The genus Dioicodendron includes two or perhaps several species of shrubs and trees found mainly in wet montane forests of Venezuela and to northern Bolivia. This genus has not been well known or documented until recently. It can be recognized by its generally robust woody habit; its unusual interpetiolar stipules, which are usually rounded and reflexed; its many-flowered cymose to paniculiform terminal inflorescences; its small, white to pale green, unisexual flowers borne on dioecious plants; its corollas with four lobes that are generally longer than the tube; and its numerous small, ellipsoid to obovate, papery to woody septicidal capsules with tiny angled to subglobose seeds. These plants were originally included in Chimarrhis provisinally, but were separated from that genus by Steyermark (1963) based on the dioecious breeding biology, 4-merous flowers, glabrous filaments, and distinct stipule form. Bremer & Eriksson (2009) included Dioicodendron together with Chimarrhis in the tribe Dialypetalantheae (correctly cited there under the name Condamineeae); dioecious reproductive biology is rare or perhaps restricted to Dioicodendron within this group. Delprete (1999: pp. 189-190, figs. 82, 83) provided a diagnostic illustration of the characters of the genus, and micrographs of the seeds (p. 41, fig 11A) and pollen (p. 51, fig. 18G-H).

In the protologue, Steyermark (1963) described the corollas of Dioicodendron as 5-lobed, but this is apparently a typographical error because he separated this genus here based on the flowers that are "tetramerous". Steyermark recognized two species, and the range of the genus as only extending to extreme northern Peru. Dioicodendron was revised by Delprete (1999), who recognized one widespread variable species and synonymized several names. Delprete described the corolla lobes in bud as "valvate with contact zone"; these are valvate similarly to other Rubiaceae, and the meaning of this is not entirely clear. Delprete described the stigmas as spreading in the middle parts but remaining coherent or in contact at maturity, but in at least some plants these are spreading maturity. Delprete considered Dioicodendron dioicum to be at significant risk of extinction due to habitat destruction of seasonal forest vegetation in the Andes, but this does not seem to be the case based on our current knowledge of these plants, which includes documentation of a larger range mainly in wet forests. The taxonomy of Dioicodendron here differs from Delprete's work in recognizing more than one species.

Dioicodendron is similar in general vegetative aspect to some plants of Cinchona, which have well dveloped, ascending, rounded stipules, and these genera have been confused in sterile condition. True Chimarrhis can be separated by its bisexual flowers, usually 5-merous flowers, pubescent filaments, and stipules that are characteristically triangular, acute, and tightly convolute in bud. In a molecular systematic study Kainulainen et al. (2010; as Condamineeae) found Dioicodendron to belong to their Tribe Dialypetalantheae, but in basal position with its relationships not entirely clear.

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

• Delprete, P. G. 1999. Rondeletieae (Rubiaceae)—Part I (Rustia, Tresanthera, Condaminea, Picardaea, Pogonopus, Chimarrhis, Dioicodendron, Molopanthera, Dolichodelphys, and Parachimarrhis). Fl. Neotrop. Monogr. 77: 1–226.
• Steyermark, J. A. 1963. Dioicodendron, a new genus of Rubiaceae. Bol. Soc. Venez. Ci. Nat. 15(106): 23–28.
• 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.