The genus Wellstedia (Boraginaceae: Wellstedioideae) in southern Africa

Abstract

This regional taxonomic revision of the genus  Wellstedia  Balf.f., a member of the family Boraginaceae  s.I. (including Hydrophyllaceae s.str.), is part of a series of publications on the Boraginaceae in southern Africa.  Wellstedia comprises six species, five in Socotra, Somalia and Ethiopia with the remaining one.  W. dinteri Pilg.. occurring in southern Africa.  W dinteri Pilg. subsp. dinteri occurs in Namibia and the Northern Cape, whereas the newly instated subspecies W. dinteri subsp. gracilior (D.R.Hunt) Retief & A.E.van Wyk, based on W. dinteri Pilg. var. gracilior D.R.Hunt, is confined to Namibia only. The disjunct distribution of Wellstedia and numerous other plant and animal taxa between the arid regions of northeastern Africa and southern Africa is usually explained by the postulated periodic existence of an arid corridor between the two regions during the arid phases of the Pleistocene and even earlier.  Wellstedia is treated here in Wellstedioideae, a subfamily of Boraginaceae s.I. but is sometimes placed in a family of its own, Wellstediaceae Pilger. Morphologically Wellstedia displays strong similarity to genera of the Ehretioideae and also to certain members of the Hydrophyllaceae. The genus is characterized by a perennial, dwarf shrub habit, densely hairy leaves. 4-merous flowers, a terminal, bifid style and a 1- or 2-seeded capsule. A key to the two subspecies, diagnostic characters, a distribution map and illustrations of various macro- and micromorphological features are provided.