The seed coat structure of Didissandra, Ridleyandra, Raphiocarpus (previously all placed in Didissandra) is investigated and discussed with regard to its taxonomic significance. While the species of Didissandra sect. Didissandra display a distinct and fairly uniform testa structure, the two species of sect. Cyrtandroides differ markedly, not only from sect. Didissandra, but also from each other. Ridleyandra has (with one or two exceptions) a very uniform and characteristic testa pattern. This is found both in the Malayan species (with long-tubed flowers; sect. Ridleyandra) and the Bornean ones (with short-tubed or flat-faced flowers; sect. Stilpnothrix) and thus confirms their congenerity. Seed coat structure in Raphiocarpus is heterogeneous, reflecting the obviously artificial nature of the genus.
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