Ontogenetic origins of floral bilateral symmetry in Moringaceae (Brassicales)

Floral morphology of the 13 species of Moringa ranges from actinomorphic flowers with little hypanthium to highly zygomorphic flowers with well-developed hypanthia. Scanning electron and light microscopy were used to identify ontogenetic differences among two actinomorphic and eight zygomorphic species. All species show traces of zygomorphy between petal organogenesis and anther differentiation. At late organogenesis, zygomorphy is manifest by one petal being larger than the others, slight unidirectional maturation of the anthers, and in many species, some staminodes may be missing. At organ differentiation and beyond, the actinomorphic species show a trend toward increasing actinomorphy, whereas the zygomorphic features of early ontogeny are progressively accentuated throughout the ontogeny of the zygomorphic species. Because of the early traces of zygomorphy throughout the family, ontogeny in Moringa does not resemble that known from the sister taxon Caricaceae, which has flowers that are actinomorphic throughout ontogeny. Great intraspecific variation was found in floral plan in the actinomorphic-flowered species in contrast to the zygomorphic species. Each of the main clades in the family is distinguished by at least one feature of floral ontogeny. In general, ontogenetic differences that are congruent with deeper phylogenetic splits tend to occur earlier in ontogeny than those congruent with more recent divergences.     

Specific Duplication and Dorsoventrally Asymmetric Expression Patterns of Cycloidea-Like Genes in Zygomorphic Species of Ranunculaceae

Floral bilateral symmetry (zygomorphy) has evolved several times independently in angiosperms from radially symmetrical (actinomorphic) ancestral states. Homologs of the Antirrhinum majus Cycloidea gene (Cyc) have been shown to control floral symmetry in diverse groups in core eudicots. In the basal eudicot family Ranunculaceae, there is a single evolutionary transition from actinomorphy to zygomorphy in the stem lineage of the tribe Delphinieae. We characterized Cyc homologs in 18 genera of Ranunculaceae, including the four genera of Delphinieae, in a sampling that represents the floral morphological diversity of this tribe, and reconstructed the evolutionary history of this gene family in Ranunculaceae. Within each of the two RanaCyL (Ranunculaceae Cycloidea-like) lineages previously identified, an additional duplication possibly predating the emergence of the Delphinieae was found, resulting in up to four gene copies in zygomorphic species. Expression analyses indicate that the RanaCyL paralogs are expressed early in floral buds and that the duration of their expression varies between species and paralog class. At most one RanaCyL paralog was expressed during the late stages of floral development in the actinomorphic species studied whereas all paralogs from the zygomorphic species were expressed, composing a species-specific identity code for perianth organs. The contrasted asymmetric patterns of expression observed in the two zygomorphic species is discussed in relation to their distinct perianth architecture.     

Support for the predictions of the pollinator-mediated stabilizing selection hypothesis

Aims Floral traits are frequently used in traditional plant systematics because of their assumed constancy. One potential reason for the apparent constancy of flower size is that effective pollen transfer between flowers depends on the accuracy of the physical fit between the flower and pollinator. Therefore, flowers are likely to be under stronger stabilizing selection for uniform size than vegetative plant parts. Moreover, as predicted by the pollinator-mediated stabilizing selection (PMSS) hypothesis, an accurate fit between flowers and their pollinators is likely to be more important for specialized pollination systems as found in many species with bilaterally symmetric (zygomorphic) flowers than for species with radially symmetric (actinomorphic) flowers.Methods In a comparative study of 15 zygomorphic and 13 actinomorphic species in Switzerland, we tested whether variation in flower size, among and within individuals, is smaller than variation in leaf size and whether variation in flower size is smaller in zygomorphic compared to actinomorphic species.Important findings Indeed, variation in leaf length was significantly larger than variation in flower length and width. Within-individual variation in flower and leaf sizes did not differ significantly between zygomorphic and actinomorphic species. In line with the predictions of the PMSS, among-individual variation in flower length and flower width was significantly smaller for zygomorphic species than for actinomorphic species, while the two groups did not differ in leaf length variation. This suggests that plants with zygomorphic flowers have undergone stronger selection for uniform flowers than plants with actinomorphic flowers. This supports that the relative uniformity of flowers compared to vegetative structures within species, as already observed in traditional plant systematics, is, at least in part, a consequence of the requirement for effective pollination.     

Natural selection on Erysimum mediohispanicum flower shape: insights into the evolution of zygomorphy

Paleontological and phylogenetic studies have shown that floral zygomorphy (bilateral symmetry) has evolved independently in several plant groups from actinomorphic (radially symmetric) ancestors as a consequence of strong selection exerted by specialized pollinators. Most studies focused on unraveling the developmental genetics of flower symmetry, but little is known about the adaptive significance of intraspecific flower shape variation under natural conditions. We provide the first evidence for natural selection favoring zygomorphy in a wild population of Erysimum mediohispanicum (Brassicaceae), a plant showing extensive continuous variation in flower shape, ranging from actinomorphic to zygomorphic flowers. By using geometric morphometric tools to describe flower shape, we demonstrate that plants bearing zygomorphic flowers received more pollinator visits and had the highest fitness, measured not only by the number of seeds produced per plant but also by the number of seeds surviving to the juvenile stage. This study provides strong evidence for the existence of significant fitness differences associated with floral shape variation in E. mediohispanicum, thus illuminating a pathway for the evolution of zygomorphy in natural populations.     

The influence of floral symmetry,dependence on pollinators and pollination generalization on flower size variation

Background and Aims

The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared with actinomorphic flowers. However, the degree of ecological generalization and of dependence on pollinators varies greatly among species of both flower symmetry types and this may also affect flower size variation.

Methods

Data on 43 species from two contrasting communities (one alpine and one lowland community) were used to test the relationships and interactions between flower size phenotypic variation, floral symmetry, ecological pollination generalization and species'' dependence on pollinators.

Key Results

Contrary to what was expected, higher flower size variation was found in zygomorphic than in actinomorphic species in the lowland community, and no difference in flower size variation was found between symmetry types in the alpine community. The relationship between floral symmetry and flower size variation depended on ecological generalization and species'' dependence on pollinators, although the influence of ecological generalization was only detected in the alpine community. Zygomorphic species that were highly dependent on pollinators and that were ecologically specialized were less variable in flower size than ecologically generalist and selfing zygomorphic species, supporting the pollinator-mediated stabilizing selection hypothesis. However, these relationships were not found in actinomorphic species, probably because they are not dependent on any particular pollinator for efficient pollination and therefore their flower size always shows moderate levels of variation.

Conclusions

The study suggests that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species'' dependence on pollinators.     

Floral development and evolution of capitulum structure in Anacyclus (Anthemideae,Asteraceae)

Background and Aims

Most of the diversity in the pseudanthia of Asteraceae is based on the differential symmetry and sexuality of its flowers. In Anacyclus, where there are (1) homogamous capitula, with bisexual, mainly actinomorphic and pentamerous flowers; and (2) heterogamous capitula, with peripheral zygomorphic, trimerous and long-/short-rayed female flowers, the floral ontogeny was investigated to infer their origin.

Methods

Floral morphology and ontogeny were studied using scanning electron microscope and light microscope techniques

Key Results

Disc flowers, subtended by paleae, initiate acropetally. Perianth and androecium initiation is unidirectional/simultaneous. Late zygomorphy occurs by enlargement of the adaxial perianth lobes. In contrast, ray flowers, subtended by involucral bracts, initiate after the proximal disc buds, breaking the inflorescence acropetal pattern. Early zygomorphy is manifested through the fusion of the lateral and abaxial perianth lobes and the arrest of the adaxials. We report atypical phenotypes with peripheral ‘trumpet’ flowers from natural populations. The peripheral ‘trumpet’ buds initiate after disc flowers, but maintain an actinomorphic perianth. All phenotypes are compared and interpreted in the context of alternative scenarios for the origin of the capitulum and the perianth identity.

Conclusions

Homogamous inflorescences display a uniform floral morphology and development, whereas the peripheral buds in heterogamous capitula display remarkable plasticity. Disc and ray flowers follow different floral developmental pathways. Peripheral zygomorphic flowers initiate after the proximal actinomorphic disc flowers, behaving as lateral independent units of the pseudanthial disc from inception. The perianth and the androecium are the most variable whorls across the different types of flowers, but their changes are not correlated. Lack of homology between hypanthial appendages and a calyx, and the perianth double-sided structure are discussed for Anacyclus together with potential causes of its ray flower plasticity.     

A pollinators' eye view of a shelter mimicry system

Background and Aims

‘Human-red’ flowers are traditionally considered to be rather unpopular with bees, yet some allogamous species in the section Oncocyclus (genus Iris, Iridaceae) have evolved specialized interactions with their pollinators, a narrow taxonomic range of male solitary bees. The dark-red, tubular flowers of these irises are nectarless but provide protective shelters (i.e. a non-nutritive form of reward) primarily to male solitary bees (Apidae, Eucerini) that pollinate the flowers while looking for a shelter. An earlier study on orchids suggested that species pollinated predominantly by male solitary bees produce significantly larger amounts and larger numbers of different n-alkenes (unsaturated cuticular hydrocarbons). Whether or not this also applies to the Oncocyclus irises and whether pollinators are attracted by specific colours or scents of these flowers is unknown.

Methods

Using Iris atropurpurea, recording of pollinator preferences for shelters with different spatial parameters was combined with analyses of floral colours (by spectrophotometry) and scents (by gas chromatography–mass spectrometry) to test the hypotheses that (a) pollinators significantly prefer floral tunnels facing the rising sun (floral heat-reward hypothesis), and that (b) flowers pollinated predominantly by male solitary bees produce significantly larger amounts and larger numbers of unsaturated cuticular hydrocarbons (n-alkenes) in their floral scent (preadaptation to sexual-deception hypothesis).

Key Results

Male bees do not significantly prefer shelters facing the rising sun or with the presence of high absolute/relative amounts and numbers of n-alkenes in the floral scent.

Conclusions

The results suggest that the flowers of I. atropurpurea probably evolved by pollinator-mediated selection acting primarily on floral colours to mimic large achromatic (‘bee-black’) protective shelters used preferentially by male solitary bees, and that pollinator visits are presumably not the result of an odour-based sexual stimulation or motivated by an increased morning floral heat reward in tunnels facing the rising sun.     

Phylogeny and classification of Ranunculales: Evidence from four molecular loci and morphological data

Previous phylogenetic analyses of Ranunculales, which have mostly been focused on an individual family and were based on molecular data alone, have recovered three main clades within the order. However, support for relationships among these three clades was weak. Earlier hypotheses were often hampered by limited taxon sampling; to date less than one-tenth of the genera in the order have been sampled. In this study, we used a greatly enlarged taxon sampling (105 species, representing 99 genera of all seven families in the order). Our study is, furthermore, the first to employ morphology (65 characters) in combination with sequence data from four genomic regions, including plastid rbcL, matK and trnL-F, and nuclear ribosomal 26S rDNA to reconstruct phylogenetic relationships within Ranunculales. Maximum parsimony and Bayesian inference were performed on the individual and combined data sets. Our analyses concur with those of previous studies, but in most cases provide stronger support and better resolution for relationships among the three main clades retrieved. The first, comprised solely of the monogeneric family Eupteleaceae, is the earliest-diverging lineage. The second clade is composed exclusively of taxa of Papaveraceae, which is sister to the third clade, the core Ranunculales, comprising the other five families of the order. Circaeasteraceae and Lardizabalaceae form a strongly supported clade. Pteridophyllum is supported as sister to Hypecoum, contradicting the viewpoint that the former is the earliest-diverging genus in Papaveraceae. Glaucidium is basalmost in Ranunculaceae. Within this phylogenetic framework, the evolution of selected characters is inferred and diagnostic morphological characters at different taxonomic levels are identified and discussed. Based on both morphological and molecular evidence, a classification outline for Ranunculales is presented, including the proposal of two new subfamilies, Menispermoideae and Tinosporoideae in Menispermaceae and a new tribe, Callianthemeae, for the genus Callianthemum (Ranunculaceae).     

Altered expression patterns of TCP and MYB genes relating to the floral developmental transition from initial zygomorphy to actinomorphy in Bournea (Gesneriaceae)

The shift from zygomorphy to actinomorphy has been intensively studied in molecular genetic model organisms. However, it is still a key challenge to explain the great morphological diversity of derived actinomorphy in angiosperms, since different underlying mechanisms may be responsible for similar external morphologies. Bournea (Gesneriaceae) is of particular interest in addressing this question, as it is a representative of primarily derived actinomorphy characteristic of a unique developmental transition from zygomorphy to actinomorphic flowers at anthesis. Using RNA in situ hybridization, the expression patterns were investigated of three different Bournea orthologues of TCP and MYB genes that have been shown to control floral symmetry in model species. Here, it is shown that the initial zygomorphic pattern in Bournea is likely a residual zygomorphy resulting from conserved expression of the adaxial (dorsal) identity gene BlCYC1. As a key novel event, the late downregulation of BlCYC1 and BlRAD and the correlative changes in the late specific expression of the abaxial (ventral) identity gene BlDIV should be responsible for the origin of the derived actinomorphy in Bournea. These results further indicate that there might be diverse pathways in the origin and evolution of derived actinomorphy through modifications of pre-existing zygomorphic developmental programs under dynamics of regulatory networks.     

The role of pollinator diversity in the evolution of corolla-shape integration in a pollination-generalist plant clade

Flowers of animal-pollinated plants are integrated structures shaped by the action of pollinator-mediated selection. It is widely assumed that pollination specialization increases the magnitude of floral integration. However, empirical evidence is still inconclusive. In this study, we explored the role of pollinator diversity in shaping the evolution of corolla-shape integration in Erysimum, a plant genus with generalized pollination systems. We quantified floral integration in Erysimum using geometric morphometrics and explored its evolution using phylogenetic comparative methods. Corolla-shape integration was low but significantly different from zero in all study species. Spatial autocorrelation and phylogenetic signal in corolla-shape integration were not detected. In addition, integration in Erysimum seems to have evolved in a way that is consistent with Brownian motion, but with frequent convergent evolution. Corolla-shape integration was negatively associated with the number of pollinators visiting the flowers of each Erysimum species. That is, it was lower in those species having a more generalized pollination system. This negative association may occur because the co-occurrence of many pollinators imposes conflicting selection and cancels out any consistent selection on specific floral traits, preventing the evolution of highly integrated flowers.     

Evolution of perianth and stamen characteristics with respect to floral symmetry in Ranunculales

BACKGROUND AND AIMS: Floral symmetry presents two main states in angiosperms, namely polysymmetry and monosymmetry. Monosymmetry is thought to have evolved several times independently from polysymmetry, possibly in co-adaptation with specialized pollinators. Monosymmetry commonly refers to the perianth, even though associated androecium modifications have been reported. The evolution of perianth symmetry is examined with respect to traits of flower architecture in the Ranunculales, the sister group to all other eudicots, which present a large diversity of floral forms. METHODS: Characters considered were perianth merism, calyx, corolla and androecium symmetry, number of stamens and spurs. Character evolution was optimized on a composite phylogenetic tree of Ranunculales using maximum parsimony. KEY RESULTS: The ancestral state for merism could not be inferred because the basalmost Eupteleaceae lack a perianth and have a variable number of stamens. The Papaveraceae are dimerous, and the five other families share a common trimerous ancestor. Shifts from trimery to dimery (or reverse) are observed. Pentamery evolved in Ranunculaceae. Ranunculales except Eupteleaceae, present a polysymmetric ancestral state. Monosymmetry evolved once within Papaveraceae, Ranunculaceae and Menispermaceae (female flowers only). Oligandry is the ancestral state for all Ranunculales, and polyandry evolved several times independently, in Papaveraceae, Menispermaceae, Berberidaceae and Ranunculaceae, with two reversions to oligandry in the latter. The ancestral state for androecium symmetry is ambiguous for the Ranunculales, while polysymmetry evolved immediately after the divergence of Eupteleaceae. A disymmetric androecium evolved in Papaveraceae. The ancestral state for spurs is none. Multiple spurs evolved in Papaveraceae, Berberidaceae and Ranunculaceae, and single spurs occur in Papaveraceae and Ranunculaceae. CONCLUSIONS: The evolution of symmetry appears disconnected from changes in merism and stamen number, although monosymmetry never evolved in the context of an open ground plan. In bisexual species, monosymmetry evolved coincidently with single spurs, allowing us to propose an evolutionary scenario for Papaveraceae.     

Floral zygomorphy, the recurring evolution of a successful trait

The flowers of the primitive angiosperm plants were radially symmetrical (actinomorphic). Flowers with bilateral symmetry (zygomorphic) evolved in several clades independently as an adaptation to specialized methods of pollination and played an important role in the diversification of flowering plants. In the model species Antirrhinum majus (snapdragon), the related genes CYCLOIDEA (CYC) and DICHOTOMA (DICH) are key in the development of this trait. This raises the question of whether they played a role in the evolution of floral bilateral symmetry. To address this, the evolution of CYC in relation to the evolution of zygomorphy is being investigated. Phylogenetic and functional analyses of CYC-like genes are being carried out in groups either closely related to Antirhinum or in families where zygomorphy evolved as an independent event. In addition, the origin of zygomorphy is being studied by comparing the function of CYC-like genes in species with zygomorphic flowers with their function in species with radially symmetrical flowers.     

Chemical constituents from the aerial parts of Meconopsis horridula (Papaveraceae)

Chemical investigation of the aerial parts of Meconopsis horridula led to the isolation and structural identification of nine flavonoids, two alkaloids and five terpenoids. Their structures were determined by comparison of ¹H and ¹³C NMR data with those reported in literature. The discovery of alkaloid cavidilinine (11) and two pentacyclic triterpenoids (15 and 16) from M. horridula provides evidence to support the view that Fumarioideae and Papaveroideae should be combined into a single family Papaveraceae.     

Floral structure and development in the monoecious palm Gaussia attenuata (Arecaceae; Arecoideae)

Background and Aims

Sexual dimorphism, at both the flower and plant level, is widespread in the palm family (Arecaceae), in contrast to the situation in angiosperms as a whole. The tribe Chamaedoreeae is of special interest for studies of the evolution of sexual expression since dioecy appears to have evolved independently twice in this group from a monoecious ancestor. In order to understand the underlying evolutionary pathways, it is important to obtain detailed information on flower structure and development in each of the main clades.

Methods

Dissection and light and scanning electron microscopy were performed on developing flowers of Gaussia attenuata, a neotropical species belonging to one of the three monoecious genera of the tribe.

Key Results

Like species of the other monoecious genera of the Chamaedoreeae (namely Hyophorbe and Synechanthus), G. attenuata produces a bisexual flower cluster known as an acervulus, consisting of a row of male flowers with a basal female flower. Whereas the sterile androecium of female flowers terminated its development at an early stage of floral ontogeny, the pistillode of male flowers was large in size but with no recognizable ovule, developing for a longer period of time. Conspicuous nectary differentiation in the pistillode suggested a possible role in pollinator attraction.

Conclusions

Gaussia attenuata displays a number of floral characters that are likely to be ancestral to the tribe, notably the acervulus flower cluster, which is conserved in the other monoecious genera and also (albeit in a unisexual male form) in the dioecious genera (Wendlandiella and a few species of Chamaedorea). Comparison with earlier data from other genera suggests that large nectariferous pistillodes and early arrest in staminode development might also be regarded as ancestral characters in this tribe.     

花对称性的研究进展

花对称性(floral symmetry)是被子植物花部结构的典型特性之一,主要有辐射对称和两侧对称两种形式。被子植物初始起源的花为辐射对称,而两侧对称的花则是由辐射对称的花演变而来。两侧对称的花部结构是被子植物进化过程中的一个关键的革新,被认为是物种形成和分化的关键推动力之一。近年来有关花对称性的形成和进化机制的研究在植物学科的不同领域均取得了长足的进展。本文综述了花对称性在发育生物学、传粉生物学、生殖生态学及分子生物学等方面的研究进展。两侧对称形成于被子植物花器官发育的起始阶段,随后贯穿整个花器官发育过程或者出现在花器官发育后期的不同阶段。花器官发育过程中一种或多种类型器官的败育以及特异性花器官结构的形成是两侧对称形成的主要原因。研究表明,在传粉过程的不同阶段,花对称性均会受到传粉昆虫介导的选择作用。相比辐射对称的花,两侧对称的花提高了特异性传粉者的选择作用,增加了花粉落置的精确性,进而确保了其生殖成功。花对称性的分子机理已经在多种双子叶植物中进行了深入的研究。现有的证据表明,CYC同源基因在花对称性的分子调控方面起着非常重要的作用。花对称性在被子植物进化过程中是如何起源,与其他花部构成之间是否协同作用,一些不符合一般模式的科属其花对称性的形成机制等都是今后要进一步研究的命题。     

Phylogenetic relationships among arecoid palms (Arecaceae: Arecoideae)

Background and Aims

The Arecoideae is the largest and most diverse of the five subfamilies of palms (Arecaceae/Palmae), containing >50 % of the species in the family. Despite its importance, phylogenetic relationships among Arecoideae are poorly understood. Here the most densely sampled phylogenetic analysis of Arecoideae available to date is presented. The results are used to test the current classification of the subfamily and to identify priority areas for future research.

Methods

DNA sequence data for the low-copy nuclear genes PRK and RPB2 were collected from 190 palm species, covering 103 (96 %) genera of Arecoideae. The data were analysed using the parsimony ratchet, maximum likelihood, and both likelihood and parsimony bootstrapping.

Key Results and Conclusions

Despite the recovery of paralogues and pseudogenes in a small number of taxa, PRK and RPB2 were both highly informative, producing well-resolved phylogenetic trees with many nodes well supported by bootstrap analyses. Simultaneous analyses of the combined data sets provided additional resolution and support. Two areas of incongruence between PRK and RPB2 were strongly supported by the bootstrap relating to the placement of tribes Chamaedoreeae, Iriarteeae and Reinhardtieae; the causes of this incongruence remain uncertain. The current classification within Arecoideae was strongly supported by the present data. Of the 14 tribes and 14 sub-tribes in the classification, only five sub-tribes from tribe Areceae (Basseliniinae, Linospadicinae, Oncospermatinae, Rhopalostylidinae and Verschaffeltiinae) failed to receive support. Three major higher level clades were strongly supported: (1) the RRC clade (Roystoneeae, Reinhardtieae and Cocoseae), (2) the POS clade (Podococceae, Oranieae and Sclerospermeae) and (3) the core arecoid clade (Areceae, Euterpeae, Geonomateae, Leopoldinieae, Manicarieae and Pelagodoxeae). However, new data sources are required to elucidate ambiguities that remain in phylogenetic relationships among and within the major groups of Arecoideae, as well as within the Areceae, the largest tribe in the palm family.     

The evolution of staminodes in angiosperms: patterns of stamen reduction, loss, and functional re-invention

Stamens that have lost their primary function of pollen production, or staminodes, occur uncommonly within angiosperms, but frequently fulfill important secondary floral functions. The phylogenetic distribution of staminodes suggests that they typically arise during evolutionary reduction of the androecium. Differences in the genetic control and patterns of stamen loss between actinomorphic and zygomorphic flowers shape staminode development. In clades with actinomorphic flowers, staminodes generally replace an entire stamen whorl and staminode loss seems irreversible. In contrast, in clades with zygomorphic flowers staminodes evolve from a subset of the stamens in a whorl and staminodes can reappear in a lineage after being lost (e.g., Cheloneae, Scrophulariaceae). If staminodes do not adopt new functions during androecium reduction they are lost quickly, so that nonfunctional staminodes appear only in recently derived taxa. Alternatively, when staminodes assume new floral roles, either directly or indirectly after a nonfunctional period, they can become integral floral components which perpetuate within clades (e.g., Orchidaceae). Indirect evolution of staminode function allows greater flexibility of function by allowing staminodes to take over roles not performed by stamens, such as involvement in mechanisms to prevent self-pollination and mechanisms of explosive pollination. Multifunctional staminodes characterize lineages with universal or widespread staminodes.     

Phylogeny of the cycads based on multiple single-copy nuclear genes: congruence of concatenated parsimony,likelihood and species tree inference methods

Background and aims

Despite a recent new classification, a stable phylogeny for the cycads has been elusive, particularly regarding resolution of Bowenia, Stangeria and Dioon. In this study, five single-copy nuclear genes (SCNGs) are applied to the phylogeny of the order Cycadales. The specific aim is to evaluate several gene tree–species tree reconciliation approaches for developing an accurate phylogeny of the order, to contrast them with concatenated parsimony analysis and to resolve the erstwhile problematic phylogenetic position of these three genera.

Methods

DNA sequences of five SCNGs were obtained for 20 cycad species representing all ten genera of Cycadales. These were analysed with parsimony, maximum likelihood (ML) and three Bayesian methods of gene tree–species tree reconciliation, using Cycas as the outgroup. A calibrated date estimation was developed with Bayesian methods, and biogeographic analysis was also conducted.

Key Results

Concatenated parsimony, ML and three species tree inference methods resolve exactly the same tree topology with high support at most nodes. Dioon and Bowenia are the first and second branches of Cycadales after Cycas, respectively, followed by an encephalartoid clade (Macrozamia–Lepidozamia–Encephalartos), which is sister to a zamioid clade, of which Ceratozamia is the first branch, and in which Stangeria is sister to Microcycas and Zamia.

Conclusions

A single, well-supported phylogenetic hypothesis of the generic relationships of the Cycadales is presented. However, massive extinction events inferred from the fossil record that eliminated broader ancestral distributions within Zamiaceae compromise accurate optimization of ancestral biogeographical areas for that hypothesis. While major lineages of Cycadales are ancient, crown ages of all modern genera are no older than 12 million years, supporting a recent hypothesis of mostly Miocene radiations. This phylogeny can contribute to an accurate infrafamilial classification of Zamiaceae.