Monographs Details: Senna pallida var. brachyrrhachis H.S.Irwin & Barneby
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 2: 455-918.
Description:Variety Description - Shrubs or treelets ±2 m tall, sparsely minutely strigulose distally, the lfts ciliolate and their midrib puberulent beneath, otherwise glabrous, the annotinous branchlets pallid, striped lengthwise, the racemes mostly terminal to brachyblasts, forming a narrow leafy thyrse. Stipules subulate setiform 2.5-5 x 0.15-0.3 mm. Primary lvs 3-6 cm; petioles (1.2-) 1.5-3 cm; rachis 1-2.3 cm, mostly shorter than petiole, the longer interfoliolar segments 2-5.5 mm; leaflets (3-)4-6 pairs, strongly accrescent distally, obovate or oblong-elliptic obtuse or emarginate, the distal pair 9-15 x 4-9 mm, ±2-2.5 times as long as wide, the margins plane, the midrib prominulous beneath, the 4-6 pairs of secondary venules discolored but immersed beneath; gland between proximal pair 2-3 x 0.2-0.5 mm. Peduncles 9-19 mm, 2-3-fld; pedicels 10-13 mm; sepals glabrous dorsally, the broad inner ones 7-8 mm; longer petals 15-17 mm; filaments of long stamens pilosulous 4-5 mm, their anther, including tubular beak, 5.5-7 mm; ovules ±38. Stipe of pod (not seen fully ripe) ±3 mm, the linear body 6.5-7 x 4 mm, the valves plane.-Collections: 7. [Key: "Appendage terminal of lf-stalk subulate or setiform, not modified and dilated into a gland; range of whole species. Continental N. and S. America and Lesser Antilles, s. Windward Is. and Swan Is. in s. Caribbean; anthers nearly always stouter (1.2-)1.3-2 mm diam, abruptly truncate at apex and the tubules there commonly umbonate at the angle opposed to the laterally divaricate, often slightly infra-terminal beak, if whole anther less than 1.25 mm diam and umbo pronounced. Reticulate tertiary venulation imperceptible or almost so on both faces of lfts, these superficially either penninerved or veinless. Lfts or larger primary cauline lvs 2-8(-9) pairs, perceptibly and usually conspicuously accrescent distally, the terminal pair longest; areole of seeds 0.4-0.9 mm in greatest diam. Scattered over s. Mexico and Guatemala. Plants of Pacific Mexico to Chiapas and highland Guatemala. Pod 4-5.5 mm wide; either Sonora-Sinaloa, or Oaxaca-Guatemala. Habitat and dispersal differesnt, in Oaxaca, Chiapas and Guatemala, if below 1000 m the valves of pod raised over each seed into a sharply defined decussate pyamid. Pine-oak forest at 1200-2150 m; valves of ripe pod plane or weakly bullate over each seed. Primary lvs 3-6.5 cm, their rachis 1-3 cm and lfts 3-7 pairs, the longest 9-17(-20) mm; Oaxaca and Chiapas."]

Distribution and Ecology - Pine-oak woodland, 1300-2150 m, locally plentiful in Sa. Madre del Sur in Oaxaca (distr. Sola de Vega) and in the highlands of Chiapas (mun. Tzimol, Totolapa, La Trinitaria, Las Margaritas and Amantenango del Valle).-Fl. VII-I.

Discussion:This montane variety is closely akin to var. longirostrata, but differs in the abbreviated leaf-rachis and smaller, more crowded leaflets, the dimensions given in our diagnosis. Representative material of it was seen by us only when our manuscript was, as we thought, finished, but in time to intercalate the description next following the closely related Guatemalan var. longirostrata.
Distribution:Oaxaca Mexico North America| Chiapas Mexico North America|