|Goyder, DJ; Liede-Schumann, S: Notes on Cynanchum and Pentarrhinum (Apocynaceae: Asclepiadoideae) in tropical Africa, Kew Bulletin, 63, 463-466 (2008)|
Critical re-examination of the type of Cynanchum clavidens N. E. Br. has resulted in revised synonymy for C. hastifolium K. Schum. and the description of a new subspecies, C. hastifolium subsp. longirostrum Goyder. The geographical and morphological pattern of variation showed by another species pair, C. gerrardii (Harv.) Liede and C. lenewtonii Liede, is comparable to that shown by the two subspecies of C. hastifolium, so C. lenewtonii is reduced to subspecific rank under C. gerrardii. Finally, C. ledermannii Schltr. is transferred to Pentarrhinum E. Mey., and P. abyssinicum Decne. subsp. ijimense Goyder placed in synonymy with it.