Senna covesii (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
Lectoholotypus (Isely, 1975, p. 201), Coues & Palmer 171, GH!—Earleocassia covesii (A. Gray) Britton ex Britton & Rose, N. Amer. Fl. 23(4): 249. 1930.
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Synonyms
Cassia covesii A.Gray, Earleocassia covesii (A.Gray) Britton
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Description
Species Description - Precociously flowering perennial, in age weakly suffrutescent herbs of bushy outline arising from stout lignescent dark brown or blackish root, the (1-) 2-several simple or proximally few-branched stems at anthesis 2-6.5 dm, densely gray-pilosulous throughout with shorter soft subappressed and longer ascending- spreading hairs, the short vesture of stems retrorse, elsewhere forwardly accumbent, the longer hairs up to 0.5-1 mm or rarely some setiform to 1.5-2.5 mm (occasionally almost 0), the foliage bicolored, the lfts yellowish-green above, pallid beneath, the inflorescence of axillary few-fld racemes arising from many successive axils over a long season, the fls raised beyond the subtending lf. Stipules erect or spreading linear-attenuate or setiform (3.5-)4.5-8 (-11) x 0.2-0.6 mm, the rather firm blades persisting into maturity of lf, then dry deciduous. Primary lvs (2-)3-8.5(-10) cm; petiole including poorly differentiated pulvinus (0.5) 1-3.5 cm, at middle 0.5-1 mm diam, shallowly openly sulcate ventrally; rachis 0.5-2.5(-3, seldom over 2) cm, its setiform appendage early caducous; petiolar glands (much eaten) always between proximal, commonly between all pairs, stipitate, in profile (0.5-)0.9-2.5(-3.5) mm, the stipe pilosulous, the slenderly fusiform acute reddish head 0.1-0.2 mm diam; pulvinules (0.5-)0.8- 1.6(-2) mm; lfts 2-4, in most plants 2 and 3, in some 3 and 4, exceptionally in all lvs exactly 2 pairs, accrescent distally (but the penultimate pair sometimes largest), the distal pair broadly obovate, elliptic-obovate or oblong-elliptic obtuse mucronulate or deltately apiculate (1-) 1.4-3(-3.8) x (0.55-)0.7-1.7(-1.9) cm, (1.4-) 1.6-2.4 times as long as wide, at oblique base broadly rounded or cordate on proximal side, the margin plane, the midrib and (3-)4-6(-7) pairs of secondary veins weakly prominulous beneath, fully immersed above, the secondary veins usually expiring intramarginally before anastomosis. Peduncles stiffly ascending (2-)3-8 cm; racemes shortly or subumbellately (2-)4-8(-10)-fld, the axis becoming (0.5-) 1-3.5 cm; bracts linear-lance-attenuate 3-7 x 0.4-1 mm, caducous well before anthesis; pedicels at and after anthesis 8-17 mm; fl-buds obovoid pilosulous; sepals submembranous pale green, pinkish or yellowish, glabrate and hyaline where covered in bud, in outline elliptic-oblong, -obovate or -oblanceolate obtuse, little graduated, 5-7.6 x 2.4-3.4 mm, deciduous with or soon after the petals; corolla, androecium and pistil exactly zygomorphic, petals golden-yellow drying stramineous dark-veined, isomorphic except the 2 abaxial a trifle narrower, all ± broadly obovate beyond the short claw (9-) 10- 14(- 15) x 4.5-9(-10) mm; androecium glabrous except sometimes puberulent at base of filaments, functionally 7-merous, the 3 adaxial staminodes pallid oblanceolate 1.5-3.5 mm, the 7 fertile stamens isomorphic except the pair next the staminodes a little shorter, the filaments 1.8-3 mm, the linear-lanceolate, gently incurved anthers 2.5-4.2 x 0.6-0.9 mm, brownish but yellowing in the lateral grooves, just below conic-obtuse apex faintly constricted, terminally dehiscent by a single obliquely introrse pore; ovary densely white-pilosulous; style glabrous filiform or slightly tapering distally 2-3.1 mm, incurved from ovary thence almost straight, at apex 0.1-0.2 mm diam, the minute stigmatic cavity terminal; ovules (28-)30-38(-42). Pod erect subsessile, in profile narrowly oblong-elliptic or oblanceolate, gently incurved or almost straight, the body (18-)20-32(-34) x 5-7.5(-8) mm, abruptly contracted distally into an erect subulate beak 2-3.5 mm, a little laterally compressed but strongly turgid, the cross section broadly elliptic, the green or reddish valves pubescent with fine short and longer appressed or ascending setiform hairs up to 0.5-0.8 mm, becoming papery and differentiated lengthwise into broad pallid sutural margins and a brown or nigrescent band shallowly corrugated over the seeds, dehiscent through beak and downward, narrowly gaping to release the seeds; seeds stacked horizontal to pod’s long axis into 2 interdigitating ranks, each turned with broad faces to its neighbors, all closely contiguous at the hilar end but separated distally by incomplete endocarpic septa (fleshy when fresh, castaneous membranous when dry), their broad faces basically paddle-shaped but often distorted by crowding, (2.5-)2.7-3.7 x 1.9-3 mm, irregularly carinate around periphery, the faces variably coarsely undulate-rugose, the smooth sub- lustrous testa fawn- or pinkish-brown, crackled when old, the round or elliptic areole 0.3-0.5 x 0.2-0.3 mm.—Collections: 52.
Distribution and Ecology - Sandy and gravelly flats, washes and stony hills with Larrea and Prosopis or in cactus-thorn-forest, 10-1125 (mostly below 800) m, commonly and widely dispersed over the floor of the Sonoran Desert in the basin of the Gila River in s. and w. Arizona, extending weakly into extreme s.-w. New Mexico, n. along the Colorado River just into Clark Co., Nevada and by way of Grand Canyon into Coconino Co., Arizona, w. becoming less common to the n. and w. edges of the Colorado Desert in e. Riverside and San Diego counties, California, and s. along the coastal plain from the n.-e. corner of Baja California Norte through Sonora to the Fuerte valley in n.-w. Sinaloa.—Fl. prolifically in spring and fall, but intermittently through the year, the pods persisting indefinitely even on dead stems.
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Discussion
Senna covesii and S. confinis, a closely related vicariant pair of species adapted to austere desert climates, are distinguished among Brachycarpae with retrorsely hairy stems and 2-4-jugate leaflets by glandless stipules, crumpled seed-face, and ecology. Of the two S. covesii is the more slender and more freely branching plant, becoming a small bush in age. Its leaflets are commonly more than two, not exactly two pairs, and smaller, its pods are appressed-setulose and not hispid, and the testa of the somewhat smaller seeds is simply crumpled into coarse folds but not further colliculate. The erect pods of both these sennas persist on the old dying or dead stems long after dehiscence and the seeds are shaken out of the gaping valves in the so-called censer fashion. Coues’s senna—it was dedicated by Asa Gray to the ornithologist Elliott Coues, 1842-1899—was first collected by Sesse or some other member of the Spanish expedition to New Spain, presumably either in Sonora or Sinaloa in 1791-1792, and was shortly thereafter in cultivation at the Madrid Botanical Garden under the unpublished name "planiflora." It is, however, not to be recognized among the cassias described in either of Sesse’s posthumously published floras. In the Desert House at New York Botanical Garden it is cultivated without difficulty or special attention, its thin gray foliage and golden yellow flowers forming a quietly effective picture almost throughout the year.
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Distribution
Arizona United States of America North America| New Mexico United States of America North America| Nevada United States of America North America| Baja California Mexico North America| California United States of America North America| Sinaloa Mexico North America|