Shrubs or small trees, glabrous or with an indumentum of simple hairs (or also stellate in U. modestum Diels)
Carpels 3–15 (or more), cylindric or obconic, sometimes angular, free, with numerous biseriate ovules; style very short; stigma broadened, bilobed or irregular, rugose or verrucose
Monocarps indehiscent, ellipsoid or cylindric, stipitate, few–many-seeded, somewhat constricted between the seeds, usually succulent
Seeds ± horizontal, without an aril.
Sepals 3, valvate, free, enclosing the petals in bud, at which time the margins form wing-like ridges (see below), often densely ferruginous pubescent
Flowers hermaphrodite or rarely unisexual, axillary, solitary or paired, sometimes borne on the old wood; buds conical; bracteole 1, usually deciduous
Stamens numerous, linear, the cells lateral or extrorse; prolongation of the connective ± capitate; filaments very short
Petals 6, in 2 whorls of 3, usually both valvate but with inner whorl imbricate in one species, free, subequal
Ripe carpels indehiscent, succulent (? or sometimes dry), ellipsoid to cylindric, shortly stipitate, many- to few-seeded.
Sepals 3, valvate, free, enclosing the petals and with the margins folded to form three ± prominent longitudinal wings in bud, often densely brown-pubescent.
Petals 6, in two whorls, both valvate (or the inner one imbricate in U. hexaloboides (R.E.Fr.) R.E.Fr.), expanding and spreading at anthesis, free, subequal (the outer whorl usually slightly longer).
Stamens ?, linear, with thecae extrorse and connective-prolongations ± capitate.
Carpels 3–10 or sometimes more numerous, free, cylindric or obconic, sometimes ± angular, with numerous ovules in two rows; style very short or absent; stigma ± expanded, bilobed or irregular.
Shrubs or trees, not climbing, glabrous or with simple hairs (and also stellate hairs in U. modestum Diels).
Flowers bisexual (rarely unisexual), solitary or paired, axillary, sometimes on the old wood.