Notes on Euphorbia sect. Denisophorbia (Euphorbiaceae) in Madagascar: description of a new species and a new synonymy

The identity of the poorly known species Euphorbia commersonii Baill. (Euphorbiaceae) is clarified. This species occurring in the Fort-Dauphin region (in the Southeast of Madagascar) is assigned to Euphorbia sect. Denisophorbia (Leandri) Croizat. Formerly considered as a later synonym of Euphorbia thuarsiana Baill., Euphorbia commersonii is reinstated and Euphorbia elliotii Leandri is considered as a later synonym. A lectotype is designated for the latter species. Euphorbia neoelliotii J.-P. Castillon & J.-B. Castillon, belonging to the same section, is described and illustrated. This new species is distinguished from Euphorbia commersonii by its more elongated and much less coriaceous leaves and its incyathescences with short green peduncles bearing a single green cyathium with tiny cyathophylls appressed to the involucre.