Monographs Details: Senna silvestris subsp. bifaria var. unifaria
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:

3e. Senna silvestris (Vellozo) subsp, bifaria var. unifaria Irwin & Barneby, var. nov., omnibus fere cum var. bifaria congruens sed legumine angusto 10-14 (nec 18-30) mm lato seminibusque minus numerosis ±30-38 (nec 50-58) 1-seriatis diversa.—BOLIVIA: prov. Velasco, VII. 1892 (fr), O. Kuntze s.n.—Holotypus, NY.

Cassia silvestris fma. ferruginea Chodat & Hassler, Bull. Herb. Boiss. II, 4: 693. 1904.—"Paraguay: . . . pr. Bellavista (Apa), Nov., [Hassler] n. 8017a."—Holotypus, G! isotypus, NY!

Cassia silvestris fma. olivacea Chodat & Hassler, Bull. Herb. Boiss. II, 4: 693. 1904.—"Paraguay: . . . pr. Bellavista, Nov., [Hassler] n. 8017."—Holotypus, G! isotypus, NY!

Shrubs up to 6 m, in habit, pubescence, venation of lfts and in flower not different from var. bifaria; lfts 7-8 pairs, the longest ±6-7.5 x 2-3 cm; ovules 30-38; body of pod 10-12.5 x 1.1-1.4 cm, the valves stiffly chartaceous and coarsely venulose, the seminal locules uniseriate, as wide as the cavity and 3-4 mm long.—Collections: 8.

Cerrado, becoming weedy on roadsides, ±300-500 m, locally plentiful in scattered stations, s. and s.-centr. Mato Grosso, Brazil, adjoining s.-e. Bolivia, and extreme e.-centr. Paraguay.—Fl. I—III.

The var. unifaria, which occupies a small peripheral segment of the whole range of S. silvestris contiguous to, but distinct from, those of vars. bifaria, guaranitica and silvestris, is readily distinguished by the combination of dorsally alveolate-reticulate, densely pilosulous leaflets and a relatively narrow but coarsely veined and few-ovulate pod. The foliage is that of var. bifaria, but the pod, except for coarser venulation of its valves, is that of var. guaranitica, perhaps marginally sympatric on Sa. de Amambay along the Brazil-Paraguay border. Dorsally glabrate sepals and coarsely venulose pod combine to distinguish it from the otherwise similar but remotely allopatric var. velutina.