Senna bacillaris

Title

Senna bacillaris

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Senna bacillaris (L.f.) H.S.Irwin & Barneby

Description

8.  Senna bacillaris (Linnaeus f.) Irwin & Barneby, comb. nov. Cassia bacillaris Linnaeus f., Suppl. Pl. 231. 1781.—Typus infra sub var. bacillari indicatur.

Shrubs and trees with ultimately gray or whitish trunks up to 6 cm diam, in closed woodland communities becoming sarmentose, at anthesis (2-)2.5-8.5 m, the young branchlets terete striate, pliant and commonly plagiotropic or pendulous under the weight of fls and pods, all like the foliage and axis of inflorescence finely strigulose with subappressed or appressed whitish or gray hairs up to 0.05-0.25(-0.3) mm or (in Colombia and w. Amazonia) the lfts on both faces or only on lower one pilosulous with spreading-incurved lutescent hairs up to 0.3-0.6 mm, the thinly chartaceous lfts in any case bicolored, dull or sublustrously olivaceous above, paler and sometimes subglaucescent beneath, the paniculate inflorescence terminal to branchlets, leafless or at base ± leafy-bracteate, sometimes when young appearing leafy-bracteate throughout but at maturity at least partly exserted and the primary axis then becoming abruptly flexuous or zigzag.

Stipules nearly always caducous (absent from many specimens, even at young anthesis), linear straight or falcately linear-oblanceolate acute, prominently 1-few-nerved, 4.5-8(-20) x 0.4-1.3(-3) mm, rarely foliaceous falcately oblanceo- late up to 7-13 x 1-4.5 mm.

Lvs below inflorescence 12-28(-30) cm; petiole including wrinkled, usually livid pulvinus 2-5.2(-6.7) cm, at middle 1-2.4 mm diam, bluntly carinate dorsally, openly shallow-sulcate ventrally, the sulcus widened upward to the proximal pair of lfts; rachis 1.3-4.7 cm, usually a little shorter than or equalling, rarely a little surpassing the petiole; gland 1 between proximal pair, sessile or very shortly stoutly stipitate, in profile ovate-elliptic to broadly ovate obtuse (1.5-)- 1.8-4.5 x 0.8-2 mm, the body (often eaten) red or livid glabrous, pulvinules (2-)2.5-6 mm; distal pair of lfts obliquely elliptic, ovate- or (rarely) obovate- elliptic, acutely short-acuminate to broadly deltate-acuminate and obtuse, 7-19 x 3.5-9.5 cm, 1.7-2.7 times as long as wide, at base on proximal side rounded to cordate, on distal side more shallowly rounded to cuneate, the margin (of mature blades) plane, the incurved midrib slightly raised above, cariniform beneath, the (6-)7- 12(- 14) pairs of major camptodrome with intercalary secondary veins and all tertiary venules subequally prominulous on both faces, the subsequent reticulation variable, but ± equally prominent on both faces; proximal pair of lfts ±1/2-2/3 as long as the distal, proportionately broader, very obliquely ovate, the midrib strongly displaced and the proximal basal angle broadly cordate-rounded.

Racemes solitary, 5-35-fld, the expanded fls subcorymbose, the axis including short stout peduncle (1.5-)2-7(-8.5) cm; bracts caducous from below young fl- buds, usually before elongation of pedicel, ovate or lanceolate 0.8-2.5(-3) mm; pedicels at and after full anthesis (2-)2.5-5(-5.5) cm; young buds subglobose, densely gray- or yellowish-strigulose or pilosulous, opening long before true anthesis; sepals thinly herbaceous often membranous-margined, greenish, yellowish, or red-flecked, little graduated, all obovate or broadly elliptic-oblong obtuse, the longest inner ones 8-11.5(-12.5) mm; petals pale or golden-yellow, puberulent both dorsally and (at least thinly) ventrally, the 3 adaxial subhomomorphic except the sometimes broader vexillar one, beyond the claw obovate, oblong-obovate, of flabellate, the longest (16-) 18-30(-32) mm; the 2 abaxial commonly narrower and shorter, one ± oblique; androecium functionally 6-7-merous, the filaments puberulent or sometimes glabrous, those of 4 median anthers clavate- or bulbous- dilated distally (or almost throughout) 1.2-2.5 mm, those of 2-3 abaxial ones filiform 2.5-5 mm; anthers usually puberulent in the grooves, sometimes thinly so overall, those of 4 median stamens slightly incurved, up to 5.5-10 mm, with very short divaricate 2-porose beak 0.4-0.7 mm, those of 2-3 abaxial ones much more strongly lunate-incurved, the body shorter than that of the longest of the median ones, 4-8.5 mm, with porrect 1-porose beak 1.4-2 mm; ovary densely strigulose; style scarcely dilated, 0.6-1.2 mm diam at the bend just below the stigma, this 0.3-0.45 mm diam; ovules 122-266.

Pod pendulous, stipitate, the stout stipe 3-8(-10) mm, the straight or slightly decurved cylindric or (fully ripe) obtusely 4-angular body (10-) 14-36 x 0.9-1.4 cm, the sutures 1.2-2.6 mm wide, the valves stramineous or brown when ripe, smooth or coarsely low-venulose, glabrescent, the thickened margin along the sutures 0.5-3 mm wide; dehiscence follicular, before falling, the valves gaping to expose the seeds embedded in foetid pulp; seeds biseriate, turned broadside to the septa, compressed-ovoid, 3.2-5.6 x 2.2-3.5 mm, the atrocastaneous, usually lustrous (rarely dull) testa either smooth or finely pitted around the long diam, a faint but definite areole on each face 2.6-4.4 x 1.7-2.4 mm.

The syndrome of characters that defines S. bacillaris sens. lat. consists of a) reticulately venulose plane-margined leaflets, the proximal pair half-cordate at the strongly oblique base; b) a paniculate inflorescence with abruptly flexuous primary axis; c) relatively large sepals and petals; d) 1-pored abaxial anthers; e) a multiovulate pod broadly margined along the sutures; and f) biseriate, faintly areolate seeds. The several closely related species which have been and often still are confused with S. bacillaris differ from it in one or more of these features, as brought out in greater detail under each.

The native range of S. bacillaris is primarily northern South American, and we believe that it is only planted northward from southern Nicaragua and the southern Windward Islands, though common in cultivation and locally naturalized throughout most of Antillia. The common species which have passed as Cassia bacillaris in Mexico and Central America are S. fruticosa, S. papillosa and S. hayesiana. All have more or less distinctly revolute leaflets; in addition S. hayesiana is instantly distinguished by its 4-merous androecium, S. fruticosa by its smaller flowers, fewer ovules and smooth glossy pod not marginally differentiated parallel to the sutures, and S. papillosa primarily by the distinctive pod, unmargined as in S. fruticosa but densely papillate overall. Of these three, only S. fruticosa has similarly areolate seeds.

We here recognize two varieties of S. bacillaris, distinguished by a small difference in the androecia supported by almost fully vicariant ranges.