Notes on Geissorhiza (Iridaceae): The Species in Madagascar

Abstract

The two Madagascar species regarded as belonging to the southern African genus Geissorhiza, G. bojeri and G. ambongensis are shown to have characteristics incompatible with this genus. Geissorhiza bojeri accords well with Gladiolus and is transferred here as Gladiolus bojeri (Baker) Goldbl. Geissorhiza ambongensis is not sufficiently well known to allow generic placement at this time but is excluded from Geissorhiza. Geissorhiza is a large genus of southern African Iridaceae subfamily Ixioideae. In the only complete modern treatment of the genus, Foster (1941) recognized 55 species in two subgenera. Subgenus Geissorhiza has 51 'species, all from the Cape Flora Region and surrounding areas, and subgenus Ixiopsis has only four, three of which occur in the Cape Region and the fourth, G. bojeri Baker in Madagascar. The second Madagascar Geissorhiza, G. ambongensis, described in 1939 (Perrier, 1939), was treated by Foster among his doubtful and unknown species. Foster saw no specimens, but commented that from the description, it seemed close to G. bojeri, but distinct. Both species were placed in Geissorhiza in the Flore de Madagascar (Perrier, 1946). I am at present revising Geissorhiza and it has become clear to me during this study that the two Madagascar species do not belong in Geissorhiza at all. THE MADAGASCAR SPECIES OF GEISSORHIZA 1. Geissorhiza bojeri. The earlier of the two Madagascar Geissorhiza species, G. bojeri was described in 1876 by J. G. Baker, based on collections by Bojer and Hilsenberg from the mountains of central Madagascar. Since then the species has been collected repeatedly and is evidently common on the central plateau in grassland and rocky situations. Geissorhiza bojeri is a slender plant, variable in height from 15 to 35 cm, with two linear, equitant basal leaves, and one to three more, smaller, cauline, partly sheathing leaves, the uppermost often bractlike. The small corms have tunics of fine reticulate fibres, the character that Baker used to distinguish subgenus Ixiopsis, of which G. bojeri is the type species. The bracts are herbaceous and quite short; and the yellow flower is small, short tubed, and apparently actinomorphic, with lanceolate tepals. The fruits are unusual in being long and slender and the seeds have an entire, membranous wing. The seeds match exactly those of Gladiolus, and the fruits are similar to fruits of some Gladiolus species, although more slender than any other species known to me. The significant taxonomic characters are the fibrous corm tunics, apparently actinomorphic flower, long capsule, and winged seeds and only one of these, the actinomorphic flower, corresponds with Geissorhiza as it is currently understood.