CHAMAECRISTA [Breyne] Moench
Chamaecrista [Breyne] Moench, Meth. pl. hort. bot. Marburg. 272. 1794.—Generitypus infra sub sect. Chamaecrista indicatur.
Cassia sect. Lasiorhegma Vogel, Syn. Gen. Cass. 8. 1837, nom. illegit. (incorporating 3 prior names of same rank). C. subgen. Lasiorhegma Vogel ex Bentham in Martius, Fl. Bras. 15(2): 129. 1870.
Cassia subgen. Absus (DeCandolle) Symon, Trans. Roy. Soc. S. Australia 90: 77. 1966.
Chamaecrista sensu Greene, Pittonia 3: 238-243. 1897; Britton, Bull. Torr. Club 44: 3-12 & Pennell in op. cit. pp. 339-362; Britton & Rose, N. Amer. Fl. 23(5): 270-299. 1930; Britton & Killip, Ann. N.Y. Acad. Sci. 35: 182-187. 1936; Pittier, Cat. Fl. Venezol. 1: 373-375. 1945, these, however, defined to accommodate only sects. Chamaecrista, Caliciopsis and Xerocalyx; sensu ampliat. Irwin & Barneby, Brittonia 28(1): 28-36. 1976; in Polhill & Raven, 1981, p. 106.
Cassia subgen. Lasiorhegma sensu Irwin & Barneby, Mem. N.Y. Bot. Gard. 30: 2-3. 1977.
General characters of subtrib. Cassiinae, with these particular ones: pedicels 2-bracteolate near or above middle; pod elastically dehiscent, the valves coiling; androecium (erratically) actinomorphic, the 2 cycles of stamens often of different lengths but not bilaterally zygomorphic, the thecae of the anthers ciliolate along the lateral sutures; extrafloral nectaries (Fig. 36), when present, dish- or cupshaped, rarely flat, secreting nectar from a concave (flat) surface; seed-funicle deltately dilated; seed-coat either smooth or pitted, exareolate.—Trees, shrubs, herbs, these perennial or monocarpic; roots bearing bacterial nodules; phyllotaxy spiral or distichous; inflorescence of 1-many-fld racemes, these mostly axillary from hornotinous stems, sometimes cauliflorous, sometimes appearing supra-axillary when peduncle adnate to stem; petals yellow, sometimes red-spotted near claw or suffused with orange-red, nearly always highly heteromorphic, the 2 abaxial ones (sometimes by resupination appearing adaxial) variously oblique and dissimilar between themselves, the larger one often shielding the androecium or interposed between it and the obliquely divergent (enantiostylous) pistil, the vexillar petal commonly interior in praefloration but sometimes exterior on one or both sides; androecium functionally (2-)5-10-merous, the basiflxed anthers longer than their filament, either iso- or heteromorphic, each theca apically dehiscent by a pore or short slit; pod piano-compressed, very rarely winged along the sutures, the valves papery, leathery or subligneous; 2n = 14, 16.—A genus of 6 sections and ±265 species, all sections and 239 species native to the Americas, represented in the Old World by the circumtropical monotypic sect. Absus and by numerous species of sect. Chamaecrista.
The syndrome of bracteolate pedicels, radial or irregular but never bilateral symmetry of the androecium, basiflxed anthers ciliolate along the permanently closed lateral sutures, elastically dehiscent pod and dilated seed-funicle present in every Chamaecrista known to us establishes the genus on an impregnable morphological foundation. Bacterial root-nodules (Corby, 1974) and concave extrafloral nectaries (on leaf-stalk or raceme-axis), when present, are further characteristic, for they occur in no other Cassiinae. The checkered history of the genus and its modem interpretation as equivalent to Bentham’s Cassia subgen. Lasiorhegma have recently been examined in detail (Irwin & Barneby, 1976), and a summary redefinition of it has appeared in our synopsis of the subtribe Cassiinae (Irwin & Barneby in Polhill & Raven, 1981).
Chamaecrista comprises six sectional groups of very unequal size, lately defined as sections of Cassia subgen. Lasiorhegma in the introduction to our monograph of sects. Absus and Grimaldia (Irwin & Barneby, 1977, pp. 2-3). The present synopsis, while comprehensive, deals with each section in varying depth of detail, as seemed appropriate in relation to previously published studies:
Sect. (A) Apoucouita was revised by Irwin & Rogers in 1967 and again, in light of new material, by Irwin & Barneby in 1977; a bare outline, accompanied by a key for identification, and a synoptical list of species are here presented.
Sect. (B) Absus and sect. (C) Grimaldia were revised by Irwin & Barneby in 1977, as sections of Cassia. A census of subsections, series, species and varieties, transferred as necessary to genus Chamaecrista, appears sufficient in this place.
Sect. (D) Chamaecrista (51 spp.) and (E) Caliciopsis (2 spp.) are subjected to detailed analysis and redefinition. Full descriptions, keys to the taxa and a list of numbered Exsiccatae are provided.
Sect. (F) Xerocalyx, subject of the senior author’s doctoral dissertation (Irwin, 1964, the seminal paper in the series concluded herewith), has required extensive elaboration in order to accommodate materials collected on the Brazilian Planalto in recent years. New perspectives gained in fieldwork have imposed a radically revised taxonomy. New keys and descriptions for all taxa are given.