Calycophyllum includes about 10 species of medium-sized trees or occasionally large (to 45 m tall, Calycophyllum megistocaulum) found in wet to seasonal forests across the Neotropics. Calycophyllum has opposite petiolate leaves, interpetiolar to calyptrate stipules, terminal cymose inflorescences, homostylous protandrous 4--8-merous flowers, medium--sized to somewhat small funnelform white corollas, ca. 2-5 mm long, with thinly imbricate to thinly convolute lobes, exserted anthers and stigmas, bilocular inferior ovaries, and septicidal capsules with numerous winged seeds. Calycophyllum characteristically has distinctive trunks with smooth bark that peeels in thin reddened layers, and Delprete (1996) reported that they lack buttresses and have white wood. Several species of Calycophyllum have showy whitened calycophylls. Delprete (1996) described the genus as having at least one species with 5-merous flowers, and this report has been copied by subsequent authors (e.g., Taylor et al., 2004) but 5-merous flowers have not been confirmed in this genus in this study. Calycophyllum candidissimum in particular is very showy in flower with its large cymse of white corollas, bracts, and calycophylls, and this species forms large showy stands in dry vegetation and is commonly cultivated. This species is common in Nicaragua and is that country's national tree.

Calycophyllum has not been studied as a whole; an outline of the species that are currently recognized is presented here but is mainly based on a summary of the current literature, not a comprehensive review. In a molecular systematic study, Kainulainen et al. (2010; as Condamineeae) found Calycophyllum to belong to the Tribe Dialypetalantheae, and related to Alseis. The flowers of several species of the "Semaphyllanthe" group are poorly known or not yet documented. The population structure in Nicaragua of Calycophyllum candidissimum was studied in detail with genetic data by Dávila-Lara et al. (2017), who found separated populations were still rather well connected genetically and suggested that the wind dispersal of the seeds is effiicient and plays a role.

Andersson (1995) studied Calycophyllum with a morphological cladistic analysis, and found two groups of species that were separated by several characters. Based on this he recognized two genera, Calycophyllum, with three species found in seasonal and wet forest from Mexico to Argentina, and Semaphyllanthe, with six species found in wet forest in South America. Semaphyllanthe was then evaluated morphologically by Delprete (1996) and subsequent authors, who concluded that the characters used to distinguish it were more variable than noted by Andersson, and they did not separate this genus. Kainulainen et al. (2010) first studied this genus with molecular sequence data, and found Calycophyllum sensu stricto separated from the one species of Andersson's Semaphyllanthe that they studied. However this species, Calycophyllum megistocaulum, is not the type species of Semaphyllanthe and was considered "aberrant" and included there only provisionablly by Andersson. Thus, this one species very likely is not be related to the rest of this group, but the status of Semaphyllanthe is not yet clarified. See the genus page for Semaphyllanthe for detailed discussion of its characters and separation. Semaphyllanthe (sensu stricto) is not separated here, because the characters used by Andersson to separate it are variable within other Rubiaceae genera, and a new species that was discovered subsequently combines the characters of both of these groups as noted by Kirkbride (1997). Further study may well show these two genera are distinct, and will be needed to clarify the status of these groups and of Calycophyllum megistocaulum.

Calycophyllum is similar to some species of Chimarrhis, which has interpetiolar stipules that are twisted in bud and protogynous flowers, and to Capirona, which has stipules that split into intrapetiolar segments and much larger pink corollas. Capirona and Calycophyllum megistocaulum are sympatric and both are important timber trees with smooth green trunks, and these species are both sometimes called "capirona" locally. Macrocnemum also has generally smooth, thin-barked trunks, along with interpetiolar stipules that are flat and held erect in bud. Calycophyllum is als similar in to Exostema, which has 5-merous flowers and larger corollas, ca. 8-25 mm long. Calycophyllum is also similar to Warszewiczia, which has interpetiolar sitpules that are twisted in bud, 5-merous protogynous flowers, and small capsules that dehisce mainly through the beak (i.e., disk) portion. Smooth trunks with flaking bark are also found in some species of Guettarda and Stenostomum, with fleshy fruits with a single large bony pyrene.

Author: C.M. Taylor
The content of this web page was last revised on 8 December 2022.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

• Andersson, L. 1995. Tribes and genera of the Cinchoneae complex (Rubiaceae). Ann. Missouri Bot. Gard. 82(3): 409–427.
• Kainulainen, K., C. H. Persson, T. Eriksson & B. Bremer. 2010. Molecular systematics and morphological character evolution of the Condamineeae (Rubiaceae). Amer. J. Bot. 97(12): 1961–1981.
• Delprete, P. G. 1996. Notes on calycophyllous Rubiaceae. Part I. Morphological comparisons of the genera Chimarrhis, Bathysa, and Calycophyllum, with new combinations and a new species, Chimarrhis gentryana. Brittonia 48(1): 35–44.
• Kirkbride, Jr., J. H. 1997. Manipulus Rubiacearum — VI. Brittonia 49(3): 354–379.
• Taylor, C. M., J. A. Steyermark, P. G. Delprete, A. Vincentini, R. Cortés-Ballén, D. C. Zappi, C. H. Persson, C. B. Costa & E. Anunciação. 2004. Rubiaceae. 8: 497–847. In J. A. Steyermark, P. E. Berry & B. K. Holst (eds.) Fl. Venez. Guayana. Missouri Botanical Garden Press, St. Louis.
• Dávila-Lara, A., M. Affenzeller, A. Tribsch, V. Diaz & H.P. Comes. 2017. AFLP diversity and spatial structure of Calycophyllum candidissimum (Rubiaceae), a dominant tree species of Nicaragua’s critically endangered seasonally dry forest. Heredity 119: 275–286.