Senna armata

  • Title

    Senna armata

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna armata (S.Watson) H.S.Irwin & Barneby

  • Description

    90.  Senna armata (S. Watson) Irwin & Barneby, comb. nov. Cassia armata S. Watson, Proc. Amer. Acad. Sci. 11: 136. 1876.—. . found by Dr. J. G. Cooper in the mountains of S. California, between Fort Mohave and Cajon Pass, and also by Lieut. Wheeler in W. Arizona."—Lectoholotypus (Isely, 1965, p. 197): Wheeler s.n. GH! paratypus, Cooper s.n. (fragm), GH!—Xerocassia armata (S. Watson) Britton & Rose, N. Amer. Fl. 23(4): 246. 1930 (the ‘type locality’ retroactively incorrect).

    Cassia armata sensu Jepson, 1936, p. 241, fig. 175; McMinn, 1939, p 229, fig. 258; Jaeger, 1936, fig. 212; Munz & Keck, 1959, p. 800; Kearney & Peebles, 1960, p. 405; Wiggins in Shreve & Wiggins, 1964, p. 615; Isely, 1975, p. 64, map 17.

    Sparsely leafy, by midsummer leafless and junceous, softly woody or merely suffruticose, freely branched xeromorphic bushy herbs or subshrubs of rounded outline, at anthesis 4-14 dm tall and up to 1.5 times as wide, the hornotinous stems clad in a dense coat of minute lustrous, retrorsely appressed, at first silvery later lutescent hairs, the foliage and inflorescence glabrate or thinly puberulent with looser or forwardly appressed hairs to 0.2-0.45 mm, the small fleshy green distant lfts early deciduous from thickened recurving lf-stalks, the inflorescence a long narrow far-exserted panicle of sessile (or subsessile) 1-2-fld racemes subtended by diminished lvs or linear phyllodes.

    Stipules 0.

    Lvs below the inflorescence mostly 2-8(-9) cm, the obscure pallid pulvinus inactive, the pulvinules almost 0, the fleshy green lf-stalks rounded dorsally, flattened and not or very obscurely sulcate ventrally, (0.4-)0.6-1.6(-2) mm wide, tapering distally into a sharp dry but not vulnerant point or exceptionally expanded into a linear blade; petiolar gland usually 0, exceptionally rudimentary, then inserted on rachis above first 1ft; lfts (0-)2-8(-10), either paired or irregularly inserted along rachis, the first often inserted next to pulvinus, all sessile or almost so or exceptionally confluent with lf-stalk, decrescent upward, the plane, essentially veinless blades obliquely ovate, rhombic-ovate or ovate-reniform, obtuse or subacute, the longest 2-9 x 1-6 mm, at base obliquely cuneate or semicordate- auriculate.

    Peduncles obsolete (exceptionally to 5 mm), the fls appearing axillary, solitary or paired; bracts linear-subulate 0.8-3 mm caducous; pedicels slender, widely ascending (8-)9-21 mm, little thickened in fruit; fl-buds ascending-spreading, plumply obovoid obtuse, glabrous or thinly puberulent; sepals submembranous often petaloid, yellowish or fuscous-yellow with pale margins, little graduated in length, elliptic- or oblong-obovate obtuse, the longest 5-7 mm; petals golden- yellow, dark-veined when dried, glabrous, subhomomorphic except the 2 abaxial sometimes a trifle longer than the rest, obovate-cuneate or flabellate, the longest (7.5-)8-11.5(-13) mm; androecium glabrous, functionally 7-merous, the fertile stamens not differentiated into two sets but slightly accrescent abaxially. the filaments 1-2.2(-2.6) mm, the anthers in profile slenderly lanceolate, slightly incurved, 3-4.3 mm, either gradually tapering distally or commonly a trifle constricted 0.3-0.6 mm below the obliquely truncate terminal pore; ovary strigulose, sometimes thinly so; style slenderly subulate incurved 1.1-2 mm, at apex 0.1-0.2 mm diam; ovules 6-12, usually only 2-5 maturing.

    Pod stiffly ascending, linear-ellipsoid (2-)2.5-4.5 x (0.45)-0.5-0.65 cm, tapering at base into an almost obsolete stipe and at apex into the persistent style- base, at first compressed but becoming strongly turgid at maturity, then obtusely carinate by the sutures, the papery brown sublustrous glabrescent valves slightly paler and thickened toward the sutures, obscurely venulose at the middle, the interseminal septa almost obsolete; dehiscence apical and downward through the sutures, long delayed; seeds basipetally descending along the pod’s long axis, plumply obovoid and variably distorted by crowding or incipiently folded and ridged, the testa smooth or finely pitted, dull fawn- or darker brown, crackled, the excentric areole circular ±0.3 mm diam.—Collections: 39.—Fig. 11 (androecium), 14 (pod, seed).

    Desert washes and outwash fans of desert mountains, in the Larrea zone, 150-1100 m, locally abundant and common over the Mohave Desert s. from Amargosa Valley, Inyo Co., California and s. half of Clark Co., Nevada to the Salton Basin and Colorado trench in interior Riverside, San Diego and Imperial cos., weakly e. into Mohave Co., Arizona, and along the e. margin of Colorado Desert s. into n. Baja California.—Fl. (III-)IV-VI, the fruits long persisting on leafless and withered stems.