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They are trees, shrubs or grasses that have decussate, astipulate leaves. These can be anisophyll with 1 to 4 pairs of basal veins that are more or less parallel to the midvein. Inflorescence is of various forms and is bracteate. The flowers are actinomorphic with a perigynous floral tube. The stamens occur in the same number as that of the petals except in the Mascareignes, but it occurs that the number of stamens is twice that of the petals and that these are arranged in two equal or largely unequal crowns. 

The anthers are split longitudinally during dehiscence or shed their pollen through a single pore. The connective is found below the anthers and is composed of tubercles that are found at the tips where the filaments are attached to the anthers. The ovary is either unilocular with basal placentation or consists of several locules that show axile placentation. Numerous ovules exist. Both the style and the stigma are simple. The fruit is either in the form of a capsule or a berry. The grains are usually very small. 

The genus is composed of some 300 species that are mostly found in the tropical regions. Four species are found in the Mascareignes. 
 They are trees or bushes that generally have smooth barks. The leaves have entire lamina, are found opposite each other, can be petiolate or subsessile with the midvein being very prominent. There are also 2 longitudinally oriented veins that are however not clearly seen, or that are not seen at all. 

Inflorescence is mainly composed of corymbform thyrsi that are formed from umbelliform cymoses. These are found to be attached on stalks found opposite each other or on fasciculate ones. Sometimes solitary flowers do exist as well. Peduncles are either absent or are well developed and are found either solitary or arranged in fascicules at the base of the leaves. Flowers are usually pedicelate with bracts and bracteoles that are usually present. Floral tube is obconic or campanulate. The petals are either blue or white with 8 equal stamens that is composed of axe-shaped anthers. 

Pollen sacs are very small and are longitudinally split. The ovary is unilocular especially in the Mascareignes, shows basal placentation and is found to be completely adhering to the floral tube. The number of ovules varies from 6 to 16. The style is filiform, while the stigma is simple. Fruits are in the form of globular or ellipsoidal berries that still contain remnants form the floral tube. The number of grains varies from 1 to 2 and the embryo is usually folded, while the hypocotyls are long.