Summary. A new stem-succulent species of Cynanchum, C. lenewtonii Liede from East Africa, is described. Its affinities within the genus Cynanchum are discussed. In the course of a study on African Asclepiadaceae, the genus Cynanchum has been investigated both in Madagascar and the African mainland. Of the 28 leafless, stem-succulent species of Cynanchum, only one, C. gerrardii (Harvey) Liede, is found both in mainland Africa and Madagascar; the other 27 are endemic to Madagascar. The discovery of a new, leafless species of Cynanchum endemic to East Africa is, therefore, important for a biogeographic understanding of the group as a whole. Cynanchum lenewtonii Liede sp. nov., ramulis semi-succulentis, subtiliter striatis, foliis deminutis. Cynancho gerrardii affine, sed lobis staminalibus coronae longioribus et lobis interstaminalis coronae triangularibus differt. Holotypus: Kenya, Moyale, Gillett 14031, K; isotypus B. Fig. 1. Plants twining, to 2 -5 m high, richly basitonically branched. Shoots perennial, semi-succulent, finely striate, obscurely glaucous, sparsely glabrescent with flexuous, 0 - 3 -0 - 4 mm long trichomes; internodes 25 - 60 cm long, 1 - 5 - 2 - 5 mm diam. Latex white (the note 'clear juice' on Gillett 12964 seems to be an error). Leaves reduced to scales; leaf blades papery, 1 -2 - 1 7 x 06- 0 - 8 mm, ovate, apically acute. Inflorescences always one per node, subsessile, umbelliform, 2-6 flowered, with 2-4 flowers open at the same time. Floral bracts 0-5-0 -7 x 0-6-0-8 mm wide at the base, triangular, glabrous; pedicels 3-4 mm long, glabrous. Floral buds 2-2 5 mm long, 1 -5-2 mm diam., ovoid to cylindrical, with contorted aestivation. Calyx basally fused, abaxially glabrous; free sepal limbs ovate, 0-6-0-7 x 0-4-0-5 mm, apically acute. Corolla rotate to very widely campanulate; corolla lobes fused for ? - Y of their length; 2 5-3-5 x 1-1 -2 mm, abaxially and adaxially greenish-yellow; free parts of corolla lobes recurved, oblong to triangular, apically obtuse to acute. Gynostegial corona white, cyathiform to campanulate, 2-2 -5 mm high, exceeding the gynostegium, partly obscuring it, consisting of staminal (Cs) and interstaminal (Ci) parts fused for M to /4 of total corona length, both staminal and interstaminal parts differentiated, interstaminal parts shorter than staminal parts. Staminal corona parts connate to the filament only, appressed to the back of the stamens, apically inflexed to erect,