Floral anatomy and systematics of Alliaceae with particular reference to Gilliesia, a presumed insect mimic with strongly zygomorphic flowers

The floral structure of Alliaceae is assessed in relation to the systematics of the family, especially the nature of the component parts of the remarkably insect-like flower of Gilliesia graminea. Both presence of solid styles and possession of tenuinucellate ovules represent consistent synapomorphies for Alliaceae and support the separation of Agapanthus and Themidaceae from Alliaceae. Within Alliaceae, absence of septal nectaries (i.e., complete fusion of carpel margins) is a synapomorphy for the sister genera Gilliesia and Gethyum; septal nectaries are present in all other Alliaceae. A gynobasic style and reduced ovule number are probable synapomorphies for the genus Allium. In contrast to most other Alliaceae, in Gethyum and Gilliesia only three (abaxial) stamens (A1, a1, a2) are expressed, as in the apostasioid orchid Neuwiedia, but the perianth of Gethyum is only slightly bilaterally symmetric (zygomorphic), whereas Gilliesia graminea shows bilateral symmetry in all three floral whorls: perianth (suppression of the inner adaxial tepal in most flowers), androecium (suppression of three adaxial stamens), and gynoecium (slight bilateral symmetry, evident in transverse section). The precise relationships of Miersia and Solaria, the other two genera of Alliaceae with bilaterally symmetric flowers, are unknown, but their morphology indicates a close relationship with Gilliesia and Gethyum. Appendages of tepaline origin occur in Gethyum, Gilliesia, and Miersia; their papillate epidermis suggests that they function as osmophores. Their presence in Miersia, which has six stamens, indicates that these novel structures, which develop late in floral ontogeny, evolved independently from stamen suppression in this group. Within Gilliesia graminea, the genetic mechanisms controlling tepal number and shape are apparently unstable, resulting in fluctuating asymmetry. In G. graminea the possession of insect mimicry, presence of osmophores and absence of nectar together indicate a deceitful pollination mechanism similar to that of some Orchidaceae; this would make Gilliesia highly unusual among non-orchid monocots, given that pollination by sexual deceit is normally regarded as exclusive to orchids.     

Evolution of endoapertures in early-divergent eudicots, with particular reference to pollen morphology in Sabiaceae

Endoapertures, the inner openings of compound apertures in pollen grains, are common in eudicots, but occur infrequently in early-divergent eudicot lineages, in which they are restricted to three families: Menispermaceae, Sabiaceae and Buxaceae. Pollen of Sabiaceae was examined using light, scanning and transmission electron microscopy. The endoapertures are large and lalongate, and intine onci are associated with their development. Optimisation of endoapertures onto an existing angiosperm phylogeny indicates that endoapertures have evolved at least three times independently: in Menispermaceae, in Sabiaceae plus Buxaceae (or possibly separately in these two families), and in the core eudicot clade. Sabiaceae are unusual among early-divergent eudicots in that they possess some characters that are more common in core eudicots, including pollen with endoapertures and pentamerous flowers. This indicates either that they are more closely related to core eudicots than is indicated by current molecular evidence, or that these characters are homoplastic. The latter would suggest a high degree of experimentation prior to evolutionary canalisation of some key morphological features in eudicots. The evolution of endoapertures in early-divergent eudicots is probably associated with possession of endexine sculpture (endosculpture) such as endocracks; endoapertures may have been retained in eudicots as a harmomegathic mechanism.     

Floral development and vasculature in Eriocaulon (Eriocaulaceae) provide insights into the evolution of Poales

Background and AimsFloral developmental studies are crucial for understanding the evolution of floral structures and sexual systems in angiosperms. Within the monocot order Poales, both subfamilies of Eriocaulaceae have unisexual flowers bearing unusual nectaries. Few previous studies have investigated floral development in subfamily Eriocauloideae, which includes the large, diverse and widespread genus Eriocaulon. To understand floral variation and the evolution of the androecium, gynoecium and floral nectaries of Eriocaulaceae, we analysed floral development and vasculature in Eriocaulon and compared it with that of subfamily Paepalanthoideae and the related family Xyridaceae in a phylogenetic context.MethodsThirteen species of Eriocaulon were studied. Developmental analysis was carried out using scanning electron microscopy, and vasculature analysis was carried out using light microscopy. Fresh material was also analysed using scanning electron microscopy with a cryo function. Character evolution was reconstructed over well-resolved phylogenies.Key ResultsPerianth reductions can occur due to delayed development that can also result in loss of the vascular bundles of the median sepals. Nectariferous petal glands cease development and remain vestigial in some species. In staminate flowers, the inner stamens can emerge before the outer ones, and carpels are transformed into nectariferous carpellodes. In pistillate flowers, stamens are reduced to staminodes and the gynoecium has dorsal stigmas.ConclusionsFloral morphology is highly diverse in Eriocaulon, as a result of fusion, reduction or loss of perianth parts. The nectariferous carpellodes of staminate flowers originated first in the ancestor of Eriocaulaceae; petal glands and nectariferous branches of pistillate flowers originated independently in Eriocaulaceae through transfer of function. We present a hypothesis of floral evolution for the family, illustrating a shift from bisexuality to unisexuality and the evolution of nectaries in a complex monocot family, which can contribute to future studies on reproductive biology and floral evolution in other groups.     

753. GILLIESIA MONTANA

Gilliesia montana Poepp. & Endl., a bulbous plant from central Chile, is described and illustrated. Suggestions for its successful cultivation are provided.     

Evolution and patterning of the ovule in seed plants

The ovule and its developmental successor, the seed, together represent a highly characteristic feature of seed plants that has strongly enhanced the reproductive and dispersal potential of this diverse group of taxa. Ovules encompass multiple tissues that perform various roles within a highly constrained space, requiring a complex cascade of genes that generate localized cell proliferation and programmed cell death during different developmental stages. Many heritable morphological differences among lineages reflect relative displacement of these tissues, but others, such as the second (outer) integuments of angiosperms and Gnetales, represent novel and apparently profound and independent innovations. Recent studies, mostly on model taxa, have considerably enhanced our understanding of gene expression in the ovule. However, understanding its evolutionary history requires a comparative and phylogenetic approach that is problematic when comparing extant angiosperms not only with phylogenetically distant extant gymnosperms but also with taxa known only from fossils. This paper reviews ovule characters across a phylogenetically broad range of seed plants in a dynamic developmental context. It discusses both well-established and recent theories of ovule and seed evolution and highlights potential gaps in comparative data that will usefully enhance our understanding of evolutionary transitions and developmental mechanisms.     

Morphological evolution in the graminid clade: comparative floral anatomy of the grass relatives Flagellariaceae and Joinvilleaceae

New comparative data are presented on the reproductive morphology and anatomy of two genera closely related to grasses, Flagellaria and Joinvillea, in which the flowers are superficially similar, especially in stamen morphology. This investigation demonstrates some anatomical differences between the two genera. For example, both genera depart from the ‘typical’ condition of tepal vasculature (three‐traced outer tepals and one‐traced inner tepals): in Flagellaria, each tepal receives a single vascular bundle and, in Joinvillea, each tepal is supplied by three vascular bundles. Joinvillea possesses supernumerary carpel bundles, as also found in the related family Ecdeiocoleaceae, but not in Flagellaria or grasses. In the anther, the tapetum degenerates early in Flagellaria, and is relatively persistent in Joinvillea, in which the pollen grains remain closely associated with the tapetum inside the anther locule, indicating a correlation between peripheral pollen (a feature that is common in grasses) and a persistent tapetum. This study highlights the presence of a pollen‐tube transmitting tissue (PTTT) or solid style in the gynoecium of Flagellaria, as also in many Poaceae, but not in Joinvillea or Ecdeiocoleaceae. We speculate that the presence of a PTTT could represent one of the factors that facilitated the subsequent evolution of the intimately connected gynoecia that characterize grasses. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 393–404.     

'Living stones' reveal alternative petal identity programs within the core eudicots

Petals, defined as the showy laminar floral organs in the second floral whorl, have been shown to be under similar genetic control in distantly related core eudicot model organisms. On the basis of these findings, it is commonly assumed that the petal identity program regulated by B-class MADS-box gene homologs is invariant across the core eudicot clade. However, the core eudicots, which comprise >70% of angiosperm species, exhibit numerous instances of petal and sepal loss, transference of petal function between floral whorls, and recurrent petal evolution. In the face of these complex patterns of perianth evolution, the concept of a core eudicot petal identity program has not been tested. We therefore examined the petal identity program in the Caryophyllales, a core eudicot clade in which perianth differentiation into sepals and petals has evolved multiple times. Specifically, we analyzed the expression patterns of B- and C-class MADS-box homologs for evidence of a conserved petal identity program between sepal-derived and stamen-derived petaloid organs in the 'living stone' family Aizoaceae. We found that neither sepal-derived nor stamen-derived petaloid organs exhibit gene expression patterns consistent with the core eudicot petal identity program. B-class gene homologs are not expressed during the development of sepal-derived petals and are not implicated in petal identity in stamen-derived petals, as their transient expression coincides with early expression of the C-class homolog. We therefore provide evidence for petal development that is independent of B-class genes and suggest that different genetic control of petal identity has evolved within this lineage of core eudicots. These findings call for a more comprehensive understanding of perianth variation and its genetic causes within the core eudicots--an endeavor that will have broader implications for the interpretation of perianth evolution across angiosperms.