Methods - Normal practices of herbarium taxonomy have been applied to study all herbarium material available, mainly from AD, B, BRI, C, DNA, E, HBG, K, L, MO, UTB, WAG, and Z.

Key results - Based on an extensive investigation into as many characters as possible, results permitted the identification of new character states, supporting the division of the genus Trianthema into the two subgenera, Trianthema and Papularia. In consequence, species limits can be reliably re-circumscribed, resulting in the recognition of 17 species in the latter subgenus, of which five are described as new here: T. corallicola, T. mozambiquensis, T. pakistanensis, T. ufoensis, and T. vleiensis. Raised to species rank are T. clavata and T. corymbosa, and emended and re-circumscribed are T. crystallina, T. hereroensis, T. parvifolia, T. salsoloides, T. sanguinea, T. sedifolia, T. sheilae, T. transvaalensis, and T. triquetra. Unaltered is the description of T. argentina, for which, however, the critical features are also described and figured in order to permit a sound identification of each species in T. subg. Papularia. Distribution patterns are discussed and possible evolutionary pathways are suggested on a morphological base.