Senna leiophylla

  • Title

    Senna leiophylla

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna leiophylla H.S.Irwin & Barneby

  • Description

    67.  Senna leiophylla (Vogel) Irwin & Barneby, comb. nov. Cassia leiophylla Vogel, Syn. Gen. Cass. 25 & Linnaea 11: 672, descr. ampliat. 1837.—"In Brasilia: Sellow leg."—Holotypus, †B, labelled ‘Cach[oeira] de ... 20 Mayo 1823,’ when Sellow was in the valley of Rio Jacui near Cachoeira do Sul, Rio Grande do Sul, = F Neg. 1701; neoholotypus, former isotypus, K! = IPA Neg. 980 = NY Neg. 1462; isotypi, LE, W!—Vogelocassia leiophylla (Vogel) Britton ex Britton & Rose, N. Amer. Fl. 23(4): 259. 1930, solum quoad nom.

    Cassia leiophylla sensu Bentham, 1870, p. 120 & 1871, p. 542, var. extrabrasil. exclus., emend. Brenan, Kew Bull. 21(1): 51. 1967.

    Coarsely leafy, large-fld suffruticose herb at anthesis 7-15 dm, glabrous throughout except for sometimes puberulent pedicels and minutely ciliolate lfts, the smooth, bluntly angled stems branched distally, the foliage subconclorous, the lfts dull olivaceous, the subsessile 1-2-fld racemes at first axillary to developed cauline lvs, distally forming a ± exserted thyrse.

    Stipules erect herbaceous, narrowly linear-attenuate 10-18 x 0.6-1 mm, deciduous before the lf.

    Lvs (below inflorescence, where abruptly diminished) 6-12 cm; petiole including pulvinus 6-16(-22) mm, at middle ± 1-1.6 mm diam, bluntly narrow-margined and openly sulcate ventrally; rachis 1-3 cm, commonly but not always longer than petiole; gland between proximal pair, sessile or almost so, in profile ovate- acuminate ±1.5-2.5 x 0.7-1 mm; lfts of all lvs exactly 2, or of some lvs 3 pairs, strongly accrescent distally, the distal pair varying from obovate to oblanceolate or elliptic, obtuse mucronulate or deltately acute, 3.5-9 x l.6-3.7(-4) cm, 1.7-3.1 times as long as wide, the midrib with (8-)9-14 pairs of camptodrome and often some random intercalary secondary nerves together with connecting tertiary and reticular venulation all coarsely prominulous on both faces, slightly more pronounced beneath.

    Peduncles 1-3 mm; bracts ovate-acuminate 2-3 mm caducous; pedicels 28-48 mm; fl-buds nodding glabrous, plumply obovoid, the sepals separated by emergent petals long before anthesis; sepals well graduated, thinly herbaceous, broadly obovate or suborbicular 13-15 mm, 7-9-nerved from base, the nerves prominent, branched distally and anastomosing; petals of ser. Trigonelloideae but ample and glabrous or nearly so, the longer ones ±26-33 mm; androecium glabrous, the filaments of 4 median stamens 1-1.5 mm, of 3 abaxial ones 5.5-9 mm, the anthers (in two sets) of median stamens 5.5-7.5 mm, their very short divaricate beak biporose, those of 3 abaxial ones 9-12 mm, abruptly narrowed into a beak 1.8-2 mm, the orifice of this as in C. mucronifera but the septum between the pores usually persistent; ovary strigulose; style ±3.5 x 0.5 mm, scarcely dilated distally, narrowed to the stigmatic cavity; ovules ±46.

    Pod when fully formed but unripe resembling that of S. cobanensis at the same stage of maturity, ±8-9 x 0.45-0.5 cm, the seed-locules wider than long and the orientation of the young seeds transverse.—Collections: 4.

    Campo below 300 m, apparently rare and local, known only from scattered stations in s. Paraguay (prov. Guaira), n.-e. Argentina (Misiones, near Posadas, and Corrientes, depto Paso de los Libres) and the Jucui valley in centr. Rio Grande do Sul, Brazil.—Fl. I-V.

    We here adopt without reservation Brenan’s narrow and precise redefinition (1967, l.c.) of Cassia leiophylla, a warm temperate South American senna which had been interpreted by Britton & Rose so as to include the much commoner and more widespread, wholly intertropical S. cobanensis. It resembles the latter in the relatively broad, piano-compressed pod and transverse seeds, but differs in the glabrous, sharply reticulate leaflets. The habitally similar S. mucronifera, vicariant in dispersal between S. cobanensis and S. leiophylla and morphologically intermediate in pubescence and venulation of the leaflets, differs from both in the greatly elongate and narrow pod.