Woody vines, sometimes shrubby; stipules, if present, distinct and persistent; lamina glands, if present, on margin, never on surface. Floriferous bracts eglandular. Sepals leaving outermost petal exposed in enlarging bud; receptacle glabrous on both sides of stamens; stamens 10, all fertile; anthers ± alike; pollen globally symmetrical; gynoecium comprising 3 carpels, all fertile; styles 3. Fruit dry, breaking apart into 3 samaras with the principal wings lateral, with many fine parallel veins, variously reduced in some species; dorsal wing when present distinct from lateral wings at apex and base; nut ± spheroidal; carpophore absent.
The Hiraea clade enjoys only moderate support from molecular evidence—see the phylogenetic tree above, with bootstrap values above the branches, which is from Davis & Anderson (2010 [pdf]). The most important respect in which the five genera are alike is that their samaras all have the lateral wings dominant and the dorsal wing small or absent, but similar fruits are produced in other clades of Malpighiaceae, so we cannot make too much of that similarity. Support for the branches within the clade is weak, suggesting that the relationships among these genera will probably change in future trees. On the basis of their morphology one can say with some confidence that Hiraea, Excentradenia, and Adelphia are rather closely related. Psychopterys, on the other hand, resembles the other genera only in its samaras and marginal leaf glands, and Lophopterys is also quite distinct in most characters. See the discussions under the genera.