Senna quinquangulata

Title

Senna quinquangulata

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Senna quinquangulata (Rich.) H.S.Irwin & Barneby

Description

26.  Senna quinquangulata (L. C. Richard) Irwin & Barneby, comb. nov. Cassia quinquangulata L. C. Richard, Actes Soc. Hist. Nat. Paris 1: 108. 1792.—Typus infra sub var. quinquangulata indicatur.

Shrubs, weak bushy treelets and sarmentose bush-ropes mostly (1-) 1.5-7, occasionally clambering into the forest canopy up to 25 m, the rope becoming 1-5 cm diam but the stems mostly much more slender, the annotinous branchlets either angulate or terete striate, variably puberulent, strigulose or pilosulous with fine incumbent, less often appressed or erect (with few subretrorse) hairs up to 0. l-0.4(-0.6) mm, the axes of inflorescence and calyx nearly always gray-puberulent, rarely velutinously pilosulous, the chartaceous lfts strongly bicolored, above lustrously dark- or brownish-olivaceous and either glabrous, puberulent along midrib or finely puberulent (pilosulous) overall, the inflorescence either simply narrowly thyrsiform or more broadly thyrsiform-paniculate, the lower racemes or flowering branchlets mostly leafy-braceteate, the lvs abruptly diminished upward, the upper racemes naked or subtended by vestigial lf-stalks.

Stipules falcately linear-oblanceolate acute or acuminate (3-)4-10 x 0.5-2.5 mm, the blades green or yellow-green, when over 1 mm wide distinctly venulose, caducous and often absent from mature flowering and from almost all fruiting specimens.

Lvs below inflorescence (8-)10-22(-27) cm; petiole including strongly differentiated, discolored but little swollen, finally wrinkled pulvinus (1.8-)2.2-5.5(-6.5) cm, at middle 0.8-2 mm diam, the wings defining the open shallow ventral sulcus narrow thick, scarcely dilated upward under the pulvinules; rachis (9-) 12-32(-40) mm, shorter than petiole; glands (caution: often gnawed) 1 between each pair, arising between or the lower from just above the pulvinules, lanceolate or ellipsoid 0.5-1.5(-l.8) mm diam, either sessile (when tongue- or horn-like) or stipitate (when lance- or claviform), straight or forwardly incurved, in profile (2-)3-6(-7) mm tall, or the proximal one rarely only 1.5-2 mm; pulvinules subcylindric wrinkled (2.5-)3-7 mm, obscurely carinate on anterior side by decurrent lft-blade; lfts of distal pair obliquely elliptic-, ovate-, broadly lance-elliptic- or rarely obovate- acuminate, the acumen varying from short obtuse mucronulate to attenuate acute, the whole blade (5-)6-16 x (2.5-)3-7.5(-8) cm, ±1.5-3 times as long as wide, at base on proximal side broadly cuneate to subcordate, on distal one commonly cuneate, the margins revolute and sometimes also undulate, the gently incurved midrib with (7-)8-13(-14) pairs of major camptodrome (and often some intercalary) secondary veins finely low-prominulous above, more distinctly raised beneath, the tertiary and reticular venulation likewise prominulous on both faces but often more pronounced above than beneath.

Peduncles with raceme-axis (1-) 1.5-8(-10.5) cm; racemes (5-)8-21(-26)-fld; bracts obovate- to elliptic-oblanceolate or lanceolate 1.5-8 x 1-1.8 mm (rarely -3 mm wide but then <5 mm long), incurved over young buds before elongation of pedicel, either early caducous or persisting into anthesis; pedicels at and after anthesis (10-) 12-32 mm; buds globose but the sepals separated before true anthesis by the expansion of petals and androecium; sepals firm subherbaceous, usually densely, often subvelutinously gray-strigulose externally and puberulent within (rarely glabrate), not much graduated, all convexly ovate, oblong-ovate or suborbicular, always obtuse, the longest (4-)4.5-6.5(-7.5), very exceptionally -9 mm, externally nerveless or faintly 3-nerved; petals firm, biscuit- or darker orange-yellow, pubescent externally and at least near base also within, subhomomorphic except the adaxial one sometimes broader, oblong-obovate or oblanceolate beyond the short claw, (9-) 10-15(-17) mm, heavily 3-veined from claw, the veins externally prominent; androecium functionally 7-merous, the filaments puberulent, those of 4 median stamens 0.8-1.8(-2.5) mm, those of 3 abaxial ones (1.5-)2-3.5(-5) mm; anthers glabrous or more commonly either puberulent along the grooves or minutely pilosulous overall, those of 4 median stamens (4-)4.5-9 mm, truncate, with very short 2-porose beak standing at right-angles to the little- incurved body, those of 3 abaxial ones shorter, 3-5.5 mm, with beak hardly longer (-0.9 mm) but slightly more porrect; ovary densely silky-pilosulous or -strigulose, at anthesis incurved over androecium, the more thinly pubescent or glabrate style 2-4 mm, abruptly swollen at apex into a cobra-like head 0.9-2.8(-3) mm diam, the oblique cup-shaped stigmatic cavity 0.6-1.8 mm diam; ovules (112-) 122-196(-220).

Pod pendulous short-stipitate, the stipe 2-4 mm, the narrowly subcylindric nearly straight body 11-33.5 x 0.9-2 cm, the firm, coarsely transverse-venulose valves turning brown or fawn-color, dehiscent along ventral suture to expose the seeds clothed in fetid black pulp; seeds (not well known) biseriate, turned broadside to the septa, broadly oblong or oblong-obovoid compressed, the testa smooth lustrous brown, sometimes broadly but faintly areolate.

Senna quinquangulata is the commonest and most frequently collected of that group of Bacillares collectively characterized by lustrous, marginally revolute leaflets, a gland between each (rarely between only the proximal) pair of leaflets, a thyrsoid-paniculate inflorescence arranged around a straight primary axis, and a pod lacking thickened margins to the sutures. In the lower Amazon valley, interior Guayana, the middle Orinoco basin and parts of northern Venezuela and Panama its range overlaps that of the related S. undulata, or perhaps more exactly interfingers with it, for the latter is apparently adapted in equatorial latitudes to more porous sandy soils supporting a savanna climax vegetation and extends northward beyond S. quinquangulata onto the karst limestones of Yucatan. In any case within their common range S. undulata is instantly recognized at anthesis by the enlarged floral bracts and little dilated style. The largely West Indian S. viminea and wholly West Indian S. nitida are fully allopatric, the first differing in its short pod and the latter in the loss of one or two of the abaxial set of stamens. The sometimes deceptively similar S. oxyphylla has a gland between the lower pair of leaflets only.

As here delimited and as already, at least in some degree, known to Bentham, S. quinquangulata is variable in orientation, density and length of pubescence and in amplitude of the petals, although these only exceptionally and locally (e.g. Bahia, Harley et al. 17516, NY) surpass 15 mm in length. In middle Amazonia, especially around Manaus, it is represented by a race with the relatively small, strongly undulate leaflets of S. undulata, here considered taxonomically unimportant, and independently on upper Rio Branco in Terr. Roraima and in southern Mexico by forms with densely pilosulous upper branchlets and inflorescence.