Sommera includes 11 species of shrubs and small trees found in wet forests in Mexico, Central America, and western South America. Sommera is characterized by its caducous interpetiolar triangular stipules, opposite petiolate leaaves with lineolate venation, axillary cymose inflorescences with few to numerous flowers, homostylous small to medium-sized 5-merous flowers, tubular white corollas, and fleshy baccate fruits with numerous angled seeds. The pair of stipules in bud are frequently twisted at least weakly. The leaf venation is distinctive with the highest-order veins (or subepidermal fiber bundles) all parallel within the areoles formed by the well developed tertiary and quaternary venation. The calyx limbs are regularly lobed, and usually persistent on the fruits. The corolla lobes have been described as valvate in bud, but in some species these can be considered reduplicate-valvate (e.g., Jacobs & Smith 2595). The ripe fruits are dark red. Many species have dense strigose or silky pubescence. The branching of at least some species is markedly sylleptic. At least two of the species, Sommera parva and Sommera sabiceoides, appear to be sometimes or perhaps usually rheophytic. Sommera donnell-smithii and Sommera sabiceoides are the most commonly collected species.

Sommera has been studied in detail by Lorence (1999, 2012); for a description and details of many of the species, see Lorence's Flora Mesoamericana treatment of this genus (in the upper right of this screen, click on Choose Project and select Flora Mesoamericana). An updated key to the Mesoamerican Sommera species was later presented by Lorence et al. (2015). The two wholly South American species of Sommera were studied by Andersson & Rova (2004).

In a molecular systematic study Kainulainen et al. (2010; as Condamineeae) found Sommera in the Tribe Dialypetalantheae, and related to the other fleshy-fruited genera of this tribe, Pentagonia, Tammsia, and Hippotis. Sommera is indeed similar to Hippotis, which has spathaceous or irregularly few-lobed calyx limbs and flowers that are solitary or in cymes of up to half a dozen with larger corollas. Sommera is also similar to Sabicea, which has areolate higher-order leaf venation, persistent stipules, and a vining habit. Sommera is also similar to Tammsia, with the flowers 5- or often 6-merous, a well developed calyx that is deeply 3-lobed, and larger corollas. Sommera is also similar to Amphidasya, in particular Amphidasya venezuelensis, which however lacks lineolate venation or fiber bundles in the leaves and has dry non-fleshy fruits.

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

• 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.
• Lorence, D. H., C. M. Taylor, C. D. Adams, L. Andersson, W. C. Burger, P. G. Delprete, K. Es, T. McDowell, H. Ochoterena-Booth, C. H. Persson, F. Piesschaert & D. W. Taylor. 2012. Rubiaceae. 4(2): 1–288. In G. Davidse, M. Sousa Sánchez, S. Knapp & F. Chiang Cabrera (eds.) Fl. Mesoamer. Missouri Botanical Garden, St. Louis.
• Lorence, D. H. 1999. A nomenclator of Mexican and Central American Rubiaceae. Monogr. Syst. Bot. Missouri Bot. Gard. 73: 1–177.
• Lorence, D. H., A. C. Dietzsch & D. L. Kelly. 2015. Sommera cusucoana, a new species of Rubiaceae from Honduras. PhytoKeys 57: 1–9.
• Andersson, L. & J. H. E. Rova. 2004. 162. Rubiaceae (Part 4), Tribe 9. Hippotideae. 74: 1–44. In G. W. Harling & L. Andersson (eds.) Fl. Ecuador. University of Göteborg, Göteborg.