea and S. aquaticus (Asteraceae) species and [F.sub.1] hybrids between these species trader laboratory conditions, and we measured reproductive output from crosses producing [F.sub.1] [F.sub.2], and backcross (BC) generation hybrids. [F.sub.1] hybrids were readily produced, and on average, the success of crosses producing subsequent generations ([F.sub.2], BC) decreased (though remained substantial), but the success of crosses was highly dependent on the genotypes involved. Also, [F.sub.1] hybrids were bigger, produced more flowers, and therefore produced more pollen than parental plants. Finally, crosses between parents were asymmetrical, such that S. aquaticus produced more and larger [F.sub.1] seeds than did S. jacobaea. Key words: Asteraceae; fertility; hybridization (hybridisation); male fitness; Netherlands; reproductive success; Senecio aquaticus; Senecio jacobaea.

We examined the frequency of hermaphroditic, monoccious, and dioecious species of angiosperms in restinga (sandy coastal plain) vegetation in SE Brazil. The study site was a vegetation mosaic comprising nine plant formations, ranging from open types to forest. Dioecy (14% of 566 species) was similar to other tropical vegetations and strongly associated with woodiness and entomophily. However, more interestingly, there was an exceptionally high percentage (35%) of dioecious species among the dominant woody plants. This pattern has not been previously reported, and we discuss the extent to which it is ecologically driven. We argue that the high abundance of dioecious plants in this resource-poor environment can be attributed to ecological traits related to long-distance dispersal, ecological vigor; and possibly, vegetative reproduction. Key words: dioecy: monocey: resource-poor environments; restingas; sandy coastal plains; sexual systems.

Gynodioecy is a dimorphic breeding system in which hermaphrodite and female individuals coexist in populations. Sex ratio and gender-relative lifetime seed production determine the stability of gynodioecy, and both genetic and ecological factors may influence these parameters. I analyzed the consequences of variation in population sex ratio and site elevation for the relative pollination success of female and hermaphrodite individuals of Daphne laureola in southern Spain, where previous studies failed to detect female fecundity advantages at two mid-elevation sites. Pollination success, estimated as stigmatic pollen loads, number of pollen tubes per style, and percentage of fertilized flowers, was higher for hermaphrodites than females in populations with 20-56% females. Furthermore, female quantitative disadvantage in pollination success increased with elevation, suggesting that the higher availability of pollen due to the increased proportion of hermaphrodites could not mitigate the negative effect that other factors associated with elevation apparently had on pollination. Supplemental hand pollinations showed that female seed production was pollen limited in populations with a proportion of females >50%, although both pollination success and natural fruit set of females in these sites were the highest recorded. Key words: altitudinal gradients; Daphne laureola; fruit set; gynodioecy: pollen competition: pollen limitation; pollen tube numbers; sex ratio.

Arisaema serratum possesses a pitfall-trap flower pollination system. However, little is known about the efficiency and pattern of pollen movement in A. serratum. Thus, the aims of this study are to (1) determine the paternal parents of the seeds and (2) elucidate pollen movement in a natural population. Paternity analysis using microsatellite markers was performed. Seeds were collected from a natural population of A. serratum in 2001 at Horigane, Japan. Small midges became trapped in female spathe tubes during the flowering period. We found that (1) seeds in a fruit were fertilized by multiple sires; (2) seeds sired by a paternal parent were either clumped, exclusively, or randomly distributed on the spadix, depending on the parent; (3) to a great extent, a few males contributed as sires; (4) distance from a female was not a factor in the inequality of reproductive success among males; (5) male reproductive success was not correlated with its size. We conclude that pollen carryover and the trap-flower pollination system are likely to result in multiple paternity and inequality in male success. Key words: Araceae; Arisaema; Japan; male success; microsatellite; paternity analysis; pollen carryover; trap flower.

Complementary field and laboratory tests confirmed and quantified the pollination abilities of Tranes sp. weevils and Cycadothrips chadwicki thrips, specialist insects of their respective cycad hosts, Macrozamia machinii and M. lucida. No agamospermous seeds were produced when both wind and insects were excluded from female cones; and the exclusion of wind-vectored pollen alone did not eliminate seed set, because insects were able to reach the cone. Based on enclosure pollination tests, each weevil pollinates an average 26.2 ovules per cone and each thrips 2.4 ovules per cone. These pollinators visited similar numbers of ovules per cone in fluorescent dye tests that traced insect movement through cones. Fluorescent dye granules deposited by Cycadothrips were concentrated around the micropyle of each visited ovule, the site of pollen droplet release, where pollen must be deposited to achieve pollination. In contrast, Tranes weevils left dye scattered on different areas of each visited ovule, indicating that chance plays a greater role in this system. Each weevil and 25 thrips delivered 6.2 and 5.2 pollen grains, respectively, on average, to each visited ovule per cone, based on examination of dissected pollen canals. In sum, the pollination potential of 25 Cycadothrips approximates that of one Tranes weevil. Key words: Macrozamia lucida; Macrozamia machinii; obligate pollination mutualisms; thrips; weevils; Zamiaceae.

Rainforests in tropical Australia occupy a very small, discontinuous area (< 1% of the continent), yet they are floristically diverse (c. 2800 vascular species) with high endemicity. There is a distinctive Gondwanan and autochthonous element, and some of the world's ancestral links to the basal angiosperms are uniquely found here. The rainforests can be evergreen or deciduous, but there is a distinct dry season with intermittent drought years. With these characters, the evolutionary pressures on species may be very different to that experienced elsewhere. Sexual systems of 1113 tree species (83 families) from northern Australia were compared with published accounts from the paleo- and neotropics. Hermaphroditic systems dominated all tree floras, and within all floras but Australia dioecy was the most common unisexual system. In tropical Australia, however, significantly more monoecy than dioecy occurred at landscape and community levels. Incorporating phylogeny revealed that sex and fruit types are significantly clustered. The Enphorbiaceae and Sapindaceae contributed c. 50% of the monoecious taxa. Inefficient pollinators (e.g., beetles) may have favored the maintenance of monoecy at the expense of dioecy in the Australian tropics although Key words: Australian rainforest; meta-analysis; monoecy; phylogenetic conservatism; pollinator efficiency; supertree.

Multiply sired fruits provide unambiguous evidence that pollen from two or more donors was deposited on a stigma and successfully fertilized ovules. Such multiple paternity within fruits can have important consequences for both parental and offspring fitness, but little is known about the frequency of multiple paternity or the mechanisms causing it. In this study we quantify the extent of multiple paternity in replicate experimental arrays of Mimulus ringens (square-stem monkeyflower) and use observations of pollinator behavior to infer mechanisms generating multiply sired fruits. In each array, floral displays were trimmed to two, four, eight, or 16 flowers per plant to span the range of display sizes observed in nature. In our sample of 204 fruits, more than 95% had two or more outcross pollen donors. The number of sires per fruit averaged 4.63 [+ or -] 0.10 (mean [+ or -] 1 SE), including selfs, and did not vary significantly with floral display treatment. Patterns of bumble bee foraging, combined with limited pollen carryover, suggest that observed levels of multiple paternity cannot be fully explained by single probes that deposited mixed pollen loads. Multiple probes to flowers, each delivering pollen from 1-3 different sires, are more likely to have caused the observed patterns. These sequential visits may reduce the potential for pollen competition and female choice based on pollen tube growth rate. Key words: Bombus; monkeyflower: multiple paternity; multiply sired fruits; paternity analysis; pollen carryover; pollination.

Ants are common flower visitors, but their effects on plant reproductive fitness have not often been assessed. Flower-visiting ants were studied to determine whether they are antagonists or mutualists and whether they could influence floral or breeding system evolution in gynodioecious wild strawberry (Fragaria virginiana). Ant and flying pollinator (bees/flies) access to plants was manipulated, and visitation, fruit, and seed set were assessed. Ants visited flowers of hermaphrodites more often than those of females when bees and flies were excluded, but visited the sex morphs equally when they were present. Insect class did not influence fruit or seed set of hermaphrodites. In contrast, ants had both positive and negative effects on seed set in females. Females visited only by ants had 90% of the seed set of those visited only by bees/flies, and their seed set increased with ant visitation. The spatial pattern of seed set, however, suggests that ants may also damage pistils. Lastly, in contrast to bees and flies, ants failed to increase visitation with floral display size, suggesting that ant presence at flowers could reduce selection on this attractive trait. Findings suggest that when in high abundance, flower-visiting ants could affect breeding system and floral evolution in this gynodioecious plant. Key words: ant plant interaction; ant pollination; floral evolution; Fragaria virginiana; gynodioecy; pollination; Rosaceae; sexual dimorphism.

Sexual dimorphism in plants has been known for over two millennia. However, little is known about how male and female reproduction of dioecious species will respond to anthropogenic environmental perturbations. Using growth chambers, the effects of C[O.sub.2] enrichment on male and female reproduction in Silene latifolia were examined and whether parental C[O.sub.2] environment affected progeny germination and sex ratio. Reproduction of male and female S. latifolia was enhanced by a similar magnitude at elevated C[O.sub.2]. Over the growing season, males produced 16 times as many flowers as females did fruits per plant, but no difference in reproductive biomass between genders was observed at ambient or elevated C[O.sub.2]. Germination of seeds produced by plants grown at different C[O.sub.2] concentrations was significantly different. Female seeds from higher C[O.sub.2]-grown plants tended to emerge earlier than those from ambientC[O.sub.2]-grown plants, but emergence of male seeds was little affected. Overall, seeds from elevated-C[O.sub.2]-grown plants had 20% higher germination and were more female-biased than those from ambient-C[O.sub.2]-grown plants. Because of the enhanced reproduction and more female-biased progeny under elevated C[O.sub.2], the population structure of this cosmopolitan weedy species will likely be altered in a future environment. Key words: Caryophyllaceae: dioecy; elevated C[O.sub.2]; global change: progeny performance; reproduction; Silene latifolia.

Hybridization between interfertile, sympatric or parapatric, plant species can be reduced significantly by conspecific pollen advantage (CPA), whereby conspecific pollen has an advantage over heterospecific pollen in terms of ovule fertilization. We examined CPA in two interfertile species of Senecio, S. aethnensis, and S. chrysanthemifolius (Asteraceae), which form a hybrid zone on Mt. Etna, Sicily. Individuals of both species were pollinated with pollen mixtures containing 0, 25, 50, 75, or 100% heterospecific pollen, and offspring were genotyped to determine if they were products of conspecific or heterospecific pollen fertilizing the ovules. The mean proportion of hybrid offspring produced on S. aethnensis plants was not significantly different to that expected based on the proportion of heterospecific pollen applied to the flower head. However, S. chrysanthemifolius mother plants showed moderate CPA, with the proportion of hybrid offspring significantly less than expected. Seed set or seed germination was not reduced, hence the CPA found for S. chrysanthemifolius acts before ovule fertilization. The consequences of asymmetry in CPA on the reproductive isolation of S. aethnensis are briefly discussed, along with other mechanisms that may play a role in the maintenance of the hybrid zone on Mt. Etna. Key words: Asteraceae; hybrid zone; introgression; Mt. Etna; pollen competition; reproductive isolation; Senecio.

Sawgrass, Cladium jamaicense, is the dominant macrophyte in the Florida Everglades. We examined sawgrass flowering phenology and compatibility reactions in ex situ and in situ populations over 2 yr. Sawgrass flowers in May in southern Florida. Flower maturation was relatively synchronous within an inflorescence. Along the entire inflorescence, functionally male flowers emerged initially, followed by stigmas, then anthers of hermaphroditic flowers. Flowers of each sex expanded over 2 d with less than 1 d in between, totaling 6-7 d for an inflorescence to complete flowering. Hand pollinations showed that sawgrass was self-compatible and not pollen-limited, because open pollinations produced fruit set similar to self- and cross- pollinations. Fruit set was low in autogamy and manipulation treatments. Manipulation treatments were used to study the effect of exposure to airborne pollen during hand pollinations. This treatment thus provides a useful technique for studies on the in situ compatibility of wind-pollinated graminoids. Sawgrass was able to self-fertilize, but the timing of flower maturation on an inflorescence promoted outcrossing. Actual outcrossing rates in sawgrass thus depend on clonal architecture and the timing of floral maturation on other inflorescences within a clone rather than on inflorescences of other genets in a population. Key words: anemophily; Cyperaceae; Everglades; protandry; protogyny; sawgrass; self-compatibility; wind pollination.