The Acanthaceae comprise more than 4 000 species in some 275 currently recognized genera distributed worldwide. Most taxa occur in the tropics and subtropics with major centers of diversity and richness in Indo-Malesia, Africa (including Madagascar), South America, and Mexico-Central America. Plants occur in most tropical habitats except those at very high elevations (i.e., above 3 000 meters). About 12 genera, including the two largest, Justicia and Ruellia, are pantropical. More than 350 species in 40 genera, representing each of the four traditionally recognized subfamilies (Acanthoideae, Mendoncioideae, Nelsonioideae, and Thunbergioideae) occur in Mexico. Twenty-nine genera and 131 species of Acanthaceae are here included as native or naturalized in Chiapas. The following species are known only from cultivated plants in Chiapas: Acanthus mollis L., Justicia brandegeana Wassh. & L.B. Sm., J. carnea Lindl., and Pachystachys lutea Nees.
The following treatment is conservative, perhaps excessively so at times, in recognition of taxa. In cases where seemingly disparate specimens are included in a single species, a rationale is provided or referenced. Pollen characters are utilized in the key to genera and are sometimes included in the descriptions. In no case is a pollen character the sole basis for distinguishing genera in the key. These micro-characters are provided because classification of the Acanthaceae has been based in large part on differences in pollen. Format of this treatment basically follows that of previous parts in the series.