This species is frequently confused with D. madagascariensis DC., with which it often grows. Thus one commonly finds herbarium material consisting of a mixture of the two species. Milne-Redhead and Taylor studied the two species growing together near Songea, and d that D. affinis occupied “rather wetter places” than D. madagascariensis and had longer petioles and leaf-blades and the blades were “paler to more flesh-coloured; petioles less red; few and shorter glands on reddish calyx; petals mauve; calyx more or less erect in fruit; leaves not reflexed in age.” D. madagascariensis on the other hand had “leaves pale red with bright red petioles. .. reflexed in age. .. petals pinkish-mauve and calyx spreading in fruit.”  Forms with slender flexuous stems and shorter leaves were described by Oliver in F.T.A. 2: 403 (1871) as D. flexicaulis. However, a whole range of intermediates between D. flexicaulis and D. affinis has since been found and it is no longer possible to keep them apart. Diels in E.P. IV. 112: 82 (1906) describes the seeds of D. flexicaulis as fusiform and those of D. affinis as ovoid, but on examination the seeds were found to be fusiform in the type-specimens of both.