Monographs Details: Cassia acosmifolia var. oropedii H.S.Irwin & Barneby
Authors:Howard S. Irwin, Rupert C. Barneby
Authority: Irwin, Howard S. & Barneby, Rupert C. 1978. Monographic studies in Cassia (Leguminosae, Caesalpinioideae). III. Sections Absus and Grimaldia. Mem. New York Bot. Gard. 30: 1-300.

148b. Cassia acosmifolia Martius ex Bentham var. oropedii Irwin & Barneby, var. nov., a var. acosmifolia caulibus multo iongius herbaceis viridibus setis 0.6-1.5 mm usque hispidis, racemis laxifloris, alabastris ovoideis nec obpyriformibus remote setosis nec villosulis pyramidatim vel racemose ultra flores expansis elevatis, sepalisque latius lanceolatis ovato-ellipticisve abstans. — BRAZIL. Distrito Federal: Rio Contagem, ±35 km n. of Brasilia, 900 m, 8.111.1966, fl, fr, Irwin, Souza, Grear & Reis dos Santos 15725. — Holotypus, UB; isotypi, K, NY, RB, US.

Characters as given in the key. — Collections: 9.

Margins of gallery forest and thickets in cerrado, sometimes in partial shade, 900-1040 m, local on the Planalto of e. centr. Goias, from Pirenopolis n.-e. through Distrito Federal to Serra Geral de Goias (Formosa; Sao Joao de Alliança) and e.-centr. Mato Grosso (Xavantina). — Fl. III-VI, perhaps later.

The first collection of C. acosmifolia var. oropedii, collected by Pohl in 1819 or 1820 near Pirenopolis (Meia Ponte), was noted by Bentham (1870, p. 133) as a form of C. barbata atypical in its small leaflets and setulose stems. As modern collections have filled in to some extent the ranges of dispersal and morphological variability of the Absoideae, Pohl's plant has emerged as characteristic of a cassia endemic to the highlands of southeastern Goias which differs from genuine C. barbata, apparently confined to northeastern Brazil, not only in the size but also in the simpler, more open reticulation of the leaflets and in the more numerous but at the same time fewer-flowered racemes that form a leafy thyrsoid panicle. The epidermis of young branchlets of C. barbata bearing the usually massive and solitary terminal raceme is already by anthesis pallid and exfoliating in ribbons, whereas that of C. oropedii remains green throughout the first season, turning brown but not exfoliating the second year. A much closer relative, unsuspected by Bentham, is the still indifferently understood typical C. acosmifolia, essentially the same in size, texture and venation of the leaflets-and hardly different in inflorescence, except that the raceme axis is more contracted and the unopened buds, inversely pyriform rather than plumply ovoid, are cymosely clustered near the level of the open flowers, not racemosely elevated well beyond them. With these differences are associated, in var. oropedii, a less woody trunk, a much ampler annual increment of stem and branchlets which appear entirely herbaceous within the limits of the standard herbarium specimen, and relatively broad sepals. The ranges of the two varieties appear quite distinct.