Macropsychanthus currently comprises 51 species and is divided into two subgenera, Macropsychanthus and Platylobium, which are distinguished by a combination of morphological traits and supported by molecular data. However, certain species present morphological features typical of subg. Platylobium, despite its phylogenetic placement within subg. Macropsychanthus. During our comprehensive revision of Macropsychanthus in the Neotropics, we discovered a new species, here named Macropsychanthus echidna. Phylogenetic analyses based on nuclear ITS/ETS and plastid trnK/matK markers recovered it within subg. Macropsychanthus. Nevertheless, the species displays traits such as triangular, basifixed stipules; exstipellate leaflets with 7–9 pairs of secondary veins; and slightly obovate pods, all features typically associated with subg. Platylobium. Together with Macropsychanthus huberi, this is the second species assigned to the subgenus. Macropsychanthus that displays a morphology largely aligned with subg. Platylobium, thereby challenging the validity of maintaining the current subgeneric delimitation. The short, oblong hilum of the seed remains the only consistent morphological feature distinguishing subg. Platylobium.