Senna roemeriana

Perennial herbs from tough blackish woody root, at anthesis (1.5-)2-7 dm, the 1-several erect or assurgent, simple or few-branched, distally sulcate stems with all lf-stalks and axes of inflorescence densely minutely pilosulous with fine erect or subretrorse hairs usually mixed with scattered ascending or antrorsely accumbent setules up to 0.2-0.7 mm, the 2-foliolate lvs ± bicolored, yellowish-green above and pallid- or bluish-green beneath, the lfts usually strigulose or antrorsely pilosulous on both faces, sometimes only thinly so or glabrous above, the axillary racemes at first lateral and shorter than or subequalling the subtending lf, later forming a shortly exserted corymbose panicle.

Stipules widely ascending linear-attenuate or setiform 3-9(-11) x 0.2-0.4(-0.5) mm, at first green, early dry caducous, lacking from most fruiting specimens.

Lvs 2.5-9.5 cm; petiole including the firm, scarcely swollen pulvinus 1-3(-3.8) cm, at middle 0.3-0.8(-1) mm diam, the shallow ventral groove almost closed; gland between the 1 pair of lfts, shortly stipitate or subsessile, in profile (0.3-) 0.6-1.6 mm, the stipe puberulent, the narrowly fusiform or lance-subuliform orange (much eaten) head 0.1-0.35 mm diam; pulvinules discolored 0.9-1.8(-2.2) mm; lfts ascending subvertically from petiole, in outline narrowly lance-oblong or lanceolate acute, obtuse mucronulate or apiculate, the larger ones (2-) 2.5-6(-7) x 0.4-1.2(-l.4) cm, (3.6-)4-8(-9) times as long as wide, at base cordate on proximal and cuneate on distal side, the margin plane, the midrib immersed above, prominent beneath and there giving rise, often on broader side of lft only and not above 2/3 from base of blade, to 1-5(-6) weak secondary veins, these usually expiring well within the margin and short of anastomosis, the upper face of blade essentially veinless.

Racemes loosely but shortly (l-)2-5-fld, the peduncle and axis together 2.5-6.5(-8) cm; bracts linear-attenuate 1.5-5 mm, deciduous at or before anthesis; pedicels 9-16 mm; fl-buds horizontal or nodding, subglobose becoming obovoid, thinly strigulose-pilosulous; sepals submembranous pallid or tinged with pale green or pinkish-brown, of nearly equal length but varying from narrowly elliptic to obovate, the longest 5.5-7.3(-8.2) mm, all deciduous with the corolla; petals yellow or orange-yellow, wilting after one day, drying stramineous or whitish brown-veined, of subequal length or the vexillar one slightly shorter, obovate- cuneate obtuse or openly widely emarginate, including short claw (11-) 12-16(-17) x (4-)5.5-11 mm; androecium glabrous, the staminodes narrowly oblanceolate or spatulate, the 7 fertile members similar in form but graduated in length, the 2 next the staminodes shortest, their filament 1.5-2.5, their anther 1.7-2.4 mm, the 2 latero-abaxial longest, their filament 2.6-4.5, the anther (2.2-)2.5-3.3 mm, the 3 others intermediate, the anthers of all lunately oblong or lance-oblong in profile 0.5-0.8 mm diam, strangulated just below apex and thence slightly dilated into the subsymmetrically terminal pore, their walls thin bicolored, castaneous along connectival grooves, yellow laterally; ovary densely white-pilosulous; style glabrous, gently incurved, linear or a trifle narrowed distally 1.2-2.4 mm, at apex 0.1-0.25 mm diam, the minute stigmatic cavity symmetrically terminal, ciliolate; ovules (22-)26-40.

Pod erect or narrowly ascending, linear-oblong or narrowly oblong-oblanceolate in profile, straight or gently incurved, (20-)23-32(-35) x (0.45-)0.5-0.65 mm, laterally compressed but strongly turgid, the green or red-tinged valves thinly setulose with appressed or subappressed stiff hairs up to 0.5-0.8(-l) mm, becoming firmly papery dark brown but paler along the wide sutural margins, at middle low-corrugate over the seeds, dehiscent downward through both sutures, the cavity broadly membranous-septate, the whole pod often long persisting, even on dead dry stems; seeds turned fully or obliquely to face the septa, stacked closely into 2 separate parallel or incipiently interdigitating files, often distorted by crowding, the perfect ones compressed-pyriform or paddle-shaped 2.53.3 x 1.7-2.7 mm, the moderately lustrous testa brown, pinkish-brown or when long ripe graying and crackled, densely sinuously rugulose-colliculate overall, the elliptic or round areole 0.4-0.7 x 0.4-0.6 mm; n — 14.—Collections: 76.—Fig. 10 (androecium), 14 (pod, seed).

Mesquite-grassland, chaparral, ascending w.-ward into draws in short-grass prairie and barren hillsides and washes of n. Chihuahuan Desert, 200-2050 m, widespread and locally abundant over most of centr. and trans-Pecos Texas, especially vigorous and common on limestones of Edwards Plateau, extending n. to the Red River in s. and s.-w. Oklahoma, up the Pecos River valley in New Mexico to Quay County and the White Mountains, s. just into n.-e. Chihuahua, centr. Coahuila, and n.-centr. Nuevo Leon; one station w. of the Rio Grande in s.-w. New Mexico (Sierra County).—Fl. IV-IX(-X).

A senna widespread and familiar in the arid grasslands and mesquite plains of southwestern United States and northeastern Mexico, where it is distinguished from other bifoliolate Brachycarpae by the long, proportionately narrow leaflets combined with a linear style. It is closely akin only to S. mensicola, next following, which see for comment.