Senna pumilio

  • Title

    Senna pumilio

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna pumilio (A.Gray) H.S.Irwin & Barneby

  • Description

    88.  Senna pumilio (A. Gray) Irwin & Barneby, Phytologia 44(7): 500. 1879. Cassia pumilio A. Gray, Boston J. Nat. Hist. 6(2): 180. 1850.—"[Lindheimer s.n.] . . . On the Llano and Pierdenales [=Pedernales rivers, Texas]. ‘Only two small specimens seen.' Rio Grande, Texas, Mr. Charles Wright."—Lectoholotypus, Wright 412 from Llano and Pedernales rivers, May, Oct. 1847, GH (top right of sheet, which contains also an unnumbered collection of Lindheimer (fasc. IV) lacking locality, Wright s.n. from Rio Grande in 1848, these considered paratypi, and

    collections posterior to 1850); Wright 153, FI, NY, dated 1849, are not considered paratypic.—Tharpia pumilio (A. Gray) Britton & Rose, N. Amer. Fl. 23(4): 247. 1930.

    Cassia pumilio sensu Bentham, 1871, p. 529 (erroneously attributed to New Mexico, a misconception long perpetuated); Turner, 1959, p. 73, map 34 (Texas); Isely, p. 120, map 54 (Texas).

    Small tufted acaulescent or shortly caulescent perennial herbs from blackish subterranean caudex and oblique, irregularly thickened or fusiform woody roots, at anthesis (3-)4- 12(-17) cm tall, the slender stems 0-5(-8) cm, these and the firm pallid or glaucescent bifoliolate lvs thinly strigulose with appressed or narrowly ascending straight hairs up to 0.25-0.8 mm, the callous-margined lfts either glabrous ciliolate, or strigulose beneath only, or exceptionally strigulose on both faces, the scapose or cauline axillary erect 1-fld peduncles ± equalling the lvs or shortly exserted.

    Stipules erect firm linear-lanceolate (2-)3-10(- 12) x 0.4-0.9 mm, carinate dorsally by the prominent midrib, persistent.

    Lvs dimorphic, the earliest (not further described) commonly much shorter and their lfts broader than the rest, those associated with peduncles (1.5-)2.5-8(-10) cm; lf-stalk including discolored but otherwise undifferentiated pulvinus 6-32 x 0.4-0.6 mm, bluntly carinate dorsally, openly narrowly sulcate ventrally, shorter than their pair of lfts; gland between the lfts mostly reduced to a linear- subulate glabrous or puberulent stipe 0.2-1 mm, the head 0 or vestigial; lfts suberect from tip of lf-stalk subsessile, narrowly lance-acuminate or oblanceolate and then more abruptly acute and mucronate, either involute or conduplicate, 1-4.5(-5) x 0.2-0.5 cm, ± recurved distally, carinate dorsally by the midrib, smooth and veinless ventrally.

    Peduncles erect 2-7(-12) cm; bract ovate or lanceolate 1-3 mm, setulose-ciliolate persistent; pedicel 6-16(-21) mm; bud nodding, obovoid-ellipsoid obtuse strigulose or pilosulous; sepals pale green membranous-margined oblong-elliptic of subequal length 5.5-9.5 mm, becoming strongly 3-nerved and marcescent about base of pod; petals glabrous pale yellow drying stramineous or whitish dark- veined, subhomomorphic obovate- or oblong-elliptic-cuneate (5.5-)6.5-10 mm, equalling or slightly surpassing the sepals; androecium glabrous, functionally 7-merous, the linear-lanceolate staminodes 0.4-0.7 mm wide, the fertile stamens homomorphic except slightly accrescent toward distal side of fl, the filaments 1-2.2 mm, the anthers in profile narrowly lance-acuminate 2.9-4 x 0.6-0.8 mm, straight proximally, at or beyond middle strongly incurved and distally tapering into an obliquely terminal, shortly 2-lipped pore, the walls of thecae brownish- yellow laterally, paler yellow dorsoventrally and at apex; ovary strigulose or granular-puberulent; style filiform 2.3-3 x 0.1-0.2 mm, the stigmatic cavity symmetrically terminal; ovules 6-12.

    Pod declined sessile, plumply obovoid or oblong-obovoid (8-) 10-15 x 5-8 mm, a little laterally compressed but strongly turgid, the densely strigulose valves becoming papery brown, tardily dehiscent downward through both sutures, the cavity broadly septate; seeds turned with broad faces to the septa, in outline broadly paddle-shaped or compressed-pyriform 3.2-4.5 x 3-4.3 mm, the brown dull or sublustrous testa finely, sometimes obscurely rugulose, the transversely elliptic areole 0.5-0.7 x 0.8-1 mm; n = 14.—Collections: 34.

    Gravelly clay knolls, clay flats and playas in Larrea scrub and arid grassland, almost always on limestone, caliche or gypsum, 150-2000 m, local but locally plentiful over centr. and s.-w. Texas, from the headwaters of Brazos and Colorado rivers s. and s.-w. over Edwards Plateau to s.-e. trans-Pecos and the lower Rio Grande valley, thence sparingly s. around margin of Chihuahuan Desert to n. Durango, s. Coahuila and n.-w. Nuevo Leon.— Fl. III-VII and again, following summer rains, VIII-X.