Monographs Details: Senna silvestris subsp. bifaria var. velutina
Authors:Howard S. Irwin, Rupert C. Barneby
Authority: Irwin, Howard S. & Barneby, Rupert C. 1982. The American Cassiinae. A synoptical revision of Leguminosae tribe Cassieae subtrib Cassiinae in the New World. Mem. New York Bot. Gard. 35, part 1: 1-454.
Discussion:

3d. Senna silvestris (Vellozo) subsp, bifaria var. velutina Irwin & Barneby, var. nov., a var. bifaria leguminis angustioris 10-12 (nec 18-30) mm lati loculis minus numerosis ±26-30 (nec 40-58) uniseriatis, a var. unifaria leguminis caeterius similis valvulis chartaceis tenuivenulosis, ab am- babus sepalis interioribus ad medium dorsum dense aureo-strigulosis (nec glabris) diversa.—BRAZIL. Maranhao: municipio de Loreto, n. of Fazenda 'Morros,' ±35 km s. of Loreto, 350 m, 2.V.62 (fl, fr), G. & L. Eiten 4490.—Holotypus, NY (2 sheets).

Shrubby or subarborescent, at anthesis (1.5-)2-6 m, with pubescence, venulation of lfts and general aspect of the subsp., the annotinous stems densely velvety-pilosulous; lvs (10-) 12-25 cm; lfts (5-)6-8 pairs, ovate-oblong obtuse- mucronulate from rounded or shallowly cordate base, the longest 5-9.5 x 2-4 cm, 1.6-3 times as long as wide; sepals densely golden-strigulose dorsally, the short outer ones overall, the inner with broad glabrous border, these up to 9-13 mm; petals yellow, the 3 adaxial ones sometimes orange at base, the longest 1.55-2 cm; body of long anthers puberulent in the grooves, 8-11 x 1.4-2 mm, the beak 1-1.4 mm; ovary densely golden-pilose overall; ovules 26-30; body of pod 10-13 x 1-1.2 cm, the chartaceous valves finely venulose (as in var. silvestris), the locules 1-seriate.—Collections: 12.

Cerrado, 150-550 m, locally plentiful in the middle Xingu, middle Tocantins and Parnaiba valleys between 6° and 9°S in s.-e. Para, n. Goias and s. Maranhao and s. along crest of Espigao Mestre in w. Bahia to ±13°S.—Fl. III-VIII.

The range of var. velutina coincides with the floristically critical zone where the shrub-savannas (cerrado, taboleiro) of the Planalto interfinger and intergrade with the Hylaean forest. Three varieties of S. silvestris are known to occur in the Tocantins valley between 5° and 9°S latitude: typical var. silvestris extending south to 8°S; var. bifaria at one detached northernmost outpost at 9°; and var. velutina between them. The var. velutina is morphologically intermediate to the degree that it combines the dense vesture and dorsally alveolate leaflets of var. bifaria with the chartaceous, delicately veined pod of var. silvestris, but it can hardly be passed off as a set of intergradient populations, for the narrow pod, the densely golden-strigulose sepals and pilosulous anthers are found in neither of the possible parent stocks. The variety differs clearly and abruptly from vegetatively similar var. bifaria in the narrow, relatively few-seeded pod and its uniseriate seeds. The remotely allopatric var. unifaria has similarly proportioned pod and ovule-number, but the coriaceous, coarsely veined pod-valves of var. bifaria.