Dioecious, erect shrubs or trees, 1-54 m tall. Bark tan to brown within and dark brown to black on the surface but often weathering to gray, peeling in irregular shaped plates to short vertical strips. Leaves opposite-decussate (or mixed with some leaves spirally placed), distinctly narrowed to a decurrent base Juvenile leaves mostly larger than the adult leaves which are otherwise similar twisted at the base so as to appear distichous, in most cases amphistomatic with the abaxial face uppermost on the left side of the shoot and the axial face uppermost on the right side (in a few species the leaves are hypostomatic and without this unique orientation).
There are12 spp. in the three sections through most of the tropical forests of the world, throughout Malesia, where two sections overlap each other. .