Senna mollissima (Humb. & Bonpl. ex Willd.) H.S.Irwin & Barneby

Authors

Howard S. Irwin, Rupert C. Barneby

Authority

Irwin, Howard S. & Barneby, Rupert C. 1982. The American Cassiinae. A synoptical revision of Leguminosae tribe Cassieae subtrib Cassiinae in the New World. Mem. New York Bot. Gard. 35, part 2: 455-918.

Family

Caesalpiniaceae

Scientific Name

Senna mollissima (Humb. & Bonpl. ex Willd.) H.S.Irwin & Barneby

Type

Typus infra sub var. mollissima indicatur.

Synonyms

Cassia mollissima Willd.

Description

Species Description - Amply leafy arborescent shrubs at anthesis 3-10 m, the main trunks attaining ±5-6 cm diam, the annotinous and older branches gray or pale brown lenticellate, the hornotinous branchlets and foliage pilosulous throughout with fine, simply or sinuously incurved or sometimes straighter spreading-ascending hairs up to 0.3-0.6(-0.7) mm, the dull olivaceous bicolored lfts pale and densely softly pubescent beneath, the vesture of their upper face thinner and shorter (the hairs sometimes basally dilated), of the emergent foliage often lutescent, the loose racemes axillary to and shorter than coeval lvs, pliantly pendulous. Stipules erect firm, narrowly lanceolate or subulate 2.5-5.5 x 0.3-0.7 mm, early dry, deciduous before the lf. Longer lvs when fully expanded (l-)1.5-4(-4.7) dm; petiole including wrinkled pulvinus (3-)4-13 cm, at middle 0.9-2 mm diam, subterete, obtusely 2-ribbed and very shallowly grooved ventrally; rachis (1.5-)2.5-21 (-24) cm; petiolar gland 0; pulvinules (1.5-)3-6.5 mm; lfts of larger lvs 2-6 pairs accrescent distally, ovate, ovate-elliptic or elliptic short-acuminate 6-16 x (2.5-)3-7(-7.5) cm, 1.7-3 times as long as wide, at base subsymmetrically cuneate or rounded, the margin revolute, the midrib immersed or shallowly depressed above, cariniform beneath, the 9-12 pairs of slender camptodrome and random intercalary secondary veins with connecting tertiary and often loosely reticular venules all pallid and sharply finely prominulous beneath, faintly so or immersed above; shorter proximal pair of lfts often proportionately broader, ovate-acuminate. Racemes 15-125-fld, the several fls fully or partly open often but not always surpassed by succeeding fl-buds; bracts ovate- or lance-acuminate or -caudate 2-3.3(-4) x 0.8-1.2 mm, firm but early dry and deciduous before anthesis; pedicels at anthesis very slender, flexuous and often refracted from the pendulous axis (heliotropic), much thickened in fruit, at and after full anthesis 12-23 mm; young fl-buds globose pilosulous, the early emergent inner sepals dorsally glabrous or glabrescent ciliolate; sepals thinly herbaceous greenish, well graduated, the outermost elliptic-obovate 4-5.5 mm, the innermost broadly obovate-subor- bicular (5.5-)6-8 mm; petals glabrous yellow drying brownish-stramineous, coarsely brown-veined, highly heteromorphic, the 3 adaxial smallest, oblong-obovate or -oblanceolate obtuse 10-19 x 4-7 mm, one abaxial like the latter in outline but larger, 13-20 x (6-)8-11 mm, opposed to the oblique pistil, the other abaxial one coarsely short-clawed and incurved through nearly 90°, concave and incurved over the androecium, measured along the arcuate midrib 19.5-36 x 10-18.5 mm; androecium glabrous, functionally 7-merous, the 3 staminodes 1.2-1.7 mm wide, the fertile stamens almost isomorphic, parallel and contiguous, their stout filaments 1.5-3.2 mm, the anthers oblong or slightly dilated upward, obtusely rounded at both ends, nearly straight, in dorsal view (4-)4.5-6.6 x 2-2.6 mm, the connective on ventral side dilated distally so as to separate the thecae, these abruptly contracted into a divaricate beak 0.3-0.8(-l) mm, each dehiscent by a short vertical slit; ovary glabrous or very sparsely pilosulous; style often scarcely differentiated externally from the ovary, 2-3 mm long, gently incurved distally and abruptly contracted to the minute terminal stigmatic cavity, at base of the conical tip 0.5-0.9 mm diam; ovules 52-96. Pod pendulous from pliantly pendulous raceme axis, the stipe 2-6 mm, the linear compressed but thick, tapelike, usually straight body 20-40 x (1-) 1.2-1.5(-1.9) cm, the stout obtuse sutures a little broader than the cavity (the cross section hence dumbbell-shaped), the firmly coriaceous purplish- or livid- brown, ultimately nigrescent valves not or scarcely elevated over seeds, their margins thickened, internally pithy and at maturity splitting transversely at intervals of 1-2.5 mm, the seed-locules 4-6 mm long, not extending into the thickened margin, the ripe valves finely sharply venulose, not dehiscent lengthwise but fragile and easily broken along the transverse interseminal septa, the seeds apparently released only by weathering; seeds oblong-obovoid moderately compressed 5.8-7.2 x 3.5-4.2 mm, the smooth or remotely pitted, light reddish- brown testa dull, the glossy obtusely rhombic or oblong-elliptic areole 2.5-3.7 x 2-2.5 mm.

Variety Key - Key to the Varieties of S. mollissima 1. Longer lvs 2-4.7 dm, their rachis (8-)12-24 cm, the lfts (3-)4-6 pairs; racemes (25-)30-125- fld, the axis becoming 1-4 dm; oblique abaxial petal, measured along its curved midrib, 19-24 mm; Pacific Mexico (Sinaloa to w. Oaxaca); s.-e. Guatemala. 200a. var. glabrata (p. 594). 1. Longer lvs (1.1 -) 1.5-2.5(-2.8) dm, their rachis (1.5-)2.5-12(-14) cm, the lfts 2-4(-5) pairs; racemes 15-35-fld, the axis becoming 5-18(-23) cm; oblique abaxial petal 26-36 mm; n.-w. Peru and s. Ecuador. 200b. var. mollissima (p. 595).

Discussion

Our concept and definition of S. mollissima coincide with those developed in herbaria and in post-Benthamian literature under the name Cassia atomaria. Following Britton & Rose we equate genuine Linnaean C. atomaria with C. emarginata auct. (not Linn.) and consequently revive for C. atomaria in the sense of Bentham and most modern floras the next available epithet mollissima. Senna mollis sima is very closely related to S. atomaria, of which it has the pod and seeds, and differs principally from it only in the ampler, acuminate rather than obtuse or abruptly acute leaflets and larger, commonly more numerous flowers produced always from axils of coeval leaves, never from old wood. From a theoretical viewpoint these are weak differential characters. In practice, however, Mexican var. glabrata, the range of which lies within the western lobe of that of S. atomaria, has very much larger leaves and much longer racemes than its sympatric relative; while var. mollissima of northern Peru and southern Ecuador is at once allopatric and much larger-flowered. Between the Mexican and South American populations, which are similar in gross aspect and have both passed as C. atomaria in recent literature, we find several small but significant differences which enable us to define in morphological terms two mutually remote geographic varieties. Key to the Varieties of S. mollissima 1. Longer lvs 2-4.7 dm, their rachis (8-)12-24 cm, the lfts (3-)4-6 pairs; racemes (25-)30-125- fld, the axis becoming 1-4 dm; oblique abaxial petal, measured along its curved midrib, 19-24 mm; Pacific Mexico (Sinaloa to w. Oaxaca); s.-e. Guatemala. 200a. var. glabrata (p. 594). 1. Longer lvs (1.1 -) 1.5-2.5(-2.8) dm, their rachis (1.5-)2.5-12(-14) cm, the lfts 2-4(-5) pairs; racemes 15-35-fld, the axis becoming 5-18(-23) cm; oblique abaxial petal 26-36 mm; n.-w. Peru and s. Ecuador. 200b. var. mollissima (p. 595).