This genus was previously included in Kohautia, however it differs from that in its single, capitate, usually ovoid-shaped stigma and was separated from it by Groeninckx et al. (2010) based on molecular and morphological characters. All (both) of the Madagascar species that were previously included in Kohautia now are classified in Cordylostigma, so at present the genus Kohautia is not documented in Madagascar. Both of the Cordylostigma species currently reported from Madagascar are also widely distributed in Africa.
The corollas of Cordylostigma are salverform, generally red, pink, blue, or purple, 4-lobed, and have quite slender or narrow tubes that are sometimes apparently constricted at the throat. The flowers of Cordylostigma are not distylous. The fruits are capsular, and very similar to those of several other genera including Oldenlandia, Astiella, and Amphistemon.
Cordylostigma is similar to Oldenlandia; however Oldenlandia can be separated by its flowers with 2 linear stigmas. Also generally the species of Cordylostigma have narrow leaves and basically terminal inflorescences that are branched to several orders, while many (though not all) of the species of Oldenlandia have mostly axillary inflorescences that are unbranched or only branched to one order. Cordylostigma is also similar to Pentodon, but Pentodon has short white corollas with 5 lobes.