Simira includes about 35 species of small to large trees with multiflowered terminal inflorescences and subglobose capsular fruits. This genus is characterized by elliptic to obovate petiolate leaves; triangular interpetiolar stipules that are convolute-twisted in bud and caducous; broadly pyramidal to rounded, terminal, pedunculate inflorescences; small protandrous 4--5-merous flowers; tubular white to pale green corollas with the lobes imbricated or rarely open in bud; and subglobose loculicidal capsules with numerous flattened winged seeds. The plants characteristically have sap that oxidizes to a bright red or purple-red color when exposed to air, so the sapwood in a bark slash helps identify this genus. The oxidized red coloring is relatively stable and permanent, so it is clearly evident even on relatively old specimens. In some species the entire specimen dries with this reddened color, while in other species this character is evident on dried specimens only in the stem cross-section. The leaves often have domatia. The stipules are sharply acute and tightly twisted in bud. The flowers are generally consistent within a species in the number of calyx and corolla lobes, but some species show regular variation between 4- and 5-lobed. The hypanthium is generally obconic to cylindrical and relatively long, 3-5 mm and usually longer than the calyx limb. As in several related genera, few species have scattered calycophylls (e.g., Simira ecuadorensis). The corolla lobes are imbricated in bud except in a few species (e.g., Simira rhodoclada), where they are apparently open in bud with the top of the corolla plugged by the erect, closely set anthers. The corolla lobes range from relatively quite short to well developed. The corollas characteristically are tubular to funneform at anthesis, but in Simira ecuadorensis the upper part of the corolla flares into a patelliform skirt-like structure. At anthesis the dorsifixed anthers are characteristically exserted on well developed filaments. The stigmas are held in the middle of the flower except in Simira ecuadorensis, where the style is markedly curved so the stigmas are positioned below the anthers. The capsules are often woody and relatively large, to 9 cm in diameter, and usually lenticellate. They usually split into two hemispherical valves, or occasionally into four valves; whether this form is characteristic of individual species is not yet clear. The seeds are generally elliptic to half-moon shaped, and are arranged in a single stack in each locule. Several species have yellowish green or green, open-mouthed corollas that may be pollinated by bats (Simira ecuadorensis, Simira macrocrater). Simira rubescens is the most widespread and commonly collected species.

Simira is widely distributed, but has generally only one or a few species found in any given region. Centers of species diversity are in southeastern Brazil and northern Colombia through Venezuela, but this genus is most commonly collected in the western Amazon basin. This is one of relatively few Rubiaceae genera that is well represented in both wet and dry vegetation. This genus has not seen surveyed as a whole; useful treatments include Steyermark (1972: 299--309), Barbosa & Peixoto (1989), and Lorence et al. (2012: 272--273). The name Sickingia was long used for this genus, but Bremekamp in his studies of the Guianan Rubiaceae confirmed in the 1950's that Simira is an older name for this same group. Species separation in this group has often relied heavily on leaf characters, at least partly due to poor general knowledge of many of the species. The leaves are clearly variable in at least size and some details of form in many species, however. Continuous variation in features such as leaf base shape and pubescence is documented within a few species, which are circumscribed broadly in this regard (e.g., Simira salvadorensis).

The characteristics of Simira are unusual and its relationships were not very clear for some time, then it was found a molecular systematic study by Kainulainen et al. (2010; as Condamineeae) to belong to the Tribe Dialypetalantheae, and to be related to Parachimarrhis. Parachimarrhis can be separated by its inflorescences with numerous rather small capsules, smaller seeds, and tissues that do not oxidize with Simira's characteristic color. Simira is also similar vegetatively to Ferdinandusa, which has cylindrical capsules, and to Chimarrhis, with capsules and angled seeds; both of these other genera lack a reddish purple oxidation color. Simira is also sometimes confused with fruiting plants of Alibertia and Agouticarpa, which have caducous stipules and similar subglobose woody fruits but their stipules are ligulate and held flatly pressed together and their fruits are indehiscent and contain rounded seeds enclosed by fleshy pulp.

This Rubiaceae Project web page treats the species of Mexico, Central America, and northern to western South America; a number of additional species are found in eastern Brazil. The Brazilian species are under study by Margalho, Delprete, & Groppo.

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

• Steyermark, J. A. 1972. Rubiaceae. 23: 227–832. In B. Maguire & Collaborators (eds.) Bot. Guyana Highl.—Part IX. Mem. New York Bot. Gard. New York Botanical Garden Press, Bronx.
• 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.
• Peixoto, A. L. & M. R. V. Barbosa. 1989. As espécies de Simira (Rubiaceae, Rondeletieae) da Amazônia Brasileira. Acta Amazon. 19: 27–46.
• 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.