Systematics of the Southern African Genus Hexaglottis (Iridaceae- Iridoideae)

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Abstract
Hexaglottis is a genus of six species occurring along the west and south coast of southern Africa, an area of predominantly winter rainfall. It is a member of tribe Irideae subtribe Homeriinae, which is characterized by a cormous rootstock and secondarily bifacial leaves. Hexaglottis is defined largely by an unusual flower structure with shortly clawed subequal tepals and completely divided filiform style arms. This revision includes three new species, H. namaquana, H. riparia, and H. brevituba, and three that were described before 1800. On the basis of chromosome cytology, experimental hybridization, and vegetative morphology. H. nana is excluded from Hexaglottus; it is probably allied to the genus Rheome. The relationships and history of Hexaglottis are discussed, and, following detailed presentation of taxonomically important characters including chromosome cytology. Hexaglottis is analyzed cladistically. Hexaglottis namaquana is suggested to be an isolated and primitive relict and the sister species of the remainder of the genus. The southern African genus Homeria is probably the closest ally and sister group of Hexaglottis. The putative ancestry of these two genera is traced back to a group of species of Moraea section Moraea. Basic chromosome number in Hexaglottis is x = 6, while H. nana has x = 10, a number shared with Rheome and basic for Moraea.

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