Senna scandens

  • Title

    Senna scandens

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna scandens (Ruiz & Pav. ex G.Don) H.S.Irwin & Barneby

  • Description

    24.  Senna scandens (G. Don) Irwin & Barneby, comb. nov. Cassia scandens Ruiz & Pavon ex G. Don, Gen. Hist. Diehl. Pl. 2: 440. 1832.—"Ruiz et Pav[on] in herb. Lamb[ertiano] . . . Native of Guayaquil [Ecuador]."— Holotypus, ticketed by Pavon ‘Cassia scandens sp. nova de Huayaquil,’ BM! = BUNH Neg. 5137.

    Cassia scandens sensu Bentham, 1871, p. 519.

    Treelets 3-4 m probably sarmentose-leaning when crowded, with green obtusangulate and sulcate, amply leafy hornotinous branchlets, pilosulous throughout with fine forwardly accumbent hairs up to ±0.2-0.35 mm, the adult foliage thinly so, the 1ft blades membranous strongly bicolored, sublustrously olivaceous above, pallid dull beneath, often minutely purple-spotted on both faces, the slender pliant racemes axillary to and much surpassed by contemporaneous lvs.

    Stipules erect, narrowly linear-attenuate 5.5-11 x 0.3-0.5 mm, strongly 1-nerved, deciduous before the lf.

    Lvs 18-28 cm; petiole including discolored, when dry shrunken pulvinus 3-5 cm, at middle 1.6-2.1 mm diam, openly shallow-sulcate ventrally; rachis (2-)3.5-5.5 cm, a little longer or shorter than petiole; gland sessile between proximal pair of lfts, plumply or narrowly ovoid 2-2.8 x 1.2-2 mm; pulvinules (3-)4-5 mm; distal pair of lfts obliquely ovate- or obovate-elliptic, obscurely obtusely acuminate 12-17.5 x 5-6.5(-7.5) cm, 2.4-3 times as long as wide, at base shallowly rounded on proximal and cuneate on distal side, the slender, inwardly arcuate midrib with ±10 pairs of camptodrome secondary veins immersed or almost so above, sharply prominulous beneath, a fine tertiary and reticular venulation raised on both faces or merely discolored beneath.

    Racemes laxly ± 15-25-fld, the flexuous, perhaps geotropic axis becoming ±8-15 cm, the several expanded fls standing well below the globose, thinly puberulent buds; bracts narrowly lance-attenuate 3.5-5.5 mm, persistent into anthesis of fl, probably then deciduous; sepals submembranous greenish or livid- tinged and membranous-margined, the outer broadly ovate the inner oblong- ovate, all of subequal length 6.5-7.5 mm; petals yellow, externally puberulent, ±16-17 mm, the 2 abaxial ones slightly narrower and more oblique than the adaxial ones; androecium functionally 7-merous, the staminodes oblanceolate or spatulate 2-2.5 mm, the 7 fertile filaments puberulent, those of 4 median stamens 2-3 mm, of the 3 abaxial ones 1-2.5 mm, the fertile anthers puberulent in the dorso-ventral grooves or glabrate, plumply lance-oblong in profile, including beak 6-8 x 2.3-2.7 mm, the 3 abaxial a trifle shorter than the 4 median, the beaks of all 0.6-0.8 mm, biporose, those of 3 abaxial stamens a trifle more porrect than those of the 4 median; ovary densely silky-strigulose, the short style moderately dilated and ±0.9 mm diam just below the ciliolate stigmatic cavity, this ±0.5 mm diam; ovules (1 count) 136, biseriate.

    Pod and seeds unknown.—Collections: 4.

    Margins of wet lowland forest, sometimes along streams, known only from the first foothills of the Andes in Los Rios and perhaps adjoining Guayas, Ecuador — Fl. Ill—IV(-?).

    Senna scandens was first collected about 200 years ago, probably by Juan Tafalla after the return to Spain of Jose Pavon, who sold to Lambert the specimen described by George Don as Cassia scandens. The species has been collected since, to our knowledge, only in the Andean piedmont east of Babahoyo in Los Rios, and the material, all in young flower, provides insufficient data for firm definition of a species in the critical ser. Bacillares, several members of which are closely similar in general facies. For geographical reasons S. scandens is most likely to be confused with S. oxyphylla var. hartwegii, endemic to lowland Pacific Ecuador in the same latitudes but apparently in a drier belt between the wet foothill forest and the coast. This differs at anthesis in the revolute margin of mature leaflets and especially in the more obviously dimorphic anthers, the beaks of which are differentiated into two markedly different sets, those of three abaxial ones substantially longer and more porrect. The inflorescence of var. hartwegii becomes at full anthesis a terminal panicle of racemes, whereas that of S. scandens consists, at least in the examples before us, of weakly spreading or perhaps pendulous racemes axillary to large contemporaneous leaves and much shorter than them. Senna obliqua, a habitally similar plant of trans-Andean Ecuador and Peru, resembles S. scandens in foliage and lateral inflorescence, but again has strongly dimorphic and in addition pallid-papillate, not smooth brown anthers. For the present, however, no realistic evaluation of S. scandens is possible, knowledge of the pod and seeds being essential for this purpose.