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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

How and why organisms are distributed as they are has long intrigued evolutionary biologists (1-4). The tendency for species to retain their ancestral ecology has been demonstrated in distributions on local and regional scales (5-7), but the extent of ecological conservatism over tens of millions of years and across continents has not been assessed (8-13). Here we show that biome stasis at speciation has outweighed biome shifts by a ratio of more than 25:1, by inferring ancestral biomes for an ecologically diverse sample of more than 11,000 plant species from around the Southern Hemisphere. Stasis was also prevalent in transocean colonizations. Availability of a suitable biome could have substantially influenced which lineages establish on more than one landmass, in addition to the influence of the rarity of the dispersal events themselves. Conversely, the taxonomic composition of biomes has probably been strongly influenced by the rarity of species' transitions between biomes. This study has implications for the future because if clades have inherently limited capacity to shift biomes (13), then their evolutionary potential could be strongly compromised by biome contraction as climate changes., In recent years, the extent to which species retain ancestral ecological traits and environmental distributions ('niche conservatism') has been debated (11,13-15). Whether ecology is evolutionarily labile or conserved appears to [...]

The evolutionary origins of the morphological and taxonomic diversity of angiosperms is poorly known. We used the genus Melianthus to explore the diversification of the southern African flora. Melianthus comprises eight species, and a phylogeny based on one nuclear and two plastid genes, as well as a morphological data set, confirmed that the genus is monophyletic. The two earliest diverging lineages are found in relatively mesic habitats, whereas the two terminal clades (an eastern and a western clade), each with three species, favor more arid habitats. The eastern clade is largely restricted to the summer-rainfall parts of southern Africa, and the western clade is found in winter-rainfall region. Molecular dating indicates a mid-Tertiary origin of the genus, with diversification of the eastern and western clades coincident with the Late Miocene--Pliocene uplift of the Escarpment mountains and the establishment of summer aridity along the west coast. The remarkably complex flowers are indicative of sunbird pollination, but many smaller birds can also visit. Speciation may be the consequence of allopatric divergence into edaphic--climatic niches. Divergence in flower and inflorescence morphology might be in response to the divergent pressures for nectar conservation in and regions coupled with the need for signaling to avian pollinators in generally shrubby vegetation. Key words: bird pollination; Cape flora; diversification; Melianthaceae; Melianthus; molecular dating; South Africa; speciation.

In most documented examples of adaptive radiation, the processes underlying divergence in form and function are poorly explored and remain speculative. Here, data from a comparative seedling growth experiment are used to explore growth form divergence in Ehrharta, a group of grasses that radiated in seasonally arid environments of the Cape region of South Africa. Seedlings of eight Ehrharta species of variable growth form were grown in liquid culture under conditions of high resource availabilty for 56 d, during which time changes in dry mass, allocation, and leaf parameters were measured. The results of this experiment reveal the existence of distinct seedling growth patterns that are associated with differences in adult plant form and seasonal drought survival strategy. Specifically, species that utilize a reseeding strategy have higher seedling growth rates and flower earlier than species that persist by vegetative means. A correlation between species' growth rates and their native substrates suggests that edaphic heterogeneity has been central in directing the evolution of alternative persistence strategies and growth forms. Parsimony reconstruction identifies slow growth and an association with nutrient-deficient sandstone-derived soils as ancestral in Ehrharta, with fast growth evolving after a transition to richer shale- and granite-derived soils. The emergence of annual species in two fast-growth lineages suggests that the latter is a key step in the evolution of an ephemeral strategy. An association between plant function and habitat identifies the radiation of Ehrharta as adaptive. Key words: adaptive radiation; allocation; annual; phylogeny; relative growth rate; specific leaf area.

Although Prionium is included in Juncaceae, rbcL sequence data indicate that Juncaceae is paraphyletic, with most genera closer to Cyperaceae than to Prionium. Cyperaceae and Juncales have embryological synapomorphies: thus embryology is used to test the monophyly of Juncaceae. The embryology of Prionium is described and its systematic position discussed. Material was prepared using standard methods of paraffin embedding. Additional embryological data were extracted from the literature. The anther in Prionium is tetrasporangiate, and the wall has an epidermis, an endothecium and middle layer, and an irregularly bilayered, glandular secretory tapetum. Microsporogenesis is probably simultaneous; pollen is ulcerate with a granular exine, in tetrahedral and cross tetrads, and trinucleate at release. The trilocular ovary contains many crassinucellate ovules probably having a Polygonum-type embryo sac. Endosperm is helobial and the embryo is of the Onagrad type, Juncus variation. The seed is testal-tegmic and germination is epigeal. The embryology of Prionium is most like that of Juncaceae, which shares several synapomorphies with Cyperaceae. Some of the characters in Cyperaceae may be interpreted as specialized forms of those found in Juncaceae. Embryology supports the monophyly of Cyperaceae and Juncales, but not Juncaceae; thus the position of Prionium remains unresolved. Key words: Cyperaceae; embryology; Eriocaulaceae; Flagellariaceae; Juncaceae; Prionium serratum; Typhaceae.

Author(s): James E. Richardson (corresponding author) [1, 2]; Frans M. Weitz [3, 4]; Michael F. Fay [1]; Quentin C. B. Cronk [5, 6]; H. Peter Linder [2, 4]; G. Reeves [...]

The evolution of reproductive isolation can be brought about either by divergent selection or through reinforcement and the potential role of shifts in pollination system in the speciation process was tested by using the Cape flora of South Africa as a model system. The results obtained were interpreted as evidence for reinforcement.

A study of the factors that have influenced evolution in Poales is presented. By the Paleogene the lineage has diversified into swamps, the forest understory, epiphytic habitats, and nutrient poor heathlands and the Neogene saw major diversifications of the grasses and possibly the sedges into fire-adapted vegetation in seasonal climates and low atmospheric CO(sub 2).

The prediction that, the evolution of the species richness in southern Africa and Southwestern Australia followed a similar temporal progression is tested. A comparison of the rates of lineage accumulation between the African and Australian Restionaceae is performed.

In this study, patterns of flowering phenology and species richness are compared, between abiotically and biotically pollinated plants, using phylogenetically independent contrasts. The results corroborate previous views that niche space is more constrained for abiotically pollinated species.

Research has been conducted on ehrharteoid grasses in the Cape region of South Africa. The hypothesis that high diversity of these grasses is the results of rapid radiation due to seasonally arid climate has been tested via the use of phylogenetic data, and the results are reported.

The systematic position of Montiniaceae remains uncertain: a relationship with Cornales has been suggested on phytochemical and embryological evidence, while molecular data point to a relationship with Solanales. We investigated the floral development and anatomy of the South African Montinia caryophyllacea to add a new set of characters for clarifying the systematic position of the family Montiniaceae. Pistillate inflorescences show a higher degree of reduction than staminate, with flowers set terminally on short lateral branches. Flowers have an irregular initiation sequence, with frequent abortions of organs. In Montinia, petals grow rapidly, and no zonal growth takes place. The gynoecium develops as a pit surrounded by a girdle. Placentation is basically parietal and becomes axillary by the postgenital fusion of placental lobes; unitegmic ovules are arranged in two parallel rows with adjacent ovules partly overlapping each other. Unisexuality is respectively attained at the stage of anther development and carpel initiation. The floral anatomy of pistillate and staminate flowers is illustrated and discussed. Observations on Montinia are compared with data of taxa from Saxifragaceae sensu stricto, Cornales, and Solanales. The absence of sympetaly in Montinia is discussed. Morphological and anatomical evidence points to a high similarity with Escalloniaceae. Although a position in the asterids is most probable, there is little support for the relationship with Solanales indicated by molecular data. Key words: Cornales; Escalloniaceae; floral anatomy; floral ontogeny; Montiniaceae; placentation; Saxifragaceae; Solanales; sympetaly.

The mature ovule and megagametophyte of 42 grass species (23 genera), mostly from the taxonomically troublesome subfamily Arundinoideae, was investigated. Haustorial synergids, first described from the Arundineae, are reported for a further 26 species (ten genera) of danthonioid grasses, a group for which they appear to be synapomorphic. The evolution of this character and a suite of associated integument and nucellar characters is discussed. The danthonioid clade, as defined by haustorial synergids, includes Cortaderia (often treated as nondanthonioid) but excludes a number of taxa currently contained in the Arundineae. The full extent of the group remains undetermined, however, since several of its potential members remain unstudied. The data provide some indication of phylogenetic structure within the elate. At least two of the species of Merxmuellera studied appear to occupy a basal position, while three do not, suggesting that this genus may be paraphyletic, or even polyphyletic. Also, the reduction or absence of synergid haustoria in Prionanthium, Pentaschistis, and Pentameris is considered to be secondarily derived and weakly corroborates the monophyly of this generic cluster as indicated by spikelet morphology.