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Summary While Sherwin J. Carlquist (1930–2021) did not originate the concept of long-distance dispersal and its role in evolution — a major pillar in Darwin’s theory (1859) — he almost single-handedly turned research on dispersal to insular habitats into an empirical and experimental research area. This contribution explains how and why this occurred based on Carlquist’s own papers and personal account, and provides a brief assessment of the historical context of his research on long-distance dispersal. I end on a personal note; in 1981, when I was a graduate student, Carlquist participated in a symposium on ‘Dispersal and Distribution’ in Hamburg, and the paper he gave there on intercontinental dispersal greatly influenced my own work.

A special‐purpose Committee on DNA Sequences as Types was established at the XIX International Botanical Congress (IBC) in Shenzhen, China, in 2017, with a mandate to report to the XX IBC in Madrid in 2024 with recommendations on a preferred course of action with respect to potential amendments of the International Code of Nomenclature for algae, fungi, and plants to allow DNA sequences as types. This is the first in an expected series of papers from the Special‐purpose Committee on this issue. We set out the background to the establishment of the Committee, explore key issues around typification that are pertinent to the question of DNA sequences as types, enumerate pros and cons of allowing DNA sequences as types, and foreshadow options for future discussion and potential recommendations.

PREMISE State‐sponsored weather stations became ubiquitous by the 1880s, yet many old climate data and phenological observations still need to be digitized and made accessible. METHODS We here make available flowering times for 450 species of herbs and shrubs gathered in 1844 by Carl Friedrich Philipp von Martius (1794–1868), director of the Munich Botanical Garden. The data formed part of the world’s third‐oldest phenological monitoring network as we explain in a brief overview of the history of such networks. Using data from one of the world’s oldest continuously functioning weather stations, Hohenpeißenberg, we relate temperature to flowering in three species with short flowering times and herbarium collections made since 1844 within the city’s perimeter, namely, Anemone patens, A. pulsatilla, and Arum maculatum. RESULTS Mean advances in flowering dates were 1.3–2.1 days/decade or 3.2–4.2 days/1°C warming. These advances are in keeping with similar advances in other European herbs during more recent periods. CONCLUSIONS Future studies might use the 1844 flowering data made available here as a source of information on the availability of particular flowers for specialized pollinators including insects looking for oviposition sites, such as the Psychoda flies that become trapped in Arum inflorescences. Another use of Martius’s 1844 data would be their incorporation into larger‐scale analyses of flowering in southern‐central Europe., American Journal of Botany, 108 (4), ISSN:1914-2016, ISSN:0002-9122

Hundreds of land plant lineages have independently evolved separate sexes in either gametophytes (dioicy) or sporophytes (dioecy), but 43% of all dioecious angiosperms are found in just 34 entirely dioecious clades, suggesting that their mode of sex determination evolved a long time ago. Here, we review recent insights on the molecular mechanisms that underlie the evolutionary change from individuals that each produce male and female gametes to individuals specializing in the production of just one type of gamete. The canonical model of sex chromosome evolution in plants predicts that two sex-determining genes will become linked in a sex-determining region (SDR), followed by expanding recombination suppression, chromosome differentiation and, ultimately, degeneration. Experimental work, however, is showing that single genes function as master regulators in model systems, such as the liverwort Marchantia and the angiosperms Diospyros and Populus. In Populus, this type of regulatory function has been demonstrated by genome editing. In other systems, including Actinidia, Asparagus and Vitis, two coinherited factors appear to independently regulate female and male function, yet sex chromosome differentiation has remained low. We discuss the best-understood systems and evolutionary pathways to dioecy, and present a meta-analysis of the sizes and ages of SDRs. We propose that limited sexual conflict explains why most SDRs are small and sex chromosomes remain homomorphic. It appears that models of increasing recombination suppression with age do not apply because selection favours mechanisms in which sex determination depends on minimal differences, keeping it surgically precise.

In 1917, sex chromosomes in plants were discovered in a liverwort with hetermorphic U and V chromosomes. Such heteromorphy is unexpected because, unlike the XY chromosomes in diploid-dominant plants, in haploid-dominant plants the female U and the male V chromosomes experience largely symmetrical potential recombination environments. Here we use molecular cytogenetics and super-resolution microscopy to study Frullania dilatata, a liverwort with one male and two female sex chromosomes. We applied a pipeline to Illumina sequences to detect abundant types of repetitive DNA and developed FISH probes to microscopically distinguish the sex chromosomes. We also determined the phenotypic population sex ratio because biased ratios have been reported from other liverworts with heteromorphic sex chromosomes. Populations had male-biased sex ratios. The sex chromosomes are monocentric, and of 14 probes studied (eight satellites, five transposable elements and one plastid region), four resulted in unique signals that differentiated the sex chromosomes from the autosomes and from each other. One FISH probe selectively marked the centromeres of both U chromosomes, so we could prove that during meiosis each U chromosome associates with one of the opposite telomeres of the V chromosome, resulting in a head-to-head trivalent. The similarity of the two U chromosomes to each other in size and in their centromere FISH signal positions points to their origin via a non-disjunction event (aneuploidy), which would fit with the general picture of sex chromosomes rarely crossing-over and being prone to suffer from non-disjunction.

Background and Aims Unlike other nuclear genes in eukaryotes, rDNA genes (5S and 35S loci) are present in numerous copies per cell and, when stained, can therefore provide basic information about genome organization. In tracheophytes (vascular plants), they are usually located on separate chromosomes, the so-called S-type organization. An analysis of 1791 species of land plants suggested that S-type arrays might be ancestral in land plants, while linked (L-type) organization may be derived. However, no outgroup and only a handful of ferns and bryophytes were included. Methods We analysed genome sizes and the distribution of telomere, 5S and 35S rDNA FISH signals in up to 12 monoicous or dioicous species of liverworts from throughout a phylogeny that includes 287 of the 386 currently recognized genera. We also used the phylogeny to plot chromosome numbers and the occurrence of visibly distinct sex chromosomes. Key Results Chromosome numbers are newly reported for the monoicous Lejeunea cavifolia and for females of the dioicous Scapania aequiloba. We detected sex-related differences in the number of rDNA signals in the dioicous Plagiochila asplenioides and Frullania dilatata. In the latter, the presence of two UU chromosomes in females and additional 5S-35S rDNA loci result in a haploid genome 0.2082 pg larger than the male genome; sex-specific genome differences in the other dioicous species were small. Four species have S-type rDNA, while five species have mixed L-S rDNA organization, and transitions may have occurred multiple times, as suggested by rDNA loci not being conserved among closely related species of Pellia. All species shared an Arabidopsis-like telomere motif, and its detection allowed verification of the chromosome number of Radula complanata and chromosome rearrangements in Aneura pinguis and P. asplenioides, the latter also showing sex-specific interstitial telomere repeats. Conclusions The S and L rDNA arrangements appear to have evolved repeatedly within liverworts, even in the same species. Evidence for differential accumulation of rDNA between the sexes so far is limited.

Coriariaceae comprise only Coriaria , a genus of shrubs with nine species in Australasia (but excluding Australia), five in the Himalayas, Taiwan, the Philippines, and Japan, one in the Mediterranean, and one ranging from Patagonia to Mexico. The sister family, Corynocarpaceae, comprises five species of evergreen trees from New Guinea to New Zealand and Australia. This distribution has long fascinated biogeographers as potential support for Wegener's theory of continental drift, with alternative scenarios invoking either Antarctic or Beringian range expansions. Here, we present the discovery of pollen grains from Early Campanian (ca. 82 Mya) deposits in Antarctica, which we describe as Coriaripites goodii sp. nov., and newly generated nuclear and plastid molecular data for most of the family's species and its outgroup. This greatly expands the family's fossil record and is the so far oldest fossil of the order Cucurbitales. We used the phylogeny, new fossil, and an Oligocene flowering branch assigned to a small subclade of Coriaria to generate a chronogram and to study changes in chromosome number, deciduousness, and andromonoecy. Coriaria comprises a Northern (NH) and a Southern Hemisphere (SH) clade that diverged from each other in the Paleocene (ca. 57 Mya), with the SH clade reaching the New World once, through Antarctica, as supported by the fossil pollen. While the SH clade retained perfect flowers and evergreen leaves, the NH clade evolved andromonoecy and deciduousness. Polyploidy occurs in both clades and points to hybridization, matching weak species boundaries throughout the genus.

Squamellaria is a genus of epiphytic Rubiaceae which has been domesticated by ants on the Fiji islands. One species is on the verge of extinction.

Watermelons are among the most important vegetable crops worldwide, but targeted breeding is hindered by problems with Citrullus taxonomy. Here we clarify nomenclature and species relationships in Citrullus, its chromosome numbers, and the likely geographic region of watermelon domestication. We correct an erroneous chromosome count in recent literature, provide a count for an understudied species, and data on chromosome numbers for the entire genus. We also use a nuclear/plastid locus phylogeny to summarize data on Citrullus sexual systems, loss of tendrils, life history, and geographic ranges. Key insights from new sequences are that (i) material of C. vulgaris var. "colocynthoides", collected by Schweinfurth in Egypt in 1882 represents the colocynth, C. colocynthis, and (ii) the citron or bitter watermelon, C. amarus, is indeed a separate species, not a subspecies of the dessert watermelon. Schweinfurth's varietal name, a nomen nudum, has been widely used for seeds as old as 5400 BP, and it now needs to be investigated whether these seeds are colocynths, watermelon or a hybrid. To help improve Citrullus taxonomy and nomenclature, we allocate some 50 scientific names to seven biological species, tabulate chromosome counts, and provide notes on misidentified germplasms traceable by accession numbers. More wild-collected herbarium-verified material from northeast Africa is urgently needed, especially given the discovery of Russian breeders that populations of wild "cordophanus" from Sudan are closer to the cultivated watermelon than are any other wild populations so far known.

Herbarium specimens deposited in publicly accessible collections are the basis for all scientific names because only permanent specimens can be re-studied by independent researchers, the very essence of science. Re-investigations may be done with morphological, chemical, genomic, computer-tomographic, or other methods. Based on new herbarium material, I here provide a name for the Xishuangbanna gourd, a plant long cultivated in Yunnan because of its large non-bitter fruits, rich in β-carotene. Genome re-sequencing of numerous accessions has shown that this cucumber mutant is closer to Cucumis sativus var. sativus than is the wild bitter-fruited progenitor C. sativus var. hardwickii, and two dozen studies have further clarified the genetics of key traits, including pulp color, fruit shape, and flowering times. Morphological and molecular diagnoses of the new variety are provided and museum-quality specimens have been distributed to the World’s major herbaria.

The three bryophyte lineages have longy-lived gametophytes that are either bisexual, producing both male- and female gametes, or sexually specialized and then producing only one type of gamete. Phylogenies suggest repeated evolutionary switches between these systems, implying that bryophyte sex chromosomes may have been gained and lost repeatedly. How this occurred is poorly understood, even though plant sex chromosomes were first discovered in liverworts. We explain how the sex chromosomes of haploid-dominant organisms are distinct from the better-studied X-Y and Z-W systems in the tree of life, summarise what is known about their distribution and genetic composition, and present new cytogenetic data for Frullania dilatata and Plagiochila asplenioides, the former with two U chromosomes and one V chromosome, the latter with one U chromosome and two V chromosomes; male and female C-values in F. dilatata are correspondingly asymmetric (the C-value of P. asplenioides is only known for female nuclei). So far, there is a lack of high-throughput sequencing, quantification, and in situ study of the repetitive DNA, organellar DNA, and transposable elements, and it is therefore not known what causes the size difference of U and V chromosomes from the autosomes or each other. Heterochromatin was also first discovered in bryophytes, but its function in their sex regulation has not been addressed. Studies of bryophyte sex chromosomes with combined cytogenetic and genomic approaches are fundamental for fuller understanding of s sex chromosome evolution across the tree of life.

Premise The proportion of woody dicots with toothed leaves increases toward colder regions, a relationship used to reconstruct past mean annual temperatures. Recent hypotheses explaining this relationship are that (1) leaves in colder regions are thinner, requiring thick veins for support and water supply, with the resulting craspedodromous venation leading to marginal teeth (support–supply hypothesis) or that (2) teeth are associated with the packing of leaf primordia in winter buds (bud‐packing hypothesis). Methods We addressed these hypotheses by examining leaf thickness, number of primordia in buds, growing season length (mean annual temperature, MAT), and other traits in 151 deciduous woody species using georeferenced occurrences and a Bayesian model controlling for phylogeny. We excluded evergreen species because longer leaf life spans correlate with higher leaf mass per area, precluding the detection of independent effects of leaf thickness on leaf‐margin type. Results The best model predicted toothed leaves with 94% accuracy, with growing season length the strongest predictor. Neither leaf thickness nor number of leaves preformed in buds significantly influenced margin type, rejecting the support–supply and bud‐packing hypotheses. Conclusions A direct selective benefit of leaf teeth via a carbon gain early in the spring as proposed by Royer and Wilf (2006) would match the strong correlation between toothed species occurrence and short growing season found here using Bayesian hierarchical models. Efforts should be directed to physiological work quantifying seasonal photosynthate production in toothed and nontoothed leaves., American Journal of Botany, 106 (11), ISSN:1914-2016, ISSN:0002-9122

Lobelioideae comprise about 1200 species in 30 genera worldwide and include famous cases of parallel evolution in the "giant rosette" lobelias occurring in East Africa, Hawaii, and Bhutan. To date, no phylogeny has included the Himalayan giant lobelia, and its age and phylogenetic distance from the Hawaiian and African giant species (the latter in the same section as the Bhutan species) are therefore unknown. Asian Lobelioideae in general have received little attention, partly because of the difficult access to material. Here we use nuclear and plastid markers of Lobelioideae (with worldwide sampling) to test the monophyly of the section that includes most Asian lobelias, and we then use a reduced concatenated matrix to resolve the position of Lobelia nubigena from Bhutan and of the likewise cold-adapted lowland species L. sessilifolia. Most sequences come from herbarium material. Lobelia nubigena diverged from its Asian lowland relatives 13.8 (12.6-15) million years ago (about the time of the Bhutan Himalaya orogeny), and in an unexpected twist, L. sessilifolia is the sister species to a huge Glade (ca. 265 species) that comprises African, South American, Asian, and the entire Hawaiian Lobelioideae radiation. The African and Hawaiian high-elevation lobelias in our sample are younger than L. nubigena, although the time when gigantism evolved in this species cannot be precisely inferred. Our results support the previously hypothesized Asian origin of (1) the Hawaiian Lobelioideae, (2) Southeast Asian islands lobelias, and (3) the African Lobelia-Rynchopetalum group, which also reached South America.

Some of the World's most valuable crops, including watermelon, honey melon, cucumber, squash, zucchini and pumpkin, belong to the family Cucurbitaceae. We review insights on their domestication from new phylogenies, archaeology and genomic studies. Ancestral state estimation on the most complete Cucurbitaceae phylogeny to date suggests that an annual life cycle may have contributed to domestication. Domestication started c. 11 000 years ago in the New World and Asia, and apparently more recently in Africa. Some cucurbit crops were domesticated only once, others multiple times (e.g. melon from different Asian and African populations). Most wild cucurbit fruits are bitter and nonpalatable to humans, and nonbitterness of the pulp apparently was a trait favoured early during domestication, with genomic data showing how bitterness loss was achieved convergently. The genetic pathways underlying lycopene accumulation, red or orange pulp colour, and fruit size and shape are only just beginning to be understood. The study of cucurbit domestication in recent years has benefitted from the increasing integration of archaeological and genomic data with insights from herbarium collections, the most efficient way to understand species' natural geographic ranges and climate adaptations.

True agriculture - defined by habitual planting, cultivation, harvesting and dependence of a farmer on a crop - is known from fungi farmed by ants, termites or beetles, and plants farmed by humans or ants. Because farmers supply their crops with nutrients, they have the potential to modify crop nutrition over evolutionary time. Here we test this hypothesis in ant/plant farming symbioses. We used field experiments, phylogenetic-comparative analyses and computed-tomography scanning to investigate how the evolution of farming by ants has impacted the nutrition of locally coexisting species in the epiphytic genus Squamellaria (Rubiaceae). Using isotope-labelled mineral and organic nitrogen, we show that specialised ants actively and exclusively fertilise hyperabsorptive warts on the inner walls of plant-formed structures (domatia) where they nest, sharply contrasting with nitrogen provisioning by ants in nonfarming generalist symbioses. Similar hyperabsorptive warts have evolved repeatedly in lineages colonised by farming ants. Our study supports the idea that millions of years of ant agriculture have remodelled plant physiology, shifting from ant-derived nutrients as by-products to active and targeted fertilisation on hyperabsorptive sites. The increased efficiency of ant-derived nutrient provisioning appears to stem from a combination of farming ant behaviour and plant 'crop' traits.

PREMISE Parasitic plants with large geographic ranges, and different hosts in parts of their range, may acquire horizontally transferred genes (HGTs), which might sometimes leave a footprint of gradual host and range expansion. Cynomorium coccineum, the only member of the Saxifragales family Cynomoriaceae, is a root holoparasite that occurs in water-stressed habitats from western China to the Canary Islands. It parasitizes at least 10 angiosperm families from different orders, some of them only in parts of its range. This parasite therefore offers an opportunity to trace HGTs as long as parasite-host pairs can be obtained and sequenced. METHODS By sequencing mitochondrial, plastid, and nuclear loci from parasite-host pairs from throughout the parasite's range and with prior information from completely assembled mitochondrial and plastid genomes, we detected 10 HGTs of five mitochondrial genes. RESULTS The 10 HGTs appear to have occurred sequentially as C. coccineum expanded from East to West. Molecular-clock models yield Cynomorium stem ages between 66 and 156 Myr, with relaxed clocks converging on 66-67 Myr. Chinese Sapindales, probably Nitraria, were the first source of transferred genes, followed by Iranian and Mediterranean Caryophyllales. The most recently acquired gene appears to come from a Tamarix host in the Iberian Peninsula. CONCLUSIONS Data on HGTs that have accumulated over the past 15 years, along with this discovery of multiple HGTs within a single widespread species, underline the need for more whole-genome data from parasite-host pairs to investigate whether and how transferred copies coexist with, or replace, native functional genes.

Climate warming is leading to earlier budburst and therefore an increased risk of spring frost injury to young leaves. But to what extent are second-cohort leaves, which trees put out after leaf-killing frosts, able to compensate incurred losses? To investigate whether second-cohort leaves behave differently from first-cohort leaves, we exposed saplings of beech (Fagus sylvatica), oak (Quercus robur), and honeysuckle (Lonicera xylosteum) to experimental treatments mimicking either a warm spring or a warm spring with a leaf-killing frost. Refoliation took 48, 43, and 36 d for beech, oak and honeysuckle, respectively. In beech and oak, autumn Chl content and photosynthesis rates were higher in second- than in first-cohort leaves, senescence in second-cohort leaves occurred c. 2-wk-later, and autumn bud growth in beech was elevated 66% in frost-damaged plants compared with the warm spring treatment. No differences in autumn phenology and growth were observed for honeysuckle. Overall, in beech and oak, delayed Chl breakdown in second-cohort leaves mitigated 31% and 25%, respectively, of the deficit in growing-season length incurred by spring frost damage. These results reveal an unexpected ability of second-cohort leaves of beech and oak to compensate for spring frost damage, and demonstrate that long-lived trees vary their autumnal phenology depending on preceding productivity.

Introduction Gnetophytes, comprising the genera Ephedra, Gnetum and Welwitschia, are an understudied, enigmatic lineage of gymnosperms with a controversial phylogenetic relationship to other seed plants. Here we examined the organization of ribosomal DNA (rDNA) across representative species. Methods We applied high-throughput sequencing approaches to isolate and reconstruct rDNA units and to determine their intragenomic homogeneity. In addition, fluorescent in situ hybridization and Southern blot hybridization techniques were used to reveal the chromosome and genomic organization of rDNA. Key results The 5S and 35S rRNA genes were separate (S-type) in Gnetum montanum, Gnetum gnemon and Welwitschia mirabilis and linked (L-type) in Ephedra altissima. There was considerable variability in 5S rDNA abundance, ranging from as few as ~4000 (W. mirabilis) to >100 000 (G. montanum) copies. A similar large variation was also observed in 5S rDNA locus numbers (two to 16 sites per diploid cell). 5S rRNA pseudogenes were interspersed between functional genes forming a single unit in E. altissima and G. montanum. Their copy number was comparable or even higher than that of functional 5S rRNA genes. In E. altissima internal transcribed spacers of 35S rDNA were long and intrinsically repetitive while in G. montanum and W. mirabilis they were short without the subrepeats. Conclusions Gnetophytes are distinct from other gymnosperms and angiosperms as they display surprisingly large variability in rDNA organization and rDNA copy and locus numbers between genera, with no relationship between copy numbers and genome sizes apparent. Concerted evolution of 5S rDNA units seems to have led to the amplification of 5S pseudogenes in both G. montanum and E. altissima. Evolutionary patterns of rDNA show both gymnosperm and angiosperm features underlining the diversity of the group.

We analysed plant collecting in Germany between 1826 and 2014 by counting specimens of common, rare, and invasive species deposited in the herbaria of Munich during that period. Plant collecting increased in the late 1940s and continued until the mid-1980s, but has since declined to levels similar to 1900. In spite of the decline in collecting, the number of specimens of invasive species has strongly increased. The only other attempt to analyse botanical collecting in a large European region, an analysis of botanical recording in the British Isles 1836 to 1988, did not find a decline by the mid-1980s. For the United States, an analysis of collecting between the 1890s and 1999 found that it peaked in the 1930s. Museum time-series (representing the same species collected at different times) have been integral to identifying temporal responses to environmental change, for example, changed flowering times in response to an earlier onset of spring and the change of a region's floristic composition. A possible way to combat the likely loss of time-series in European herbaria is for collection personal to engage with biology teachers at high schools and universities to encourage the collecting of local plants as part of courses in the life sciences.

Ephedra, Gnetum, and Welwitschia constitute the gymnosperm order Gnetales of still unclear phylogenetic relationships within seed plants. Here we review progress over the past 10 years in our understanding of their species diversity, morphology, reproductive biology, chromosome numbers, and genome sizes, highlighting the unevenness in the sampling of species even for traits that can be studied in preserved material, such as pollen morphology. We include distribution maps and original illustrations of key features, and specify which species groups or geographic areas are undersampled.

Dactylorhiza sambucina (L.) Soo is a polycarpic perennial herb occurring in the Central European, Eastern European, and Balkan floristic provinces. At the European scale, the IUCN considers it a species of “least concern”. This paper reviews the taxonomic status, morphology, distribution, habitat requirements, mycorrhizal associations, and life cycle of D. sambucina , with special emphasis on its reproduction. We also summarize information on chromosome numbers and genetic variation. Our data from 12 years of monitoring D. sambucina in the Czech Republic show that three to four leaves have to be produced prior to flowering; plants with five and more leaves flower regularly. Juvenile plants near adult plants suggest recruitment from seeds. About 20% of our 450 monitored plants underwent dormancy (failure of mature plants to produce above-ground parts in one or more growing seasons), the maximum duration being eight years. After reappearance, these individuals were usually sterile for the next year. Mortality was highest (24%) at the seedling stage. Regarding the purple/yellow flower colour polymorphism that characterizes D. sambucina , we found no correlation between morph frequency and soil properties (pH, calcium content), population density, or altitude above sea level.

Summary Experimental data on the perception of day length and temperature in dormant temperate zone trees are surprisingly scarce. In order to investigate when and where these environmental signals are perceived, we carried out bagging experiments in which buds on branches of Fagus sylvatica, Aesculus hippocastanum and Picea abies trees were exposed to natural light increase or kept at constant 8-h days from December until June. Parallel experiments used twigs cut from the same trees, harvesting treated and control twigs seven times and then exposing them to 8- or 16-h days in a glasshouse. Under 8-h days, budburst in Fagus outdoors was delayed by 41 d and in Aesculus by 4 d; in Picea, day length had no effect. Buds on nearby branches reacted autonomously, and leaf primordia only reacted to light cues in late dormancy after accumulating warm days. Experiments applying different wavelength spectra and high-resolution spectrometry to buds indicate a phytochrome-mediated photoperiod control. By demonstrating local photoperiodic control of buds, revealing the time when these signals are perceived, and showing the interplay between photoperiod and chilling, this study contributes to improved modelling of the impact of climate warming on photosensitive species.

Differing from most animals, plants have an indeterminate body plan, allowing them to add new body parts throughout their lifetime. The realized modular construction of a plant is the result of endogenous processes and exogenous constraints. Plant architectural analysis provides a holistic approach to whole-plant development by disentangling endogenous processes from exogenous constraints. Such analyses have focused more on trees than herbs. We here report a rare growth form discovered in the tropical herb Centella asiatica (Apiaceae) using micro-computed X-ray tomography to understand organogenesis in the meristem. Seeds of C. asiatica germinate to give rise to an orthotropic monochasium (sympodium) with terminal inflorescences. A stolon subsequently emerges from the oldest leaf axils of the sympodium. The primary growth of stolons is indeterminate (monopodial), and they only bear scale leaves. The stolon not only produces new leafy sympodial shoots at each node but also an axillary inflorescence. To place this growth form in context, we illustrate all architectural models so far reported from herbs. Our study highlights the complexity of herb architectures and illustrates the use of a novel methodology to decipher plant branching modes.

SummaryType specimens are permanently preserved biological specimens that fix the usage of species names. This method became widespread from 1935 onwards and is now obligatory. We used DNA sequencing of types and more recent collections of wild and cultivated melons to reconstruct the evolutionary history of the genus Citrullus and the correct names for its species. We discovered that the type specimen of the name Citrullus lanatus, prepared by a Linnaean collector in South Africa in 1773, is not the species now thought of as watermelon. Instead, it is a representative of another species that is sister to C. ecirrhosus, a tendril-less South African endemic. The closest relative of the watermelon instead is a West African species. Our nuclear and plastid data furthermore reveal that there are seven species of Citrullus, not four as assumed. Our study implies that sweet watermelon originates from West, not southern Africa as previously believed, and that the South African citron melon has been independently domesticated. These findings affect and explain numerous studies on the origin of these two crops that led to contradictory results because of the erroneous merging of several distinct species.

SummaryAnt-plant symbioses involve over 110 ant species in five subfamilies that are facultative or obligate occupants of stem, leaf or root domatia formed by hundreds of ant-plant species. The phylogenetic distribution and geological ages of these associations, and the frequency of gains or losses of domatium, are largely unknown. We compiled an up-to-date list of ant domatium-bearing plants, estimated their probable true number from model-based statistical inference, generated dated phylogenies that include c. 50% of ant-plant lineages, and traced the occurrence of domatia and extrafloral nectaries on a 1181-species tree, using likelihood and Bayesian methods. We found 681 vascular plants with domatia (159 genera in 50 families) resulting from minimally 158 inferred domatium origins and 43 secondary losses over the last 19 Myr. The oldest African ant-plant symbioses are younger than those in Australasia and the Neotropics. The best statistical model suggests that the true number of myrmecophytes may approach 1140 species. The phylogenetic distribution of ant-plants shows that domatia evolved from a range of pre-adapted morphological structures and have been lost frequently, suggesting that domatia have no generalizable effect on diversification. The Miocene origin of ant-plant symbioses is consistent with inferred changes in diet and behaviour during ant evolution.

Many epiphytic plants have associated with ants to gain nutrients. Here, we report a novel type of ant–plant symbiosis in Fiji where one ant species actively and exclusively plants the seeds and fertilizes the seedlings of six species of Squamellaria (Rubiaceae). Comparison with related facultative ant plants suggests that such farming plays a key role in mutualism stability by mitigating the critical re-establishment step. Mutualisms are common in nature. In Fiji, a species of ant selects, disperses and fertilizes an epiphytic plant in an exclusive symbiosis. This represents a novel example of plant farming by ants.

Background and Aims Resin is a defence against herbivores and a floral reward in a few African and South American species whose bee pollinators collect it for nest construction. Here we describe a new role for floral resin from the Asian genus Kadsura (Schisandraceae). Kadsura tepals tightly cover a globe formed by carpels (in females) or near-fused stamens with fleshy connectives (in male flowers of most, but not all species). Methods We carried out field observations at four sites in China and used pollinator behavioural assays, chemical analyses and time-calibrated insect and plant phylogenies to investigate the specificity of the interactions and their relationship to floral structure. Key Results Nocturnal resin midges (Resseliella, Cecidomyiidae) walk around on the flowers’ sexual organs to oviposit, thereby transferring pollen and wounding tissues. The larvae then develop in resin-filled chambers. Male and female floral scents are dominated by α-pinene, while the resinous exudate is dominated by caryophyllene. As revealed by barcoding of multiple midge larvae per flower species, the mutualisms are species specific and appear to have evolved over the past 6–9 million years. Conclusions Resin feeding, not pollen or ovule feeding, by midge larvae explains the abundant Kadsura exudates, highlighting the poorly known world of nocturnal flower–fly interactions.

Combining molecular cytogenetics and phylogenetic modelling of chromosome number change can shed light on the types of evolutionary changes that may explain the haploid numbers observed today. Applied to the monocot family Araceae, with chromosome numbers of 2n = 8 to 2n = 160, this type of approach has suggested that descending dysploidy has played a larger role than polyploidy in the evolution of the current chromosome numbers. To test this, we carried out molecular cytogenetic analyses in 14 species from 11 genera, using probes for telomere repeats, 5S rDNA and 45S rDNA and a plastid phylogenetic tree covering the 118 genera of the family, many with multiple species. We obtained new chromosome counts for six species, modelled chromosome number evolution using all available counts for the family and carried out fluorescence in situ hybridization with three probes (5S rDNA, 45S rDNA and Arabidopsis-like telomeres) on 14 species with 2n = 14 to 2n = 60. The ancestral state reconstruction provides support for a large role of descending dysploidy in Araceae, and interstitial telomere repeats (ITRs) were detected in Anthurium leuconerum, A. wendlingeri and Spathyphyllum tenerum, all with 2n = 30. The number of ITR signals in Anthurium (up to 12) is the highest so far reported in angiosperms, and the large repeats located in the pericentromeric regions of A. wendlingeri are of a type previously reported only from the gymnosperms Cycas and Pinus. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177, 15–26.

Summary � Leaf out phenology affects a wide variety of ecosystem processes and ecological interactions and will take on added significance as leaf out times increasingly shift in response to warming temperatures associated with climate change. There is, however, relatively little information available on the factors affecting species differences in leaf out phenology. � An international team of researchers from eight Northern Hemisphere temperate botanical gardens recorded leaf out dates of c. 1600 woody species in 2011 and 2012. � Leaf out dates in woody species differed by as much as 3 months at a single site and exhibited strong phylogenetic and anatomical relationships. On average, angiosperms leafed out earlier than gymnosperms, deciduous species earlier than evergreen species, shrubs earlier than trees, diffuse and semi-ring porous species earlier than ring porous species, and species with smaller diameter xylem vessels earlier than species with larger diameter vessels. The order of species leaf out was generally consistent between years and among sites. � As species distribution and abundance shift due to climate change, interspecific differences in leaf out phenology may affect ecosystem processes such as carbon, water, and nutrient cycling. Our open access leaf out data provide a critical framework for monitoring and modelling such changes going forward.

The lily family Colchicaceae consists of geophytic herbs distributed on all continents except the Neotropics. It is particularly diverse in southern Africa, where 80 of the 270 species occur. Colchicaceae exhibit a wide range of ploidy levels, from 2n = 14 to 2n = 216. To understand where and how this cytogenetic diversity arose, we generated multilocus phylogenies of the Colchicaceae and the Colchicum clade that respectively included 85 or 137 species plus relevant outgroups. To infer the kinds of events that could explain the observed numbers in the living species (dysploidy, polyploidization, or demi-duplication, i.e. fusion of gametes of different ploidy), we compared a series of likelihood models on phylograms, penalized likelihood ultrametric trees, and relaxed clock chronograms that contained the 58 or 112 species with published chromosome counts. While such models involve simplification and cannot address the processes behind chromosomal rearrangements, they can help frame questions about...

The circumscription of the five to eight species of Luffa, as well as their correct names, have long been problematic. Experts on the genus, most recently C. Heiser and C. Jeffrey, have disagreed on the number of species in the New World and the application of the name L. operculata, which in turn affected the names L. quinquefida and L. sepium. Heiser used classic biosystematic methods, including experimental crossing, to infer species boundaries, but neither researcher had today's option of using DNA sequences for this purpose. We sequenced 51 accessions of Luffa, representing the geographic range of the genus and as much as possible topotypical or type material. Phylogenies from four non-coding plastid regions and the nuclear ribosomal DNA spacer region show that eight clades of specimens have geographic-morphological coherence. Heiser's view that Luffa has three species in the New World is supported, and there are four species in tropical and subtropical Asia. Australia has an endemic species...

• Premise of the study: The Foulden Maar lake sediments in Otago, South Island, New Zealand, date to the earliest Miocene and provide an important picture of the diversity of the Australasian biota, paleoecology, and climate at a time when New Zealand had a smaller land area than today. The diverse rainforest contains many taxa now restricted to Australia, New Caledonia, or South America. The presence of Luzuriaga-like fossils in these deposits is important for understanding Alstroemeriaceae evolution and the biogeography of genera shared between New Zealand and South America.• Methods: Leaves and a flower with in situ pollen that resemble extant Luzuriaga are described and placed phylogenetically. Geographic range information and a molecular clock model for the Alstroemeriaceae were used to investigate possible biogeographic scenarios and the influence of the new fossil on inferred divergence times.• Key results: Luzuriaga peterbannisteri Conran, Bannister, Mildenh., & D.E.Lee sp. nov. represents the first macrofossil record for Alstroemeriaceae. An associated Luzuriaga-like flower with in situ fossil pollen of Liliacidites contortus Mildenh. & Bannister sp. nov. is also described. The biogeographic analysis suggests that there have been several dispersal events across the Southern Ocean for the genus, with the fossil representing a now-extinct New Zealand lineage.• Conclusions: Luzuriaga was present in Early Miocene New Zealand, indicating a long paleogeographic history for the genus, and L. peterbannisteri strengthens biogeographic connections between South America and Australasia during the Oligocene and earliest Miocene.

Using molecular data, we recently showed that Carica papaya L. is sister to a Mexican/Guatemalan clade of two genera, Jarilla Rusby with three species and Horovitzia V.M. Badillo with one. These species are herbs or thin-stemmed trees and may be of interest for future genomics-enabled papaya breeding. Here we clarify the correct names of J. heterophylla (Cerv. ex La Llave) Rusby and J. caudata (Brandegee) Standl., which were confused in a recent systematic treatment of Jarilla (McVaugh 2001). We designate epitypes for both, provide weblinks to type specimens, a key to the species of Jarilla and Horovitzia, and notes on their habitats and distribution.

Betulaceae, with 120–150 species in six genera, are a family of Fagales that occurs mainly in the Northern Hemisphere. Previous studies of the evolution of Alnus, Betula, Carpinus, Corylus, Ostrya and Ostryopsis have relied on a relatively small number of sequence data and molecular clocks with fixed-point calibrations. We exploited GenBank to construct Betulaceae matrices of up to 900 sequence accessions and 9300 nucleotides of nuclear and plastid DNA; we also computed species consensus sequences to build 46- and 29-species matrices that strike a balance between species sampling and nucleotide sampling. Trees were rooted on Ticodendraceae and Casuarinaceae, and divergence times were inferred under relaxed and strict molecular clocks, using alternative fossil constraints. The data support the traditional two subfamilies, Betuloideae (Alnus, Betula) and Coryloideae, and show that Ostryopsis is sister to Ostrya/Carpinus. The fossil record and molecular clocks calibrated with alternating fossils indicate that the stem lineage of Betulaceae dates back to the Upper Cretaceous, the two subfamilies to the Palaeocene and the most recent common ancestors of each of the living genera to the mid- to late Miocene. A substitution rate shift in Coryloideae between 25 and 15 Mya preceded the mid-Miocene climatic optimum and may be linked to temperate niches that became available following the mid-Miocene. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172, 465–477.

SUMMARY Comparisons of closely related species are needed to understand the fine-scale dynamics of retrotransposon evolution in flowering plants. Towards this goal, we classified the long terminal repeat (LTR) retrotransposons from six diploid and one tetraploid species of Orobanchaceae. The study species are the autotrophic, non-parasitic Lindenbergia philippensis (as an out-group) and six closely related holoparasitic species of Orobanche [O. crenata, O. cumana, O. gracilis (tetraploid) and O. pancicii] and Phelipanche (P. lavandulacea and P. ramosa). All major plant LTR retrotransposon clades could be identified, and appear to be inherited from a common ancestor. Species of Orobanche, but not Phelipanche, are enriched in Ty3/Gypsy retrotransposons due to a diversification of elements, especially chromoviruses. This is particularly striking in O. gracilis, where tetraploidization seems to have contributed to the Ty3/Gypsy enrichment and led to the emergence of seven large species-specific families of chromoviruses. The preferential insertion of chromoviruses in heterochromatin via their chromodomains might have favored their diversification and enrichment. Our phylogenetic analyses of LTR retrotransposons from Orobanchaceae also revealed that the Bianca clade of Ty1/Copia and the SMART-related elements are much more widely distributed among angiosperms than previously known.

SummaryObligate mutualisms require filtering mechanisms to prevent their exploitation by opportunists, but ecological contexts and traits facilitating the evolution of such mechanisms are largely unknown. We investigated the evolution of filtering mechanisms in an epiphytic ant-plant symbiotic system in Fiji involving Rubiaceae and dolichoderine ants, using field experiments, metabolomics, X-ray micro-computed tomography (micro-CT) scanning and phylogenetics. We discovered a novel plant reward consisting of sugary sap concealed in post-anthetic flowers only accessible to Philidris nagasau workers that bite through the thick epidermis. In five of the six species of Rubiaceae obligately inhabited by this ant, the nectar glands functioned for 10 d after a flower's sexual function was over. Sugar metabolomics and field experiments showed that ant foraging tracks sucrose levels, which only drop at the onset of fruit development. Ontogenetic analyses of our focal species and their relatives revealed a 25-fold increase in nectary size and delayed fruit development in the ant-rewarding species, and Bayesian analyses of several traits showed the correlated evolution of sugar rewards and symbiosis specialization. Concealed floral nectar forestalls exploitation by opportunists (generalist ants) and stabilizes these obligate mutualisms. Our study pinpoints the importance of partner choice mechanisms in transitions from facultative to obligate mutualisms.

Few angiosperms have distinct Y chromosomes. Among those that do are Silene latifolia (Caryophyllaceae), Rumex acetosa (Polygonaceae) and Coccinia grandis (Cucurbitaceae), the latter having a male/female difference of 10% of the total genome (female individuals have a 0.85 pg genome, male individuals 0.94 pg), due to a Y chromosome that arose about 3 million years ago. We compared the sequence composition of male and female C. grandis plants and determined the chromosomal distribution of repetitive and organellar DNA with probes developed from 21 types of repetitive DNA, including 16 mobile elements. The size of the Y chromosome is largely due to the accumulation of certain repeats, such as members of the Ty1/copia and Ty3/gypsy superfamilies, an unclassified element and a satellite, but also plastome- and chondriome-derived sequences. An abundant tandem repeat with a unit size of 144 bp stains the centromeres of the X chromosome and the autosomes, but is absent from the Y centromere. Immunostaining with pericentromere-specific markers for anti-histone H3Ser10ph and H2AThr120ph revealed a Y-specific extension of these histone marks. That the Y centromere has a different make-up from all the remaining centromeres raises questions about its spindle attachment, and suggests that centromeric or pericentromeric chromatin might be involved in the suppression of recombination.