Nine species with black filamentous staminodes can be distinguished at present, the differences lying mainly in character states of leaf and calyx base surfaces, and in flower morphology. While flower colours cannot be used to identify a species, the morphology and size of the black filamentous elements appear distinctive for three different groups, which, however, do not agree with groupings suggested by similarities of leaves or calyx surfaces. A key is presented; D. uniondalense is described as a new species; D. boerhavii is re-established as a new name replacing D. insolitum, an illegitimate name. D. bellum, D. edwardsiae, D. hallii, D. lavisii, D. pulchrum, and D. speciosum are described as presently known, and for D. micans Hartmann (2011) is referred to.