Senna obliqua

  • Title

    Senna obliqua

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna obliqua (G.Don) H.S.Irwin & Barneby

  • Description

    23.  Senna obliqua (G. Don) Irwin & Barneby, comb. nov. Chamaefistula obliqua G. Don, Gen. Hist. Diehl. Pl. 2: 451. 1832.—"Native of Peru. Cassia obliqua Ruiz et Pav. in herb. Lamb[ertiano]."—Lectoholotypus, "Cassia obliqua sp. nova. Fl. Per.," BM! = NY Neg. 146; isotypi, †B = F Neg. 1715, F, FI, K, MA (3 sheets in hb. Pavon., mostly labelled "Muna")!—Cassia obliqua Ruiz & Pavon ex Vogel, Syn. Gen. Cass. 40. 1837.

    Cassia obliqua sensu Bentham, 1871, p. 519; Macbride, 1943, p. 175.

    Amply leafy shrubs or treelets up to 6 m, sometimes flowering at 1.5 m, the older branches terete striate, the younger ones angled by ribs descending from the stipules, all these like the petioles minutely, sometimes remotely livid-punctate, appearing glabrous but usually the lower and often both faces of lfts together with inflorescence minutely incurved-puberulent, the foliage moderately bicolored, the membrano-chartaceous lfts dull olivaceous on both faces but paler beneath, the inflorescence of racemes either solitary or 2-3 borne on abbreviated leafless branchlets, either axillary to living lvs and shorter than them or arising from leafless older branchlets.

    Stipules caducous, of developed lvs scarcely known, but probably like those of inhibited axillary buds all linear-setiform, the few seen 4-8 x 0.3-0.5 mm.

    Lvs 1-4.5 dm, diminishing upward along the branchlets; petiole (2.5-)3-12 cm, at middle 1.3-3.5 mm diam, openly shallow-sulcate; rachis (1.5-)2.5-8 cm; gland between proximal pair of lfts sessile or substipitate, ellipsoid or compressed- ovoid-deltoid 2-3.5 mm, glabrous; pulvinules 5-8.5 mm, wrinkled when dry; distal pair of lfts ovate to ovate-elliptic-acuminate (9-) 10-22 x 4-11 cm, ±2-2.5 times as long as wide, at oblique base usually subequilaterally cuneate, the straight or gently incurved midrib either immersed or prominulous above, cariniform beneath, the 8-13 pairs of major camptodrome secondary and all tertiary and reticular venules sharply finely prominulous on both faces; proximal pair of lfts similar, ±2/3 as long, sometimes proportionately broader.

    Peduncles 3-7 cm; racemes 7-25-fld, the axis becoming 1-6 cm; bracts (caducous, little known) apparently lance-ovate submembranous ±2-4 mm; pedicels 2-4 cm; buds subglobose, glabrous or almost so; sepals elliptic-ovate obtuse ±5-6 mm; petals yellow, puberulent dorsally, of subequal size and shape except the vexillar one broader, the longest 16-25 mm; filaments puberulent, those of 4 median stamens 2.5-3 mm, those of 3 abaxial ones 3-4 mm; anthers glabrous but densely papillate, those of 4 median stamens slightly incurved 3.7-4.5 mm, their divaricate beak 0.5-0.9 mm, those of 3 abaxial ones lunate 4.5-5.5 mm, their porrect beak 1-1.2 mm; ovary strigulose; style scarcely dilated, at apex gently incurved and 0.4-0.5 mm diam below the ciliolate stigmatic aperture; ovules 2-seriate, 72-140.

    Pod (not seen fully ripe) stipitate, the short stout stipe 3-5(?-10) mm, the cylindroid, perhaps subquadrangulate, straight body 2-3.5 x ?0.5, perhaps up to 12 x 0.6 cm, abruptly contracted at both ends, the valves slightly constricted around seeds, minutely strigulose; ripe seeds not seen.—Collections: 8.

    Habitat little recorded, sometimes in gallery forest along rivers, to be expected in monte, ±1700-2050 m, local in the inter-Andean valleys of Ecuador (s.-ward from w. Napo) and Peru, where known from the upper Maranon valley in Amazonas (prov. Bongara), the upper rios Huallaga and Pachitea in Huanuco (prov. Pachitea), Pasco (prov. Oxapampa) and Junfn (prov. Tarma).—Fl. VIII, I (the full range unknown), fr. V-VI(-?).

    In the context of its sub-Andean range, this poorly known species can be recognized by its partial cauliflory, small calyx, and papillose anthers. The anthers together with petals about 16-20 (not 7-14) mm long distinguish it from compatriot S. ruiziana. Speculation as to its relationships within ser. Bacillares must wait on discovery of the pod and ripe seeds.