Senna bauhinioides (A.Gray) H.S.Irwin & Barneby
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Authors
Howard S. Irwin, Rupert C. Barneby
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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 1: 1-454.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Lectotypus (Isely, 1975, p. 198), Wright s.n., GH! paratypi, Wislizenus s.n. GH! Gregg s.n., NY (hb. Torr., adnot. Benth.)!—Earleocassia bauhinioides (A. Gray) Britton ex Britton & Rose, N. Amer. Fl. 23(4): 248. 1930.
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Synonyms
Cassia bauhinioides A.Gray, Earleocassia bauhinioides (A.Gray) Britton, Cassia bauhinioides var. arizonica C.B.Rob. ex J.F.Macbr.
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Description
Species Description - Precociously flowering perennial herbs from blackish taproot, the 1-few erect or diffuse stems simple or branched below middle, at anthesis (0.6-) 1-3(-3.5) dm, the stems and lf-stalks densely pilosulous with shorter, retrorsely accumbent soft hairs and stiffer, spreading or incurved-ascending setulose ones up to (0.2-) 0.3-0.8(-1) mm, the lfts pilosulous on both faces with incurved, sinuous or straight subappressed hairs, the stems in addition and lft-margins rarely bearing a few (many) fine spiral setae up to 2.5 mm, the foliage almost concolorous but the upper face of lfts sometimes yellowish- and the lower bluish-green, the 1-3- fld racemes axillary and lateral, all but the latest subterminal ones shorter than their accompanying lf. Stipules at first ascending, often spreading-reflexed in age, narrowly lance-attenuate, linear-caudate or setiform 2.5-7 x 0.3-0.6 mm, becoming dry and tardily deciduous. Lvs 1.5-5.5 cm; petiole (0.5-)0.8-2.6(-3.2) cm, at middle 0.3-0.65 mm diam, obscurely ribbed dorsally, the ventral groove shallow and almost closed; gland between the one pair of lfts stipitate or subsessile, in profile (0.5-)0.6-1.4 mm, the stipe usually pilosulous, slender or rarely incrassate and thicker than the head, this (much eaten) slenderly (plumply) ovoid or lance-fusiform acute 0.1-0.3(-0.5) mm diam; pulvinules 0.5-2 mm; lfts obliquely oblong or ovate-oblong obtuse mucronulate or deltately apiculate (8-)12-36(-46) x 5-13(-16) mm, 2-3.7(-4.1) times as long as wide, at base deeply cordate on proximal and cuneate on distal side, the margin plane, the blade veinless above, the midrib prominulous beneath and commonly giving rise to 1-3 secondary veins palmately radiating into the cordate base of blade and sometimes on the same or on both sides to l-3(-4) weak pinnate ones, these expiring well short of anastomosis. Peduncles ascending 6-30 mm, all 1- or most (all) 2-3-fld, the raceme-axis 0-6(-8) mm; bracts resembling stipules but only 1.5-4 mm; pedicels 3-9(-11) mm; fl-buds when young nodding subglobose pilosulous; sepals thinly herbaceous, membranous where covered in bud, elliptic or obovate-elliptic obtuse, scarcely graduated, the innermost (4-)4.5-6.5(-7) mm, all deciduous with the petals; petals glabrous or externally puberulent at the claw, yellow drying whitish brown- veined, obovate-cuneate (5-)6-9(-10) mm, sometimes not fully expanding but if so lasting only one day; androecium glabrous, functionally 7-merous, the fertile members accrescent toward the abaxial side of fl, the 2 next to the minute spatulate staminodes shortest, their filament 1.1-1.8 mm, their anther 1.5-2 mm, the 2 latero-abaxial (oppositipetalous) longest, their filament 2.5-4 mm, their anther (1.8-)2-2.8 mm, the 3 other intermediate, the anthers of all narrowly oblong obtuse, lunately incurved 0.6-0.8 mm diam, dehiscent at apex by an obliquely terminal pore, their walls thin-textured bicolored, castaneous along the connec- tival grooves, yellow laterally and there only obscurely sulcate; ovary densely white-pilosulous; style incurved from ovary (0.5-)0.7-1.4 mm, distally dilated into a symmetrically or obliquely truncate membranous-margined stigmatic cavity 0.4-0.6 mm diam; ovules (22-)25-36. Pod ascending or (from prostrate stems) humistrate, sessile or almost so, in profile narrowly oblong to oblong-oblanceolate, lunately incurved or rarely straight, abruptly contracted at apex into a short subulate beak, the strongly turgid body 17-30 x 4.5-6.5 mm, the thin green puberulent and setulose valves early dry brown and papery, differentiated into a central darker band low-corrugate over the seeds and broad paler sutural margins, dehiscent downward through both sutures, the interseminal septa broad membranous castaneous, the whole dehisced pod long-persistent on the drying stems; seeds turned with broad faces to the septa, stacked into 2 crowded files and often distorted by mutual pressure, the perfect ones compressed-pyriform or paddle-shaped (2.2-)2.4-3.2 (-3.7) x 1.8—2.3(—3) mm, the testa brownish-olivaceous becoming when fully ripe gray or pinkish-gray and crackled, sinuously colliculate-rugulose overall, the round or elliptic areole 0.35-0.5 x 0.25-0.4 mm.—Collections: 53.
Distribution and Ecology - Stony hillsides, plains, bajadas, gullied bluffs along streams or dry washes, sometimes prolifically colonial on roadsides, mostly in Larrea scrub, mesquital or desert grassland at 500-1800 m, widespread over the n. Chihuahuan Desert and around the margins of the Gila Basin in s.-e. Arizona, immediately adjoining Sonora, s. New Mexico and trans-Pecos Texas s. to centr. Coahuila, extending feebly n. in Arizona to the Little Colorado River (Coconino Co.) and in Texas and presumably adjoining Mexico s.-e. along the Rio Grande and down to ±80 m as far as Starr County n. of the border and the e. piedmont of Sa. Madre Oriental in n.-centr. Nuevo Leon.—Fl. IV-XI, and even through winter if moisture permits.
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Discussion
From the viewpoint of floral specialization S. bauhinioides is the most advanced of ser. Brachycarpae. The short funnel-shaped style upturned to receive pollen from the accompanying anthers and the small ephemeral corolla that sometimes fails to expand fully before fertilization are sure signs of autogamy. The species consists of populations internally very uniform in details of vesture and ovule-number but different among themselves in these features, a situation that is perpetuated by self-fertilization and the development of pure lines of inheritance. Like many xerophytic herbs, S. bauhinioides responds quickly to rainfall at any season of the year. Plants a few weeks old bearing flowers and fruits might be mistaken for monocarpic and perhaps do sometimes perish in the first season. Normally, however, they will survive two or several periods of quiescence brought on by either cold or drought or both, becoming clearly perennial though never developing a true caudex.
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Distribution
Arizona United States of America North America| New Mexico United States of America North America| Texas United States of America North America| Coahuila Mexico North America|