New Species of the Southern African Genus Geissorhiza (Iridaceae: Ixioideae)

Abstract

Three new species are recognized in the southern African Geissorhiza, a genus now including 84 species. Geissorhiza silenoides and G. rupicola are members of subgenus Geissorhiza and occur in the Ceres District of the southwestern Cape, South Africa. Both have pale pink flowers with unusually long perianth tubes for the genus. Geissorhiza silenoides is additionally distinguished by having unequal stamens, each filament being of a different length, scabrid-puberulent stems, and leaves with heavily thickened margins and midribs. Geissorhiza rupicola has unusual soft-textured corm tunics and, like G. silenoides, has leaves with strongly thickened margins and midribs. The third new species, G. uliginosa, is restricted to the Swartberg Mountains of the southern Cape and grows on wet cliffs and under waterfalls. It stands out in the genus in having the flowers solitary on the stems, and very soft-textured corm tunics that rapidly decay, sometimes leaving the corms apparently without tunics. All three new species occur in the southern and southwestern part of southern Africa, a region known for the richness and diversity of its flora, particularly of geophytes. More than half of the estimated 1750-1800 species of the petaloid monocot family, Iridaceae, occur in southern Africa (Goldblatt, 1994). The region is well known botanically, yet despite over 250 years of botanical exploration, novelties continue to be discovered there. Although the family is a numerically significant element of the flora of a large part of southern Africa, Iridaceae are most diverse in the southern and western coastal belt and adjacent mountains of the subcontinent, a region of mediterranean-type climate with winter rainfall and summer drought. Three new species of Geissorhiza, a genus virtually restricted to the winter rainfall zone of southern Africa, are described here. Some 81 species were admitted to the genus when it was last revised (Goldblatt, 1985), and the new species described here thus bring the total to 84. Geissorhiza is a member of Iridaceae subfamily Ixioideae, the largest of the four subfamilies currently recognized in Iridaceae (Goldblatt, 1990, 1991). It is one of the largest genera of the subfamily and one of the larger genera in the southern African flora. One of the new species, G. uliginosa, belongs in subgenus Weihea, which is characterized by concentric corm tunics, and G. silenoides and G. rupicola are members of subgenus Geissorhiza, species of which have the characteristic imbricate corm tunics that inspired the generic name, a Greek word meaning tiled root. 1. Geissorhiza silenoides Goldblatt & J. C. Manning, sp. nov. TYPE: South Africa. Western Cape: Ceres District, lower slopes of Gydo Pass, 20 Sep. 1993, Goldblatt & Manning 9739 (holotype, NBG; isotypes, K, MO, PRE, WAG). Figure 1A. Plantae 20-30 cm altae, cormo 5-7 mm diametro tunicis duris imbricatis, foiis li nearibus 1.2-1.5 mm latis marginibus costisque incrassatis, spica 4-7 florum, floribus pallide roseis, tubo perianthii cylindrico 15-17 mm longis, tepalis subaequalibus 12.5-14 x 6-7 mm, filamentis inaequalibus 4, 7 et 9 mm longis, antheris ca. 4.5 mm longis, stylo eccentrico. Plants 20-30 cm high. Cormn + ovoid, 5-7 mm diam., flattened slightly below on one side, the tunics woody, blackish, imbricate, the layers breaking below into triangular points. Cataphylls membranous, the upper light purple above the ground. Leaves 4, the lower 2 basal and longest, reaching to at least the middle of the stem, sometimes to the base of the spike, straight and erect or trailing, the blades linear, 1.2-1.5 mm wide, oval in section with 2 narrow grooves on each surface, the midrib much thickened, the margins raised and arched over the surface, the upper leaves cauline, sheathing for at least half their length, the blades like the basal, the uppermost sometimes only 9-12 mm long and enNovoN 5: 156-161. 1995. This content downloaded from 157.55.39.78 on Sun, 19 Jun 2016 06:24:39 UTC All use subject to http://about.jstor.org/terms Volume 5, Number 2 Goldblatt & Manning 157 1995 Geissorhiza from Southern Africa