Taxonomic revision of the genus Thereianthus (Iridaceae: Crocoideae)

Abstract

Thereianthus G.J.Lewis is revised, with full descriptions and synonomy, distribution maps, and notes on ecology and taxonomic history. All species are illustrated, and capsule and seed morphology are described for many of the species for the first time. Novel characteristics of the bract, seed, and pollen operculum are used to separate the species into two sections: sect. Brevibracteae Goldblatt & J.C.Manning is distinguished by relatively small bracts, 3–8 mm long and uniformly leathery or soft-textured without thickened veins, seeds with filiform chalazal extension, and pollen grains with 1-banded operculum; and sect. Thereianthus by relatively larger bracts, (7–)8–15 mm long with prominently sclerified veins, seeds without any extension to the chalazal crest, and pollen grains with ± 2-banded operculum. Species in sect. Thereianthus are further segregated into ser. Thereianthus, with heavily ribbed leaves and suberect flowers with arcuate or erect stamens, and ser. Bracteolatus, with plane, inconspicuously veined leaves and ± spreading flowers with declinate stamens. Eleven species are recognized in the genus, all restricted to the southwestern portion of Western Cape. Two new species are described in sect. Thereianthus: T. bulbiferus Goldblatt & J.C.Manning, known from three populations along the West Coast, is distinguished by the unique development of cormels in the lower leaf axil, and by its actinomorphic perianth with white marks at the base of each tepal and ± declinate stamens; and T. elandsmontanus Goldblatt & J.C.Manning, known from a single population in Elandsberg Nature Reserve near Wellington, has distinctive cream-coloured, moderately long-tubed flowers with unusually narrow, linear tepals heavily marked with purple near the base. In adddition, T. lapeyrousioides [now T. minutus] var. elatior G.J.Lewis in sect. Brevibracteae is raised to species status as T. intermedius Goldblatt & J.C.Manning, differing from typical T. minutus by the shorter perianth tube (10–13 vs 20–30 mm), shorter bracts (3–5 vs 6–8 mm), and smaller, ovoid capsules, 4–5 mm long, containing ovoid seeds vs flask-shaped capsules 6–8 mm long and fusiform seeds.