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

3f. Senna silvestris (Vellozo) subsp, bifaria var. bifaria Irwin & Barneby, var. nov., intra subspeciem homonymam ut supra descriptam legumine lato (18-30 mm) 40-58-ovulato, seminumque loculis fere omnibus bi- seriatis praestans.—BRAZIL. Goias: Sa. Geral do Parana 3 km s. of Sao Joao da Aliança, 23.111.1973 (fl, fr), W. R. Anderson et al. 7840.— Holotypus, UB; isotypi, F. K, NY, RB, US.

Cassia silvestris sensu Bentham, 1870, p. 125 ("sylvestris"), max. ex parte, exclus. t. 38; 1871, p. 549, max. ex parte., & auct. recentior., non Vellozo, 1825, sens. str.

Potentially arborescent, at anthesis (0.5-) 1.8-6 m, the trunk rarely attaining a girth of 15 cm, except for glabrate sepals villosulous throughout with spreading, incumbent or curly, commonly yellowish or rufous hairs up to 0.1-0.35 mm, the lfts at least thinly villosulous-puberulent above, densely so beneath, there sub- alveolately reticulate, the areoles sharply depressed below level of venules; lvs 1.5-3.5(-4) dm; lfts (4-)5-9(-10) pairs, the larger usually broadly lance- or ovate- oblong obtuse or bluntly acuminulate (5.5-)6- 11 (- 12) x (2.2-)2.4-5.7 cm, at base shallowly cordate to broadly rounded; outer sepals 4-5(-5.5) mm, inner ones up to (7-)7.5-11 mm; petals commonly, perhaps always, red at and just above the claw, thence bright yellow, the longest (15-) 16-21 mm; long anthers 6-8 mm; ovary densely pilosulous along the sutures, glabrous laterally; ovules 40-58; body of pod 10-15.5 x 1.8-3 cm, the coriaceous valves glabrous lustrous, coarsely venulose, the locules aligned in 2 parallel interdigitating rows, alternately in outline simply elliptic-oblong (toward the seminiferous suture) and bottle-shaped (toward the dorsal suture), the septa (2.5-)3-5 mm apart.—Collections: 65.

Cerrado and gallery margins, becoming locally plentiful in disturbed brush- woodland and in hedges, mostly between 400 and 1000 m but ascending to 1200 m on Chapada dos Veadeiros in e.-centr. Goias, widespread and common over the Brazilian Planalto between ±13°S and Tropic of Capricorn, from Sa. do Ron- cador in n.-e. Mato Grosso s.-e. across Goias to n.-centr. Minas Gerais, s. to headwaters of Rio Tiete in s.-e. Sao Paulo; one remote record from 9°S in n. Goias (Guara, within the range of otherwise fully allopatric var. velutina) may perhaps have been introduced along the Belem-Brasilia highway.—Fl. (XI-) XII-IV(V).—Amendoim do campo; avelao.

The var. bifaria, which represents S. silvestris on the Brazilian highlands drained northward by the Araguaia-Tocantins and Sao Francisco rivers and southwestward by the Parana, is most readily distinguished by its coarsely veiny broad many-ovulate pod enclosing two interfingering rows of seed-locules. In Serra do Roncador in northeastern Mato Grosso it is sympatric with var. silvestris but readily distinguished by the pronounced venulation of the leaflets’ lower face. The two varieties again occur close together in south-central Minas Gerais, var. bifaria below 1000 m on the headwaters of Rio das Velhas and var. silvestris at mostly greater elevations on the Atlantic slope. Elsewhere their ranges are mutually exclusive. The var. unifaria, which replaces var. bifaria in central and southwestern Mato Grosso, is entirely similar to var. bifaria at anthesis, but obviously different in the narrower pod and few uniseriate seeds. A similarly narrow but more papery and delicately venulose pod characterizes var. velutina, already distinguishable in flower by the golden-strigulose inner sepals and the puberulent anthers.

The variety varies somewhat in density of pubescence and outline of leaflets, and its pod varies in length and breadth to about the same degree as that of var. silvestris. A curious dwarf form, small-leaved and flowering when only 5 dm tall, was collected (Irwin 23921) with normal var. bifaria (Irwin 23915) between Agua Boa and Jequetai in northern Minas Gerais; its genetic structure would make an interesting study.