Thymelaeaceae are a medium-sized family composed of 50 genera and ca. 900 species that are mostly confined to Africa, Australia, and Asia. American members of the family account for 12 genera and about 115 species. The family, now widely accepted as a basal lineage of Malvales (Stevens, 2010), is circumscribed here to include three subfamilies: Thymelaeaoideae (ca. 42 genera), Octolepidoideae (8 genera),and a yet to be validly published third subfamily “Tepuianthoideae” (1 genus). In regards to the “Tepuianthoideae”, compelling recent molecular and morphological data suggest that the Northern South American genus Tepuianthus Maguire & Steyermark (previously Tepuianthaceae) is monophyletic and sister to the basal monophyletic subfamily Octolepidoideae (Horn, 2004). Wurdack and Horn (2001) recommended that the genus should be placed in its own subfamily within Thymelaeaceae, a view which is wholeheartedly adopted for this checklist.
Aside from Tepuianthus and the closely related Octolepidoideae, molecular phylogenetic research within the family has mostly focused on the monophyletic subfamily Thymelaeoideae with particular emphasis on South African species of several genera (Lachnaea L., Passerina L., Gnidia L. and relatives) and to a lesser extent, the large, mostly Australian genus, Pimelea Banks ex Gaertn. The earliest studies were based on a couple of chloroplast genes (Van der Bank et al., 2002) that were later combined with ITS data (Rautenbach & Van der Bank, unpubl. data; Beaumont et al., 2009). Support for many of the internal Thymelaeoideae nodes within these phylogenies is only moderate at best. Clearly, additional molecular studies utilizing more markers and much broader sampling are needed to adequately investigate the phylogenetic position and relationships of most genera within the large Thymelaeaoideae subfamily.
Herber’s (2003) morphological classification, which generally follows the conventional tribal classification of Domke (1934), is generally adopted for the World Checklist as it does not seriously conflict with the limited molecular data available for most of the Thymelaeoideae and Octolepidoideae. Within Thymelaeoideae, one Australian genus (Jedda J. R. Clarkson) and several American genera (e.g., Funifera Leandro ex C. A. Mey., Goodallia Benth., Lagetta Juss., Lasiadenia Benth., Linodendron Griseb., Lophostoma (Meisn.) Meisn.) have not yet been sampled in molecular phylogenetic analyses, and the current systematic position of some of these groups remained unresolved in the Herber's (2003) classification.
A good summary of morphological variation in the family (except Tepuianthus) plus generic descriptions and a key to genera is available in Herber (2003). For general discussions of Tepuianthus (treated as Tepuianthaceae) see Kubitzki (2003) and Berry and Rogers (2005).
An electronic generic key including Tepuianthus is being prepared for this website.