1Leaf-rachis with a straight prickle at the junction of each pair of pinnae (originally from tropical South America)
1'Leaf-rachis without a straight prickle at the junction of the pinnae, sometimes unarmed
2Small trees, introduced
2'Armed (or unarmed) herbs, subshrubs or scandent shrubs
3Juvenile branches and leaves covered with stellate hairs (originally from SE Brazil, locally introduced)
3'Juvenile branches and leaves without stellate hairs (originally from S Brazil and NE Argentina)
4Leaves without prickles on petiole and rachis; pinnae 1 or 2 pairs, subdigitate (pan-tropical, of South American origin)
4'Leaves ± prickly on petiole and rachis (except for cultivar M. diplotricha var. inermis); pinnae 4-7 pairs evenly arranged along the rachis (originally from tropical America)