Though only 13 genera exist among Dipterocarpoideae, the large genera
Shorea and Hopea are divisible into 14 sections and 4 subsections, respectively,
and Anisoptera is divisible into 2. These sections approach the status of
genera on structural grounds in some cases, but others distinguished on the
same set of character-states are less distinct. This is the reason for their
infrageneric status (4). All these taxa represent natural groups within the
family. Each contains an average of 16 species, though there is much variability
in size, and 5 are monotypic.