Revision of the African genus Crotonogyne (Euphorbiaceae)

The African genus Crotonogyne was described in 1864 by Müller Argoviensis with one species, C. manniana Müll. Arg. from the island Bioko of Equatorial Guinea. Baillon (1891) described the second species, a rheophyte from Gabon, but placed it in Manniophyton. Pax (1894, 1897, 1899) and Prain (1911, 1912a, 1912b, 1912c) published most of the 23 specific names available (Govaerts et al. 2000). Pax & Hoffmann (1912) classified it in the subfamily Crotonoideae, tribe Chrozophoreae in a group of genera with an irregular 2–3-lobed male calyx. In the same publication they subdivided Crotonogyne into Crotonogyne s. str. with free male petals, counting two species, the type species C. manniana and C. preussii Pax, and a separate genus Neomanniophyton with male petals fused at the base for the remaining 12 species. Because Crotonogyne manniana has in fact fused male petals, Prain (1913) correctly observed that Neomanniophyton is superfluous. For Crotonogyne preussii, the second species of Crotonogyne s. str., he suggested, eventually, a sectional position as an adequate recognition. Pax (1914) however, reduced Neomanniophyton to a subgenus of Crotonogyne and wrongly transferred C. manniana to it. Webster (1994) placed Crotonogyne in the subfamily Acalyphoideae, tribe Aleuritideae, subtribe Crotonogyninae Webster (1975), together with two other African genera Cyrtogone and Manniophyton. Radcliffe-Smith (2001) followed Webster (1994) in his classification of the genus Crotonogyne. The genus has not been revised on an African scale since 1912 when it was treated for the Flora of tropical Africa by Prain (1912c) and in the same year in Das Pflanzenreich by Pax & Hoffmann (1912). Identification of new material collected since proved to be very difficult due to incorrect or incomplete delimitation of the species. A complete revision is therefore undertaken, also as a basis for the treatment of the genus in the Flore du Gabon.