Reduction of Schizostylis (Iridaceae: Ixioideae) in Hesperantha

Abstract

Schizostylis has the floral synapomorphies of the African genus Hesperantha, including style branches dividing at the mnouth of the floral tube, long laxly spreading style branches, and articulated anthers twisted to face inward. The basic chromosome number of Schizostylis, x = 13, is shared in Ixioideae by Hesperantha, Geissorhiza, and a few species of Romulea. Schizostylis then differs from Hesperantha only in its red flowers (occasionally pink) and, more importantly, in its rootstock, a short rhizome. Most species of Hesperantha have white or pink flowers, occasionally yellow or purple, and all have corms with hard woody tunics. We suggest that Schizostylis, which is semi-aquatic and grows along streams in seasonally or permanently waterlogged ground, has acquired a rhizome secondarily by loss of the corm. Neither the rhizome nor the red flower is sufficient grounds to warrant generic separation from Hesperantha. Schizostylis, a monotypic, or at best ditypic, genus of southern African Iridaceae subfamily Ixioideae, extends from the Drakensberg Escarpment of Eastern Cape Province, South Africa, northward through Lesotho, Swaziland, and Mpumalanga Province to eastern Zimbabwe. A plant of habitats that are waterlogged during its spring and summer growing season, Schizostylis grows along streams, wet seeps, and the edges of marshes (Goldblatt, 1991, 1993). Except in its rhizomatous rootstock and red (sometimes pink) flowers, Schizostylis closely resembles the large African genus Hesperantha (ca. 65 spp.) morphologically, and it has all of the critical floral features of that genus. These include green, soft-textured bracts; a well-developed perianth tube; a style dividing at the top of the perianth tube; long, spreading filiform style branches; and anthers twisted to face inward. The last three features are synapomorphies for Hesperantha. Schizostylis also shares a derived basic chromosome number, x = 13, with Hesperantha, Geissorhiza, and some species of Romulea (Goldblatt, 1971). Here we address the hypothesis that Schizostylis is not only immediately related to Hesperantha but is also closely related to species within that genus, thus nested in Hesperantha.