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Systematics and Phylogenetics of Cyperaceae Subfamily Mapanioideae

Mapania meditensis D.A. Simpson, from Brunei. Photo: D.A. Simpson.

Cyperaceae subfamily Mapanioideae comprises about 150 species in eleven genera and two tribes (Chrysitricheae and Hypolytreae). Understanding the relationships of  Mapanioideae to the rest of Cyperaceae has been problematic, because morphological characters in Cyperaceae are often difficult to interpret in terms of structural homology. In Mapanioideae this is exemplified by the inflorescence, a key source of character data in Cyperaceae generally. There is a particular specialisation of inflorescence structure into units termed spicoids which comprise 2-13 scale-like floral bracts. The two lowest bracts are opposite, keeled and often enclose the upper bracts (when the latter are present). Sometimes they are more or less united. The lower bracts subtend a single stamen, but the upper bracts are usually empty. There is a single gynoecium, which is not subtended by a floral bract. The whole structure is subtended and partially to fully hidden by a larger glume-like bract (spicoid bract). These are further aggregated into spikes. The homology of these units is still unclear. Some workers regard them as a derived type of spikelet (the basic inflorescence unit found in most other Cyperaceae). Others view the spicoid as a flower in which the regular trimerous structure of the flower has been disturbed.

Work on this group has been carried out over the long term and has mainly comprised regional floristic or monographic treatments of the genera. At Kew we have prepared accounts for the Flora of Thailand authored by Simpson and Koyama (1998) and Flora of the Venezeulan Guayana by Simpson (1998). We have also undertaken monographic accounts include a revision of the genus Mapania (Simpson 1992) and subsequent papers describing additional new taxa. More recently our attention has turned to phylogenetic studies of the group, where we have established that Mapanioideae is a strongly supported sister group to the rest of Cyperaceae and that Hypolytreae have a previously unreported pollen type which we have termed ‘Mapania’-type.

Work currently in progress includes a worldwide revision of the genus Hypolytrum and Hypolytrum and Mapania for the Flora of the Guianas. We are starting to look at floral structure in more detail with colleagues in Australia and Belgium. We are also planning detailed molecular phylogenetic studies within Hypolytrum and Mapania, subject to funding.

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