Senna didymobotrya

  • Title

    Senna didymobotrya

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna didymobotrya (Fresen.) H.S.Irwin & Barneby

  • Description

    151.  Senna didymobotrya (Fresenius) Irwin & Barneby, comb. nov. Cassia didymobotrya Fresenius, Flora (Regensburg) 22: 53. 1839.—. . in Abyssinia a cl. Riippell . . ."—No holotypus survives at FR (H. J. Conert in litt. 21.1.1979); our interpretation follows, with some reluctance, that of Bentham and all subsequent literature.

    Cassia verdickii de Wildeman, Ann. Mus. Congo, Bot. Ser. 4, fasc. 2: 49, t. 16, fig. 6-11.— "Lukafu [Katanga], juillet 1900 (Ct. Verdick, n. 590)."—No typus seen.—Equated by Stey- aert, 1952, I.e. infra, with C. didymobotrya, but the plate does not show the enlarged floral bracts typical of the species and the (9-11-jugate) leaflets are fewer than normal.

    Cassia nairobensis L. H. Bailey, Hortus Second 146. 1941, nom. sine descr. lat.—Cf. Brenan, 1967, l.c.

    Cassia didymobotrya sensu Bentham, 1871, p. 551; Robyns, Fl. Spermat. Parc Nat. Albert 1: 373, pl. 37. 1948; Schery, 1951, p. 50; Steyaert, 1952, p. 504, pl. XXXVI; De Wit, 1955, p. 241; Brenan, 1967, p. 66, fig. 12; Isely, 1975, p. 80.

    Shrubs, usually several-stemmed and of broadly rounded outline, at anthesis (0.6-)1-5 m, reportedly sometimes arborescent to 9 m, the terete striate, densely leafy annotinous branchlets with foliage and inflorescence pilosulous throughout or almost so with erect or spreading-ascending white hairs up to 0.2-0.6 mm often (especially on raceme axis) mixed with random granular or longer ± flexuous thickened trichomes, the mustily foetid foliage subconcolorous, the dull-olivaceous lfts equally pubescent on both faces or rarely glabrous above, the racemes incurved to vertical from distal axils, forming a panicle at length ± exserted.

    Stipules thinly herbaceous, early reflexed, symmetrically ovate-cordate-acuminate 6-17 mm, palmately several-nerved from base, tardily deciduous.

    Lvs mostly 1-3.5(-5) dm, in expanded outline narrowly oblong-elliptic; petiole including discolored but not much swollen pulvinus (1-)1.5-4.5(-5.5) cm, at middle 1.3-3 mm diam, rounded dorsally, very narrowly margined and shallow-sulcate ventrally; rachis ±0.7-2.8(-4) dm; petiolar glands 0; pulvinules 1.2-2.7 mm; lfts (8-)9-16(-18) pairs, slightly decrescent at either end of rachis, from asymmetric base elliptic-oblong ±2-5.5(-6.5) x 0.8-2(-2.5) cm, 2.3-3 times as long as wide, at apex obtuse or broadly deltate-subacute, aristate-mucronate, the pallid margin plane, the centric straight midrib immersed above, cariniform beneath, the (6-)7-11 pairs of slender camptodrome secondary veins finely prominulous beneath, not or scarcely so above, the tertiary venulation faint, not forming a raised reticulum.

    Peduncles with tapering axis of many-fld raceme together 1-4 dm, the several fls simultaneously expanded overtopped by a cone of firm brownish or blackish- green bracts, these broadly ovate, abruptly subacute or acuminulate concave (8-) 10-17 mm, caducous; pedicels at anthesis and afterward 4-10 mm; fl-buds obliquely obovoid, densely puberulent; sepals firm, oblong-obovate, little graduated, the longest (9-) 10-14 mm; petals glabrous, yellow, fading stramineous brown-veined, little heteromorphic, beyond the short slender claw oblong or obovate, the longest 17-25(-27) mm, at anthesis all concave, forming a bowl-shaped perianth; androecium glabrous, functionally 2-merous, the anthers of 4 median stamens 2.5-3.3 mm, of 2 large abaxial ones 3-4 mm, of 1 centric abaxial one 4-5 mm, the anthers of 4 median and 1 (slightly longer) centric abaxial stamens including the pronounced porrect beak 4-5.5 mm, those of 2 large fertile ones lunately lanceolate in outline 9-11 mm, the short porrect biporose beak 0.6-1 mm; ovary densely yellowish- or pallid-pilosulous; style linear, gently incurved distally 7.5-12 mm, just below stigma 0.2-0.4 mm diam; ovules ±12-17.

    Pod stiffly ascending or randomly spreading-declined, the stipe 7-11 mm, the Unear-oblong, strongly compressed body 7-12 x (1.5-)1.7-2.3(-2.5) cm, bicarinate by the sutures, the fuscous-green, finally papery nigrescent valves finely pilosulous with short sometimes mixed with longer white hairs, corrugate by low obtuse ridges elevated over each seed, finely transverse-venulose, the locules between the narrow membranous interseminal septa 4-5.5 mm long, occupying the whole width of cavity; seeds oblong narrowed proximally, compressed parallel to the valves, 6-8.2(-"9") x 3-4.6(-"5") mm, the testa pale tan sometimes overlain with fuscous-green, smooth or obscurely pitted, moderately lustrous, crackled in age, the oblong-elliptic areole 3-4 x 0.7-1.1(-"1.5") mm.—Collections: 30.

    Savanna thickets, margin of forest galleries, lake shores and riverbanks, becoming colonial and weedy in old fields, coppiced woodland and on roadsides, widespread in tropical Africa, whence introduced into tropical and warm temperate horticulture, sporadically naturalized in s. India, Sri Lanka, Malesia, s. peninsular Florida, apparently only cultivated in s. California, Cuba, Mexico, Panama.—Fl. in N. America mostly XII-II.

    This coarsely handsome but ill-scented African senna, occasionally cultivated in North America and liable to become naturalized in frostless regions, resembles our native S. nicaraguensis and S. martiana in the narrow multifoliolate leaves and the massive erect racemes capped by a cone of dilated bracts. At anthesis it differs from both in the symmetrically cordate stipules and the less highly colored, usually fuscous rather than orange-yellow floral bracts, further from S. nicaraguensis in the short filaments of the two large abaxial stamens, and further from S. martiana in the essentially simple pinnate rather than reticulate venulation of the leaflets. The simply corrugate, not crested or umbonate pod of S. didymobotrya is decisively characteristic.