Structure and development of bracteal nectary glands in Aphelandra (Acanthaceae)

A survey of bracteal (extrafloral) nectaries in species of Aphelandra (Acanthaceae) reveals substantial diversity. Each bracteal nectary is an aggregate of individual glands that vary in number, size, and structure among species. Glands contain three cell layers: a palisade-like secretory cell layer, a one-to-many-celled intermediate layer with thickened cell walls, and a foot layer. Members of the A. pulcherrima complex have one of two distinct gland types: relatively small glands with a single-celled intermediate layer or larger glands that have a multicellular intermediate layer. Nectaries composed of small glands are patches of many (>50) glands, whereas those composed of large glands are patches of < 10 glands. Four outgroup species have bracteal nectaries of numerous small glands with pluricellular intermediate layers. Glands of all three types are initiated as single enlarged protodermal cells, and all undergo similar early periclinal divisions; the large-gland type shows greater subsequent enlargement with many more anticlinal divisions. The bracteal nectar glands are interpreted to be homologous with simpler glandular trichomes, and mark a monophyletic lineage within Aphelandra. Comparisons with outgroup species show that both nectary types in the A. pulcherrima complex have diverged from an ancestral condition of numerous small glands with pluricellular intermediate layers. Use of the ontogenetic criterion to polarize gland type within the A. pulcherrima complex would yield erroneous results because evolution has apparently involved a developmental truncation with loss of cell divisions in the intermediate layer of small glands. Comparable nectar glands in more distant taxa are interpreted as remarkable cases of convergent evolution, perhaps from similar trichome precursors.     

Floral anatomy of Bromeliaceae, with particular reference to the evolution of epigyny and septal nectaries in commelinid monocots

Floral anatomy is described in ten genera of Bromeliaceae, including three members of subfamily Bromelioideae, three Tillandsioideae, and four genera of the polyphyletic subfamily Pitcairnioideae (including Brocchinia, the putatively basal genus of Bromeliaceae). Bromeliaceae are probably unique in the order Poales in possessing septal nectaries and epigynous or semi-epigynous flowers. Evidence presented here from floral ontogeny, vasculature, and the relative positions of nectary and ovules indicates that there could have been one or more reversals to apparent hypogyny in Bromeliaceae, although this hypothesis requires a better-resolved phylogeny. Such evolutionary reversals probably evolved in response to specialist pollinators, and in conjunction with other aspects of floral morphology of Bromeliaceae, such as the petal appendages of some species. The ovary is initiated in an inferior position even in semi-epigynous or hypogynous species. The ovary of all so-called hypogynous Bromeliaceae is actually semi-inferior, because the septal nectary is infralocular; in these species the nectaries have a labyrinthine surface and many vascular bundles. Brocchinia differs from most other fully epigynous species in that each carpel is secretory at the apex and reproductive, rather than secretory, at the base.     

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.     

Floral development and anatomy of Dirachma socotrana, (Dirachmaceae): a controversial member of the Rosales

The floral development and anatomy of Dirachma has been investigated with SEM and LM to discuss the relationship of Dirachmaceae with putative sister taxa (e.g. Rhamnaceae, Malvaceae, Barbeyaceae, Elaeagnaceae) on the basis of morphological synapomorphies. Flowers are initiated in axillary position on terminal branches. An epicalyx consisting of six to eight bracteoles surrounds the valvate calyx. Petal initiation is strongly retarded and primordia arise independently opposite the stamen primordia. The carpels arise independently and become weakly fused at the base; a single ovule develops in an axile position. A hypanthium develops by interprimordial growth between petals and stamens. Nectaries arise in a pouch and are covered with trichomes positioned on a protuberance at the base of the petal. It is suggested that the solitary flowers are derived from compound cymose inflorescences. Comparison between Dirachma and species of Rhamnaceae demonstrates striking similarities in floral structure and anatomy. However, several characters are unique to Dirachma and support a family Dirachmaceae separate from Rhamnaceae.We thank Frieda Christie for technical assistance with the SEM and LM preparations. We very much appreciate the constructive comments of Peter Endress and Paula Rudall.     

Evolution of lamina anatomy in the palm family (Arecaceae)

The unique properties of tree building in Arecaceae strongly constrain their architectural lability. Potentially compensating for this limitation, the extensive diversification of leaf anatomical structure within palms involves many characters whose alternate states may confer disparate mechanical or physiological capabilities. In the context of a recent global palm phylogeny, we analyzed the evolution of 10 such lamina anatomical characters and leaf morphology of 161 genera, conducting parsimony and maximum likelihood ancestral state reconstructions, as well as tests of correlated evolution. Lamina morphology evolves independently from anatomy. Although many characters do optimize as synapomorphic for major clades, anatomical evolution is highly homoplasious. Nevertheless, it is not random: analyses indicate the recurrent evolution of different cohorts of correlated character states. Notable are two surface layer (epidermis and hypodermis) types: (1) a parallel-laminated type of rectangular epidermal cells with sinuous anticlinal walls, with fibers present in the hypodermis and (2) a cross-laminated type of hexagonal cells in both layers. Correlated with the cross-laminated type is a remarkable decrease in the volume fraction of fibers, accompanied by changes in the architecture and sheath cell type of the transverse veins. We discuss these and other major patterns of anatomical evolution in relation to their biomechanical and ecophysiological significance.     

Floral ontogeny in Dipterygeae (Fabaceae) reveals new insights into one of the earliest branching tribes in papilionoid legumes

Flowers of Dipterygeae (Fabaceae, Papilionoideae) exhibit an unusual petaloid calyx. The two adaxial sepals are large and petaloid, and the three abaxial sepals form a three‐toothed lobe. The goal of this study was to elucidate the ontogenetic pathways of this peculiar calyx in light of the floral development of the three genera that comprise the tribe. Floral buds of Dipteryx alata, Pterodon pubescens and Taralea oppositifolia were analysed using scanning electron microscopy and light microscopy. The order of bracteole and sepal initiation varies among the species. The androecium is asymmetric. The carpel cleft is positioned to the right or to the left, and is opposite the adaxial antepetalous stamen. The peculiarity of the calyx becomes noticeable in the intermediate stages of floral development. It results from the differential growth of the sepal primordia, in which the abaxial and lateral primordia remain diminutive during floral development, compared with the adaxial ones that enlarge and elongate. Bracteoles, abaxial sepals, petals and anthers are appendiculate, except in T. oppositifolia, in which the appendices were not found in bracteoles or anthers. These appendices comprise secretory canals or cavities. Considering that the ontogenetic pathway for the formation of the petaloid calyx is similar and exclusive for Dipterygeae, it might be a potential synapomorphy for the group, with the presence of secretory canals in the appendices of abaxial and lateral sepals and petals. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174 , 529–550.     

Comparative floral structure and systematics in the Asian palm genus Rhapis (Arecaceae,Coryphoideae)

A comparative study of the floral structure in the species of the genus Rhapis (Arecaceae, Coryphoideae, Rhapidinae) is presented. Flowers are mainly unisexual, with three sepals, three petals, 6 stamens or staminodes and three carpels or carpellodes. Some evidences of basal congenital and apical postgenital fusion of the carpels, first time reported in the genus, were observed in the gynoecium. Ovules are basally attached and crassinucellate; they appear to be slightly anatropous. The morphology of the filaments suggests a division of the species into two groups: Rhapis excelsa and R. subtilis exhibit thick and keeled filaments, whereas R. gracilis, R. humilis, R. laosensis, R. micrantha and R. multifida have slender, non-keeled filaments. Relationships of Rhapis with the rest of the genera of Rhapidinae are inferred on the light of floral structure.     

Floral anatomy in Dypsis (Arecaceae–Areceae): a case of complex synorganization and stamen reduction

Male (staminate) flowers of Dypsis possess either six or three stamens and/or staminodes, in contrast to most other palms, in which the basic stamen number is six (although polyandry is also common in palms). Significant variation among the tristaminate forms, both in stamen morphology and stamen position with respect to the perianth parts, indicates that stamen reduction from six to three has occurred more than once, and possibly several times within Dypsis. A few species include teratological forms with zygomorphic flowers; for example, Dypsis lantzeana normally possesses three antesepalous stamens, but in some specimens only the median outer (abaxial) stamen is expressed, perhaps indicating incipient zygomorphy correlated with complex synorganization. Inclusion of earlier historic genera such as Neophloga and Chrysalidocarpus within a broadly circumscribed Dypsis appears to be justified, although the informal taxonomic groupings within Dypsis require review, in particular the taxonomic significance of the different types of anther morphology. The discovery here that adnation of staminodes to the pistillode (complex synorganization) occurs in species other than D. mirabilis opens further questions about the taxonomic utility of this character in Dypsis, in which stamen/staminode development and adnation are apparently unusually labile. Such androecial–gynoecial adnation is otherwise rare in palms, as also in other monocots, in which probably the best‐known example occurs in orchids. Septal nectaries are present in some, but not all, staminate flowers in species of Dypsis. Dypsis bejofo is exceptional in that in staminate flowers the pistillode is distally bulbous and bears three prominent modified supralocular septal nectaries. Female (pistillate) flowers in Dypsis are syncarpous, normally pseudomonomerous (as in many other Arecoideae), and possess septal nectaries that effectively delimit the carpel margins and indicate insect pollination. There is a central solid transmitting tissue that extends from the placenta to three stylar canals. The stylar canals of the two sterile carpels are apparently functional, in addition to that of the fertile carpel. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143 , 115?133.     

Generic limits in Polygonurn and related genera (Polygonaceae) on the basis of floral characters

In order to investigate the taxonomic value of a number of characters in the elucidation of relationships within the collective genus Polygonum L., and segregate genera Atraphaxis L., Calligonum L., Pteropyrum Jaub. & Spach., Oxygonum Burch., Fagopyrum Mill., Harpagocarpus Hutch. & Dandy and Polygonella Michx., 83 species of the tribe Polygoneae emend. Jaretzky were studied. The following floral characters were examined: stamen number, insertion and external morphology; structure and morphology of the floral nectaries; vasculature and surface morphology of the tepals.
Problems in floral morphology in Polygonaceae are discussed, together with relationships within the Family. The tribal division proposed by Haraldson (1978) is supported, but a new and different delimitation of genera is proposed. The present data support a division of Polygonum L. sensu lato and its related taxa into two tribes: Polygoneae (containing Polygonum L. sensu stricto, Fallopia Adans., Oxygonum Burch., Pteropyrum Jaub. & Sparh., Atraphaxis L. and Calligonum L.), and Persicarieae (containing Fagopyrum Mill., Harpagocarpus Hutch. & Dandy, Persicaria Mill. and Koenigia L.). The genus Reynoutria Houtt. is included as a section of Fallopia Adans.; Bislorta Mill., Aconogonon Reichenb. and Tovara Adans. are included within Persicaria Mill.
A number of new combinations are proposed in Persicaria and Fallopia .     

Floral anatomy of Thomandersia (Lamiales), with particular reference to the nature of the retinaculum and extranuptial nectaries

Thomandersia is an isolated genus that is currently unplaced in Lamiales. In the past it has been classified in Acanthaceae or Pedaliaceae, on the basis of intuitive assessments of a limited number of morphological characters. Recent molecular sequenced-based phylogenies have suggested a relationship to Bignoniaceae, Schlegeliaceae or Verbenaceae. Here we present new observations of the floral anatomy of Thomandersia , with particular emphasis on the structure of the retinaculum, a character shared with Acanthaceae, and calyx nectaries, which may be shared with other families in Lamiales. The morphological and anatomical characters of Thomandersia are discussed in the context of recent phylogenetic hypotheses for Lamiales, with the aim of identifying potential primary and secondary homologies between Thomandersia and related families in Lamiales. We find that Thomandersia shares a range of characters with each of the families to which it might be sister-group, and that some of these primary homologies must therefore be homoplastic. In particular, if the topology based on molecular sequence data is correct, the retinacula of Thomandersia and Acanthaceae are homoplastic and represent an example of parallel morphological evolution.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 469–482.     

Genetic structure among morphotypes of the endangered Brazilian palm Euterpe edulis Mart (Arecaceae)

Euterpe edulis (Arecaceae) Mart has high ecological and economic importance providing food resources for more than 58 species of birds and 20 species of mammals, including humans. E. edulis is the second most exploited nontimber product from Brazilian Atlantic Forest. Due to overexploitation and destruction of habitats, E. edulis is threatened by extinction. Euterpe edulis populations have large morphological variations, with individuals having green, red, or yellow leaf sheath. However, no study has related phenotypic distinctions between populations and their levels of genetic structure. Thus, this study aimed to evaluate the diversity and genetic structure of different E. edulis morphotypes. We sampled 250 adult individuals in eight populations with the different morphotypes. Using 14 microsatellite markers, we access genetic diversity through population genetic parameters calculated in the GenAlex program and the diveRsity package in R. We used the Wilcoxon test to verify population bottlenecks and the genetic distance of Nei and Bayesian analysis for genetic clusters. The eight populations showed low allele richness, low observed heterozygosity, and high inbreeding values (f). In addition, six of the eight populations experienced genetic bottlenecks, which would partly explain the low genetic diversity in populations. Cluster analysis identified two clusters (K = 2), with green morphotype genetically distinguishing from yellow and red morphotypes. Thus, we show, for the first time, a strong genetic structure among E. edulis morphotypes even for geographically close populations.     

芭蕉科花蜜腺形态比较：兼论其与传粉者的关系（英文）

对狭义芭蕉科3个属的代表性种芭蕉(Musa basjoo)、象腿蕉(Ensete glaucum)和地涌金莲(Musella lasiocarpa)的花蜜腺形态进行了比较研究。结果表明它们的蜜腺属于隔膜蜜腺。雌花的蜜腺着生于子房的上部,胚珠的上方;雄花蜜腺占据了整个败育子房的位置。蜜腺结构由许多腔道组成,这些腔道在横切面上呈现出复杂的发散式迷宫状结构。这3种植物花蜜腺的栅栏状表皮细胞、维管束和蜜腺开口方式相似,而从纵切面和横切面上观察其结构存在一些差异。PAS反应显示象腿蕉泌蜜组织中淀粉粒含量高于其他两个种;芭蕉和象腿蕉的蜜腺腔里有许多纤维状物质存在。3种植物的传粉综合征多样化,花序和花的特征(如花序下垂或直立、苞片的颜色、泌蜜量和泌蜜时间等)和传粉样式之间有密切关系。它们的蜜腺结构和传粉者行为之间没有明显的相关性,但是胶质或水质的花蜜对传粉者的取食方式有一定影响。     

Sago Palm (Metroxylon Sagu, Arecaceae) production in the Eastern Archipelago of Indonesia: Variation in morphological characteristics and pith dry-matter yield

Eleven local varieties of sago palm (Metroxylon sagu Rottb.) in southeast and north Sulawesi and in northern Maluku were studied: one variety with a weak black band on the back of the petiole: three varieties with a brown band on the back of the petiole: seven bandless varieties comprising two spineless, four short spine and one long spine types. Large variation in morphological characteristics and pith dry-matter yield were estimated at 13 to 34% and 55%, respectively. The difference in pith dry-matter yield is mainly attributed to trunk diameter and dry-matter percentage of pith. Trunk diameter was not affected by the length of growth period, which might reflect the palm’s own characteristics, such as genetic background and growth environment. The dry-matter percentage of pith was not related to any characteristics measured. The pith dry-matter yield was highest in the short spine type, followed by the spineless and the long spine types.

---

Produksi Palma Sagu (Metroxylon Sagu, Arecaceae) Di Kepulauan Timur Indonesia: Keragaman Karakteristik Morfologi Dan Hasil Bahan Kering Empulur Batang

Résumé  Dalam survey tersebut dipelajari sebelas varitas sagu lokal (Metroxylon sagu Rottb.) di Sulawesi Tenggara, Sulawesi Utara, dan Maluku Utara: satu varitas dengan pita sedikit hitam pada bagian belakang dari tulang daun: tiga varitas dengan pita coklat pada bagian belakang belakang dari tulang daun: tujuh varitas tanpa pita terdiri dari dua varitas tanpa duri, empat varitas duri pendek dan satu varitas duri panjang. Terdapat adanya keragaman pada karakteristik morfologi dan hasil bahan kering empulur batang yang diperkirakan beriurut-turut berkisar 13 sampai 34% dan 55%. Perbedaan pada hasil bahan kering empulur batang terutama tergantung pada diameter batang dan proporsi kering empulur batang. Diameter batang tidak dipengaruhi oleh panjangnya periode tumbuh; namun nampaknya lebih terkait dengan gambaran karakteristik khusus, seperti latar belakang genetik dan lingkungan tumbuhnya.Persen bobot kering empulur batang tidak ada hubungannya dengan berbagai karakteristik yang diteliti. Hasil bahan kering empulur batang tertinggi adalah pada tipe duri pendek (511kg/batang), diikuti tipe tanpa duri (417kg/batang) dan tipe duri panjang (329kg/batang).

     

Floral structure and development in Nartheciaceae (Dioscoreales), with special reference to ovary position and septal nectaries

We present a comparative study of the floral structure and development of Nartheciaceae, a small dioscorealean family consisting of five genera (Aletris, Lophiola, Metanarthecium, Narthecium, and Nietneria). A noticeable diversity existed in nine floral characters. Analyses of their respective character states in the light of a phylogenetic context revealed that the flowers of Nartheciaceae, whose plesiomorphies occur in Aletris and Metanarthecium, have evolved toward in all or part of Lophiola, Narthecium, and Nietneria: (1) loss of a perianth tube; (2) stamen insertion at the perianth base; (3) congenital carpel fusion; (4) loss of the septal nectaries; (5) unilocular style; (6) unfused lateral carpellary margins in the style; (7) flower with the median outer tepal on the abaxial side; (8) flower with moniliform hairs; and (9) flower with weak monosymmetry. We further found that, as the flowers developed, the ovary shifted its position from inferior to superior. As a whole, their structure changes suggest that the Nartheciaceae flowers have evolved in close association with pollination and seed dispersal. By considering inferior ovaries and the presence of septal nectaries as plesiomorphies of Nartheciaceae, we discussed evolution of the ovary position and septal nectaries in all the monocots.     

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.     

Fine-scale spatial genetic structure and gene flow in Acrocomia aculeata (Arecaceae): Analysis in an overlapping generation

This study aimed to assess the fine-scale spatial genetic structure (SGS) and gene flow among the developmental stages of Acrocomia aculeata (Arecaceae) in a natural population of the Brazilian savannah. The study was conducted in a 4.5 ha area using a population census composed of 72 adult and 144 juvenile plants. Six-hundred embryo samples were analyzed to investigate the gene flow of plant progenies. All individuals were genotyped using seven microsatellite loci. The microsatellite loci generated 10.1 alleles on average. Observed heterozygosity (H_o) was lower than expected heterozygosity (H_e) in all stages of development. The mean H_o and H_e values were 0.496 and 0.688, respectively. The A. aculeata population presented high genetic diversity despite its significant positive fixation index (0.279, p = 0.001). Significant SGS was observed for adults at the 2-m distance class and for juveniles at the 2 and 4-m distance classes. Average pollen flow distance was 105 m. High multilocus outcrossing rate was observed (1.2), indicating that the species is preferentially allogamous with evidence of self-incompatibility mechanisms. The A. aculeata population presents high potential for in situ and ex situ genetic conservation and germplasm collection.     

Embryonic development of the scorpionfly Panorpa emarginata Cheng with special reference to external morphology (Mecoptera: Panorpidae)

The Mecoptera are thought to be one of the most primitive groups in the Holometabola, but their embryology is rarely studied. By means of scanning electron microscopy, we studied the external features of the embryo of the scorpionfly Panorpa emarginata in middle and late development. The embryo remains in the superficial position until hatching. Embryonic development can be divided into 10 stages along with the first‐instar larva. The external features are described from the germ band to the first‐instar larva, with special reference to the components and segmentation of the head, the segmentation of abdomen and the formation of abdominal prolegs. Our results confirm that the head consists of an anterior‐most acron and six trunk segments: the labral, antennal, intercalary, mandibular, maxillary, and labial segments. The labrum is confirmed to derive from the paired appendages. Our observations also provide additional direct evidence that the abdominal prolegs are not serially homologous with the thoracic legs. The presence of the eleventh abdominal segment is clarified. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Floral evolution in the monocot family Nartheciaceae (Dioscoreales): evidence from anatomy and development in Metanarthecium luteo‐viride Maxim.

The placement of Nartheciaceae within Dioscoreales is an unexpected result of molecular phylogenetics. Nartheciaceae generally differs from the rest of Dioscoreales in having less specialized flowers. Studies of this family are important to elucidate the evolutionary history of the order. Using scanning electron microscopy and light microscopy, we describe the details of the flower structure, initiation, and development in Metanarthecium, which is unique amongst Nartheciaceae in possessing both an almost superior ovary and septal nectaries. This is the first member of Dioscoreales for which all stages of organogenesis have been studied. Within Nartheciaceae, the presence/absence of septal nectaries and the position of the ovary are labile. The presence of post‐genital fusion in the gynoecium correlates with the presence of septal nectaries. Septal nectary morphology is complicated in Metanarthecium, which raises the question of whether its floral structure (including superior ovary) is plesiomorphic within Dioscoreales. The septal nectaries of Metanarthecium show homoplastic similarity with those of Allium (Asparagales). The presence/absence of a compitum is probably variable at the infraspecific level in Metanarthecium as a result of alternative possibilities of post‐genital fusion between ventral carpel margins. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 1–18.