Stenosepala includes one morphologically distinctive species found in the Chocó-Darién region of northwestern South America and southern Central America. This genus is characterized by a shrub or small tree habit; hirsute pubescence on vegetative and reproductive structures; stems with bark that is reddened and/or peeling; persistent triangular stipules; obovate, thin-textured, medium-sized leaves without domatia; terminal dioecious inflorescences of markedly different form; unusual calyx limbs with 4-10 well developed, setaceous or linear lobes; slender, 6-8-merous, white corollas with convolute (contorted) lobes that are acuminate at their tips; and subglobose fleshy fruits with numerous flattened seeds. The specimens frequently dry with a blue color, usually in the fruits but sometimes in the entirely plant. The hirsute pubescence is usually dense and striking. This species has not been reported to be deciduous, but it grows in dry seasonal habitats where the evergreen species characteristically have much thicker-textured leaves. The leaves of Stenosepala generally lack domatia, although a few specimens appear to have a cave-like space under the secondary veins at their abaxial axils, and that space might serve as a domatium. The flower buds are sharply acute at the apex with the tips of the lobes shortly spreading (Persson, 2000a: figs. 1B). The fruits are 2.5-5 cm in diameter.

The staminate inflorescences of Stenosepala are lax, pedunculate, branched cymes with 10-40 flowers borne on well developed pedicels; in contrast, the pistillate inflorescences comprise a single flower with a relatively large ovary portion. The number of calyx lobes is apparently quite variable, between the pistillate and staminate flowers and among staminate plants. The pistillate corollas may be smaller than the staminate, but few pistillate flowers have been documented. The staminate and pistillate corollas are notable in the variation in number of lobes: the staminate corollas are 6-lobed, while the pistillate corollas are 6-8-lobed.

Persson (2000b, 2000c) found Stenosepala placed in the tribe Gardenieae, and within that in the "Alibertia Group", although his analysis did not clearly indicate its relationships within that group. Bremer & Eriksson (2009) then studied the overall systematics of Rubiaceae, and did not find a single, monophyletic group that corresponded to Gardenieae. Mouly et al. subsequently (2014) reviewed Gardenieae in detail along with related groups, and separated the "traditional" Gardenieae into several new, somewhat weakly supported tribes with Stenosepala included in their new Cordiereae; this tribe corresponded generally to the "Alibertia Group" of Persson (2000c). The general morphological characterization of Cordiereae there included a fusiform pistillate stigma and the presence of exotestal thickenings on the seed, which are apparently not found in Stenosepala; Mouly et al. noted that (as with all Rubiaceae groups) several genera have exceptions to the morphological generalizations of their new tribes. Then Persson & Delprete (2017) reviewed the available molecular data for this group and concluded that the support for several of Mouly et al.'s tribes is uncomfortably weak, and they returned to recognizing the "traditional" Gardenieae of Persson (2000b) until this group is better understood.

Stenosepala is not closely similar to any other Neotropical Rubiaceae, but it can be difficult to identify because it is not commonly seen and the staminate and pistillate plants are so very different in flower and fruit. The fruiting plants are generally similar to Genipa, in leaf size and shape and often in a blue drying color; Genipa has caducous stipules, a truncate to shallowly lobed calyx limb, and 1-locular ovaries with parietal placentation. Stenosepala is similar to several species of Randia, but that genus generally has spines and brachyblast growth and also can be recognized by its pollen grains dispersed in tetrads and 1-locular ovaries with parietal placentation.

Authors: C.H. Persson and C.M. Taylor.
The content of this web page was last revised on 4 November 2019.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

• Persson, C. H. 2000. Stenosepala hirsuta, a new genus and species of Gardenieae (Rubiaceae) from Colombia and Panama. Novon 10(4): 403–406.
• Persson, C. H. 2000. Phylogeny of Gardenieae (Rubiaceae) based on chloroplast DNA sequences from the rps16 intron and trnL(UAA)-F(GAA) intergenic spacer. Nordic J. Bot. 20(3): 257–270.
• Persson, C. H. 2000. Phylogeny of the neotropical Alibertia group (Rubiaceae), with emphasis on the genus Alibertia, inferred from ITS and 5S ribosomal DNA sequences. Amer. J. Bot. 87(7): 1018–1028.
• Mouly, A., K. Kainulainen, C. H. Persson, A. P. Davis, K. M. Wong, S. G. Razafimandimbison & B. Bremer. 2014. Phylogenetic structure and clade circumscriptions in the Gardenieae complex (Rubiaceae). Taxon 63(4): 801–818.
• Bremer, B. & T. Eriksson. 2009. Time tree of Rubiaceae: Phylogeny and dating the family, subfamilies, and tribes. Int. J. Pl. Sci. 170(6): 766–793.