Schizocalyx is a genus of perhaps a dozen species of Neotropical trees and shrubs. This genus is characterized by its woody habit; opposite or verticillate, often robust leaves; caducous, calyptrate stipules (i.e., the stipules are fused into a conical cap) that usually split as the leaves emerge; terminal cymose inflorescences with bracts that are often also calyptrate; bisexual, homostylous flowers; a calyx limb of various forms; campanulate to funnelform corollas with 5 lobes that are convolute in bud; and fruits that are small, woody, 2-locular capsules that open loculicidally across the top to release numerous small angled seeds. A detailed morphological description along with a key to the species was presented by Taylor et al. (2011). The calyx limb of some species is calyptrate, similarly to the stipules, or in other species it is open and variously truncate to lobed. In one species, S. bracteosus, the calyx limbs of some flowers bear an enlarged white petaloid lobe, or calycophyll, which is also persistent on the fruits. The corollas are mostly white or in a few species pale green to pink or pale purple, and the flowers are described by many collectors as fragrant. The small fruits are distinctive (though not unique) in dehiscing across the top portion, inside the ring of the calyx limb or its scar; seed dispersal is apparently via a "salt shaker" effect.
The identity and circumscription of Schizocalyx have not been clear until recently, when the morphology of the species was better documented and molecular study (Kainulainen et al. 2010) showed that two genera and several species that were classified in another genus, Bathysa, are in fact closely related to each other. In particular the identity and relationships of Phitopis were unclear for many years, due in part to an inaccurate description of its stipule morphology in the protologue; see the Phitopis page of this Rubiaceae project for more details.
Schizocalyx was monotypic for many years, and distinguished by its petaloid enlarged calyx lobes; such structures are found in various genera in various tribes and subfamilies, and sometimes only in one or a few species of a genus. Schizocalyx bracteosus was included in the similar genus Bathysa by some authors based on its corolla lobes that are apparentl imbricated in bud. However Bathysa, with and without the inclusion of Schizocalyx bracteosus, was heterogeneous morphologically, and both morphology and molecular sequence data (Kainulainen et al. 2010) show that Schizocalyx bracteosus as well as several other species described in Bathysa are better separated. When these species are removed, Bathysa can be characterized well morphologically by its imbricate corolla lobes, though it retains one problematic species from the Amazon basin, which but does not seem to belong to Schizocalyx. The species of Schizocalyx that were included in Bathysa do have convolute corolla lobes, but this arrangement is very hard to discern in many cases because the lobes overlap only very thinly and the corollas of dried specimens often open prematurely and their corolla lobes arrangement is no longer clear. The pollination biology of Schizocalyx cuspidatus was studied by Freitas & Andrich (2013), who found the corolla opens at night and pollination appears to be nocturnal however the stigma is not receptive until morning and the amount of nectar is very small. They proposed that pollination of this species is by stingless bees consuming the pollen.
C.M. Taylor III 2012