A synopsis of the African genus Whitfieldia (Acanthaceae: Whitfieldieae) and a key to the species

We present a synopsis and an identification key for the 13 species and one subspecies of the African genus Whitfieldia Hook. (Acanthaceae: Acanthoideae: Whitfieldieae). This work is based on the observation and analysis of morphological data from herbarium specimens and photographs of Whitfieldia species, and the study of all the relevant literature on the genus. Whitfieldia latiflos C.B.Clarke ex Stapf from Liberia is reinstated as an accepted species and a full description and illustration are provided. A new subspecies, W. colorata C.B.Clarke ex Stapf subsp. tigrina A.Grall & I.Darbysh., also from Liberia, is described. In addition, W. arnoldiana De Wild. & T.Durand and W. letestui Benoist are treated as synonyms of W. laurentii (Lindau) C.B.Clarke and W. preussii (Lindau) C.B.Clarke respectively for the first time. Eleven names in Whitfieldia are lectotypified. Reference specimens, relevant literature, habitat notes, distribution maps, taxonomic notes and a preliminary assessment of the conservation status and extinction risk are provided for each taxon. Four species are considered to be threatened of which two (W. latiflos and W. rutilans Heine) are assessed as Endangered (EN) while two others (W. purpurata (Benoist) Heine and W. thollonii (Baill.) Benoist) are placed in the Vulnerable (VU) category. In addition, two taxa are assessed as Near Threatened (NT) and one is currently considered to be Data Deficient (DD).