This genus consists of some 40
to 50 species, with most belonging to tropical regions of Africa and
Madagascar. Some 9 species are found in the Mascarenes.
They are shrubs, more rarely small trees or grasses. Leaves are opposite, or
rarely in 3. Stipules are
interpetiolar, sometimes fused in a sheath, entire or not, often associated
with hairs at the lateral internal base and are persistent.
Flowers are hermaphrodites. Heterostyles
are often small in a branched inflorescence from which each unit is usually a
small capitulum. Some species
have pedicilate flowers. Bracts
Calyx is ovoid or oblong, more or less ribbed, with a small tube and
triangular or linear lobes. The
floral buds are often winged. Corolla
is white, pink or red-violet, sometimes yellow inside.
The ovary is bilocular. The
locules are uniovulated, with ovules basally placed and upright.
Styles with linear stigmatic lobes are characteristics of this genus.
Fruit is fleshy, hemispheric or plan-convex, often having a dorsal
crest indicating the line of dehiscence.
Seed is concave-convex, with a pale testa.