Cosmocalyx includes one species, which is a large tree with unusual fruits that is found in southern Mexico and northern Central America. It is characterized by its tall tree habit, medium-sized petiolate leaves, interpetiolar triangular stipules that are straight in bud and quickly deciduous, terminal paniculiform inflorescences with rather numerous flowers and regularly developed small bracts, 4-merous flowers that are apparently homostylous, short calyx limbs with one lobe larger than the others, salveform yellow corollas with the tube 3-4 mm long and the lobes imbricated in bud, much longer than the tube, and reflexed strongly at anthesis, exserted long slender anthers, a single long linear stigma, a bilocular ovary with the ovules solitary in each locule, and indehiscent dry fruits that are slenderly cylindrical and have a large papery calycophyll with a well developed stipe. The calycophyll or semaphyll in the Rubiaceae is an enlarged calyx lobe, which functions variously for pollinator attraction and/or fruit or seed dispersal. In Cosmocalyx the calycophyll of the fruit forms from the largest lobe of the calyx limb, and enlarges markedly as the fruits develop: the calyx lobe at flowering is 1-1.2 mm long and triangular to ligulate, while the fruiting calycophyll has a slender stipe 3-8 mm long and an ovate blade 20-35 x 8-18 mm.

Cosmocalyx is unusual in Rubiaceae in several other of its morphological features also. Dried specimens and wood exposed to air characteristically have a reddish purple tint, similarly to many specimens of Simira. The corolla lobes are much longer than the tube, and apparently strongly recurved at anthesis. The stamens are inserted in the upper part of the tube, and the filaments are flattened and about as wide as the anther. The anthers are dorsifixed close to the base, and sagittate at that base (these were described as basifixed previously but that appears to be inaccurate). The anthers become longitudinally twisted after anthesis. The higher-order leaf venation is very closely regularly reticulated. For a detailed description of the genus and its one species, see the Lorence's treatment in Flora Mesoamericana (in the upper right corner of this current web page, click on "Choose Project" and then on "Mesoamericana").

Cosmocalyx is similar in general to Deppea, including in the reddish purple tinge of the dried specimens; Deppea differs in its generally shrub or small tree habit, convolute corolla lobes, and fruits that are dehiscent capsules without large calycophylls. Cosmocalyx is also similar to Simira, which differs in its markedly twisted stipules, 2-lobed stigmas, and subglobose woody fruits that are dehiscent and contain numerous flattened winged seeds.

Authors: C.M. Taylor & D.H. Lorence.
The content of this web page was last revised on 21 December 2015.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

• Delprete, P. G. 1998. Notes on calycophyllous Rubiaceae, Part III. Systematic position of the monotypic Mexican genus Cosmocalyx and notes on the calycophyll development. Brittonia 50(3): 309–317.