Patterns of Floral Structure and Orientation in Japonolirion , Narthecium, and Tofieldia

Floral evolution requires reassessment in basal monocots, including species formerly assigned to Melanthiaceae, in the light of recent developments in the molecular phylogenetics of monocots. We have investigated flowers of Tofieldia (Tofieldiaceae), Japonolirion (Petrosaviaceae), and Narthecium (Nartheciaceae). We confirm Engler\u27s (1888) hypothesis that orientation of lateral flowers in monocots is dependent on presence and position of additional phyllomes on the pedicel. The type of floral orientation that occurs in Tofieldia is unusual for monocots, since the additional phyllomes are represented by calyculus scales rather than a bracteole, and the outer whorl tepals are initiated alternating with the calyculus scales. In Japonolirion and Narthecium, a bracteole is inserted in an adaxialtransverse or transverse position; either the outer median tepal is adaxial or no single tepal is inserted in the median position. In Tofieldia, the pedicel has a calyculus of an abaxial and two adaxialtransverse phyllomes; the outer median tepal is adaxial. Additional phyllomes on the pedicel are not adaxial, in contrast to adaxial prophylls in the vegetative regions. The presence or absence of a bracteole or calyculus is taxonomically important. Tofieldia pusilla differs from the other species of Tofieldia examined in the absence of a flower-subtending bract, but the calyculus demonstrates some bract-like features in position, structure and development, which can be interpreted as a hybridization of developmental pathways. The abaxial calyculus scale of T. coccinea is delayed in development

The First Genome from the Basal Monocot Family Has Been Misnamed: Taxonomic Identity of Acorus tatarinowii (Acoraceae), a Source of Numerous Chemical Compounds of Pharmaceutical Importance

The basalmost monocot genus Acorus is well-known for its use in traditional oriental medicine. It comprises the groups of A. calamus and A. gramineus. A recent study recognized three species in the latter group, A. gramineus, A. macrospadiceus, and A. tatarinowii. The material currently known as A. tatarinowii has been extensively studied as a source of various chemical compounds and for producing the first published genome of Acorus, which is important for understanding the origin and evolution of monocots. Using the data from morphology, anatomy, and biogeography, we argue that the type material of A. tatarinowii does not match the interpretation of the species name as adopted in the current literature and herbarium collections (to a taxon of the A. gramineus group from Southeast Asia) but rather belongs to the A. calamus group. Moreover, the name A. macrospadiceus also cannot be used because it was invalidly published. Under a narrow species concept, other appropriate species names should be found or proposed for the plants currently named A. tatarinowii and A. macrospadiceus. However, we discourage the use of a narrow species concept in the A. gramineus group as insufficiently justified and suggest recognizing a single polymorphic species, A. gramineus s.l., at least until a comprehensive taxonomic revision of the group is available. Apart from the presentation of our revised taxonomic framework, we update the geographical distributions of Acorus species in Vietnam, Laos, and Thailand

Structure and Development of Flowers and Inflorescences in Burmannia (Burmanniaceae, Dioscoreales)

Species of the genus Burmannia possess distinctive and highly elaborated flowers with prominent floral tubes that often bear large longitudinal wings. Complicated floral structure of Burmannia hampers understanding its floral evolutionary morphology and biology of the genus. In addition, information on structural features believed to be taxonomically important is lacking for some species. Here we provide an investigation of flowers and inflorescences of Burmannia based on a comprehensive sampling that included eight species with various lifestyles (autotrophic, partially mycoheterotrophic and mycoheterotrophic). We describe the diversity of inflorescence architecture in the genus: a basic (most likely, ancestral) inflorescence type is a thyrsoid comprising two cincinni, which is transformed into a botryoid in some species via reduction of the lateral cymes to single flowers. Burmannia oblonga differs from all the other studied species in having an adaxial (vs. transversal) floral prophyll. For the first time, we describe in detail early floral development in Burmannia. We report presence of the inner tepal lobes in B. oblonga, a species with reportedly absent inner tepals; the growth of the inner tepal lobes is arrested after the middle stage of floral development of this species, and therefore they are undetectable in a mature flower. Floral vasculature in Burmannia varies to reflect the variation of the size of the inner tepal lobes; in B. oblonga with the most reduced inner tepals their vascular supply is completely lost. The gynoecium consists of synascidiate, symplicate, and asymplicate zones. The symplicate zone is secondarily trilocular (except for its distal portion in some of the species) without visible traces of postgenital fusion, which prevented earlier researchers to correctly identify the zones within a definitive ovary. The placentas occupy the entire symplicate zone and a short distal portion of the synascidiate zone. Finally, we revealed an unexpected diversity of stamen-style interactions in Burmannia. In all species studied, the stamens are tightly arranged around the common style to occlude the flower entrance. However, in some species the stamens are free from the common style, whereas in the others the stamen connectives are postgenitally fused with the common style, which results in formation of a gynostegium

Morphology of Hydatellaceae, an anomalous aquatic family recently recognized as an early-divergent angiosperm lineage

© 2007 Botanical Society of America, Inc.The family Hydatellaceae was recently reassigned to the early-divergent angiosperm order Nymphaeales rather than the monocot order Poales. This dramatic taxonomic adjustment allows comparison with other early-divergent angiosperms, both extant and extinct. Hydatellaceae possess some monocot-like features that could represent adaptations to an aquatic habit. Ecophysiological parallels can also be drawn from fossil taxa that are known from small achene-like diaspores, as in Hydatellaceae. Reproductive units of Hydatellaceae consist of perianthlike bracts enclosing several pistils and/or stamens. In species with bisexual reproductive units, a single unit resembles an "inside-out" flower, in which stamens are surrounded by carpels that are initiated centrifugally. Furthermore, involucre development in Trithuria submersa, with delayed growth of second whorl bracts, resembles similar delayed development of the second perianth whorl in Cabomba. Several hypotheses on the homologies of reproductive units in Hydatellaceae are explored. Currently, the most plausible interpretation is that each reproductive unit represents an aggregation of reduced unisexual apetalous flowers, which are thus very different from flowers of Nymphaeales. Each pistil in Hydatellaceae is morphologically and developmentally consistent with a solitary ascidiate carpel. However, ascidiate carpel development, consistent with placement in Nymphaeales, is closely similar to pseudomonomerous pistil development as in Poaes.Paula J. Rudall, Dmitry D. Sokoloff, Margarita V. Remizowa, John G. Conran, Jerrold I. Davis, Terry D. Macfarlane and Dennis W. Stevenso

Patterns of Carpel Structure, Development, and Evolution in Monocots

The phenomenon of heterochrony, or shifts in the relative timing of ontogenetic events, is important for understanding many aspects of plant evolution, including applied issues such as crop yield. In this paper, we review heterochronic shifts in the evolution of an important floral organ, the carpel. The carpels, being ovule-bearing organs, facilitate fertilisation, seed, and fruit formation. It is the carpel that provides the key character of flowering plants, angiospermy. In many angiosperms, a carpel has two zones: proximal ascidiate and distal plicate. When carpels are free (apocarpous gynoecium), the plicate zone has a ventral slit where carpel margins meet and fuse during ontogeny; the ascidiate zone is sac-like from inception and has no ventral slit. When carpels are united in a syncarpous gynoecium, a synascidiate zone has as many locules as carpels, whereas a symplicate zone is unilocular, at least early in ontogeny. In ontogeny, either the (syn)ascidiate or (sym)plicate zone is first to initiate. The two developmental patterns are called early and late peltation, respectively. In extreme cases, either the (sym)plicate or (syn)ascidiate zone is completely lacking. Here, we discuss the diversity of carpel structure and development in a well-defined clade of angiosperms, the monocotyledons. We conclude that the common ancestor of monocots had carpels with both zones and late peltation. This result was found irrespective of the use of the plastid or nuclear phylogeny. Early peltation generally correlates with ovules belonging to the (syn)ascidiate zone, whereas late peltation is found mostly in monocots with a fertile (sym)plicate zone

Shoot Development in Members of an Ancient Aquatic Angiosperm Lineage, Ceratophyllaceae: A New Interpretation Facilitates Comparisons with Chloranthaceae

Ceratophyllum is an ancient and phylogenetically isolated angiosperm lineage. Comparisons between Ceratophyllum and other angiosperms are hampered by uncertainty in inferring organ homologies in this genus of specialized aquatics. Interpretation of shoot morphology is especially problematic in Ceratophyllum. Each node has several leaf-like appendages interpreted as verticillate leaves, modified parts of one and the same leaf or parts of two leaves under decussate phyllotaxis. Vegetative branches are axillary, but reproductive units (interpreted as flowers or inflorescences) are commonly viewed as developing from collateral accessory buds. We studied shoot development in Ceratophyllum submersum, C. tanaiticum, and C. demersum using scanning electron microscopy to clarify shoot morphology and branching patterns. Our data support the idea that the phyllotaxis is essentially decussate with appendages of stipular origin resembling leaf blades. We conclude that a leaf axil of Ceratophyllum possesses a complex of two serial buds, the lower one producing a vegetative branch and the upper one developing a reproductive unit. The reproductive unit is congenitally displaced to the subsequent node, a phenomenon known as concaulescence. Either member of the serial bud complex may be absent. There is a theory based on a synthesis of molecular and morphological data that Chloranthaceae are the closest extant relatives of Ceratophyllum. Serial buds and concaulescence are known in Hedyosmum (Chloranthaceae). Our new interpretation facilitates morphological comparisons between Hedyosmum and Ceratophyllum

Inference of Ploidy Level in 19th-Century Historical Herbarium Specimens Reveals the Identity of Five Acorus Species Described by Schott

Heinrich Wilhelm Schott (1794–1865) was one of the pioneering researchers in the taxonomy of the species-rich monocot family Araceae. He described numerous new plant species in various genera, including Acorus, which is currently segregated as a monogeneric family and order occupying a position sister to the rest of the monocots. While describing his new species of Acorus, Schott mostly used characters that are currently considered of low, if any, taxonomic value. His descriptions lack some key characters including, for obvious reasons, chromosome numbers. Therefore, Schott’s species concepts cannot be properly interpreted according to the current understanding of the taxonomic diversity of Acorus, even though his species names must be examined for implementation of the principle of nomenclatural priority. The only way of resolving the taxonomic identity of Schott’s species names is through the identification of type specimens among historical herbarium collections, by inferring taxonomically significant characters that are missing in Schott’s descriptions. On the basis of herbarium collections of the Komarov Botanical Institute, St. Petersburg (LE), we were able to infer ploidy levels of the materials used by Schott to describe Acorus triqueter (diploid, Siberia), A. tatarinowii (tetraploid, China), A. nilaghirensis (tetraploid, India), A. griffithii (tetraploid, Bhutan), and A. commutatus (tetraploid, Bhutan). Leaf anatomy and pollen stainability were used as cytotype markers. All five species belong to the polymorphic Acorus calamus complex that comprises important medicinal plants. Detailed historical and nomenclatural analyses of Schott’s species names and herbarium collections are provided