Ronabea Aubl. includes three neotropical species of low shrubs found in wet forests and gallery forests from Belize to Amazonian Brazil. Ronabea has opposite leaves; raphides in its tissues; narrowly triangular, persistent, interpetiolar stipules; shortly cymose to subcapitate, few-flowered, axillary inflorescences with bracts; sessile, small, distylous flowers; white salverform corollas with five valvate lobes; bilocular ovaries with the basal ovules solitary in each locule; rather small, purple-black, drupaceous fruits; 2 unilocular pyrenes that are smooth on the adaxial surface and open by a preformed ventral lid; and oily endosperm (Taylor, 2004).

In spite of its small number of species, Ronabea has a rather complicated nomenclatural history as summarized by Taylor (2004), due in large part to their broad ranges and morphological variation. The three species are distinctive, and Ronabea emetica is morphologically rather distinct from the other two species. Smedmark et al. (2014) studied Ronabea latifolia and Ronabea emetica, each represented by one sample, and found them placed on a grade rather than forming a monophyletic group. They suggested that Ronabea is not monophyletic on this basis. These species both include a notably large geographic range with significant morphological and ecological variation, and It seems likely that when they are studied in detail, both of these will be found comprise several distinct species with most of them as-yet undescribed (R. Foster, pers. comm.). In particular Ronabea latifolia varies in leaf size, shape, and pubescence, degree of expansion of the inflorescences, and corolla size. Here this species is circumscribed broadly, pending detailed future studies that will need to include field work. Ronabea emetica is similarly variable across its range, including in fruit color.

Before its association with Psychotria, the identity of Ronabea was unclear and it was applied to species of various genera in various tribes.As the systematics of the Rubiaceae became clearer, Ronabea was long considered closely related to or synonymous with Psychotria L., though a few authors have recognized it as a separate genus of Psychotrieae (e.g., Bremekamp 1934). Ronabea species were anomalous in Psychotria in their oily endosperm and also their combination of axillary inflorescences (i.e., borne in both axils at each node), persistent triangular stipules, and blue-black rather than red fruits. Ronabea is now included in the Lasiantheae, based on both morphological and molecular data (Piesschaert et al., 2000; Smedmark et al., 2014), and Smedmark et al. found it most closely related to the African Trichostachys and the Malagasy Saldinia. 

Author: C.M. Taylor. The content of this web page was last revised on 11 May 2020.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

Neotropics: wet lowland forests and gallery forests, Belize through Central America to the Amazon basin, from Colombia to northern Bolivia, and from the Guianas to eastern Brazil.

• Taylor, C. M. 2004. The neotropical genus Ronabea (Rubiaceae, Lasiantheae). Syst. & Geogr. Pl. 74(1): 35–42.
• Bremekamp, C. E. B. 1934. Notes on the Rubiaceae of Surinam. Recueil Trav. Bot. Néerl. 31: 248–308.
• Piesschaert, F., L. Andersson, S. Jansen, S. Dessein, E. Robbrecht & E. Smets. 2000. Searching for the taxonomic position of the African genus Colletoecema (Rubiaceae): morphology and anatomy compared to an rps12-intron analysis of the Rubioideae. Canad. J. Bot. 78: 288–304.
• Smedmark, J. E. E., S. G. Razafimandimbison, N. Wikström & B. Bremer. 2014. Inferring geographic range evolution of a pantropical tribe in the coffe family (Lasiantheae, Rubiaceae in the face of topological uncertainty. Molec. Phylogen. Evol. 70: 182–194.