Senna nana

  • Title

    Senna nana

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna nana (Benth.) H.S.Irwin & Barneby

  • Description

    89.  Senna nana (Bentham) Irwin & Barneby, comb. nov. Cassia nana Bentham in Martius, Fl. Bras. 15(2): 110. 1870.—"Habitat locis deustis prope Belem et ad rivulum Garapinta in Banda Oriental del Uruguay: St. Hilaire."—Holotypus, St. Hilaire C2/2550bis, P! phototypus s.n., NY!

    Senna nana sensu Burkart, Darwiniana 13: 428, fig. 1. 1964.

    Dwarf, loosely tufted, shortly caulescent perennial herb from black woody roots, at anthesis ±7-10 cm, the petioles, dorsal face and sometimes the corneous margin of the l(-2)-jugate lfts pilosulous with fine whitish spreading hairs 0.4-0.9 mm, the foliage subconcolorous, bright green or glaucescent, the few 1-2-fld racemes axillary to distal lvs and about as long as them.

    Stipules erect, firmly herbaceous linear-lanceolate 2-4.5 x ±0.5 mm, persistent.

    Lvs mostly 3-6 cm; petiole 13-27 mm, at middle 0.5-0.8 mm diam, strongly 3-ribbed dorso-laterally, shallowly sulcate ventrally; gland sessile or almost so at tip of petiole, obovoid or depressed-hemispherical, in profile 0.3-1.3 x 0.5-0.7 mm; lfts mostly 1, rarely 2 pairs, when 2 these separated by a rachis up to 4 mm long, all obliquely obovate or elliptic-obovate obtuse 1.6-3.4 x 1-2 cm, at strongly asymmetric base cordate on proximal and cuneate on distal side, the margin thickened into a conspicuous pallid cordlike rim 0.2-0.3 mm diam, the blades almost veinless above, the midrib and 5-6 pairs of secondary veins pallid and prominent beneath, the latter anastomosing well within the margin, the tertiary venulation faint and erratic.

    Peduncles ±1.5 cm; bracts 3.5 mm; pedicels ±17 mm; sepals thinly herbaceous or the inner ones membranous, oblong-obovate or -elliptic obtuse, the outer ones pilosulous dorsally ±6 mm, the inner 8.5-11 mm; petals yellow glabrous, when dry stramineous faintly brown-veined, in outline oblance-obovate obtuse 13-15 mm, apparently forming a regularly zygomorphic perianth; staminodes linear- oblanceolate ±0.5 mm wide; 4 median stamens: filaments ±2 mm, anthers straight or almost so 3.5 x 1 mm, at apex obliquely rounded-truncate and 1-pored; 2 latero-abaxial stamens: filaments ±4.5 mm, anthers lunate 5 x 1.2 mm, at apex like the shorter ones; abaxial centric stamen sterile, its anther much narrower than that of the juxtaposed antepetalous pair; ovary gray-strigulose; style linear ±2.5 x 0.3 mm, very slightly incurved distally, glabrate, the barbellate stigmatic cavity latero-introrse.

    Pod (scarcely known) turgidly oblong ±3.5 x 1 cm; seeds apparently 2-seriate, turned broadside to membranous septa, areolate.—Collections: 3.

    Habitat scarcely known, to be expected in exposed sunny places in grassland, apparently rare and local below 250 m in n. and w.-centr. Uruguay, s.-w. Misiones, Argentina (dept. Posadas), and to be expected in w. Rio Grande do Sul, Brazil.