Senna andrieuxii

  • Title

    Senna andrieuxii

  • Author(s)

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna andrieuxii (Benth.) H.S.Irwin & Barneby

  • Description

    197.  Senna andrieuxii (Bentham) Irwin & Barneby, comb. nov. Cassia andrieuxii Bentham, Trans. Linn. Soc. London 27: 548. 1870.-"Mexico [more precisely "in ditione Puebla"], Andrieux, [PI. Mex.] n. 414, Bates."- Holotypus, Andrieux 414, G! isotypi, FI, K (originally numbered 177) = NY Neg. 1419, M, P, W!-Gaumerocassia andrieuxii (Bentham) Britton ex Britton & Rose, N. Amer. Fl. 23(4): 252. 1930.

    Cassia fulva T. S. Brandegee, Zoe 5: 233. 1906.-'‘Collected at El Riego, near Tehuacan, Puebla. [C. A. Purpus] No. 1195."-Holotypus, collected VI. 1905 (fl, old fr), UCJ isotypi, GH, MO, NY!-Correctly equated with C. andrieuxii by Macbride, Contrib. Gray Herb. n. ser. 59: 27. 1919.

    Cassia andrieuxii sensu Standley, 1922, p. 410.

    Shrubs and treelets 1-3.5 m, the leafless annotinous and older branchlets stiffly tortuous brown glabrate, the soft, densely leafy hornotinous ones with foliage and axes of inflorescence densely softly pubescent throughout with weak flexuous or simply spreading-incurved hairs up to 0.7-1.2 mm, the vesture (dry) strikingly bicolored, on lower face of lfts white- or gray-lanate, elsewhere golden-, brown- or rufous-pilosulous, the short subcorymbose racemes axillary or pseudoterminal to young branchlets, shortly or not exserted.

    Stipules linear-subulate 1-4.5 mm, densely lanulose caducous.

    Lvs (3-)4-14.5 cm; petiole 1-3.5 cm, at middle 0.6-1 mm diam, its very narrow ventral sulcus obscured by vesture; rachis 1.5-6(-7) cm; petiolar gland 0; lfts 3-5 pairs, moderately accrescent upward, the distal pair broadly obovate obtuse or emarginate 2-4.3 x 1.1-2.8 cm, 1.6-2 times as long as wide, inequilaterally rounded at base, the margin strongly revolute, the stout midrib with 5-7 pairs of secondary and ultimately an open mesh of tertiary venules all finely engraved on upper face, sharply prominulous beneath, the proximal lfts shorter and proportionately wider, sometimes orbicular.

    Peduncles 1-4.5 cm; racemes closely, at first subcorymbosely ±20-35-fld, the several simultaneously expanded fls raised to or beyond level of the crowded nodding lanate-pubescent buds, the axis little elongating, up to 3(-5) cm long in fruit; bracts lance-elliptic cymbiform 2-7 x 1.5-2 mm, tardily deciduous; pedicels 12-23 mm; sepals moderately graduated ovate-obovate obtuse, the firmer outer ones 4-6 mm, the membranous-margined inner ones 6.5-8 mm; petals rich yellow, pilosulous dorsally near claw and along midrib, when dry brownish-yellow coarsely dark-venulose, the vexillary one, 2 lateral and 1 abaxial all broadly obovate emarginate similar in shape, the first sometimes a trifle shorter than the rest 8.5-11 mm, one abaxial heteromorphic, thickly short-clawed, the oblong- spatulate limb turned at ±90° to claw, the whole petal longest of all and 11.5-15 mm; androecium functionally 7-merous, the 3 staminodes 2.5-3.5 mm, their spatulate limb 0.5-0.8 mm wide, the 7 fertile stamens subhomomorphic in shape but dwindling in size very gradually toward abaxial side of fl, their filaments stout glabrous 1.6-2 mm, the anthers oblong often slightly enlarged upward, truncately rounded at both ends, 2.3-4.2 x 1.4-1.7 mm, scarcely or not incurved, thinly pilose, the minute beaks infraterminal scarcely 0.2 mm long dehiscent by parallel slits; ovary lanate; style glabrous subulate 2-3 mm, gently incurved and tapering distally, just below minute terminal stigmatic cavity 0.3-0.4 mm diam; ovules 14-18.

    Pod broadly linear piano-compressed 7-13 x 1-1.3 cm, the valves when ripe papery fuscous densely rusty-pilosulous, the seminal locules ±5-8 mm long, as wide as the pod’s cavity; seeds transverse, obovate-paddle-shaped, compressed parallel to the valves, 6-7.5 x 4-5.5 mm, the testa light brown dull smooth, ultimately crackled, the elliptic areole 1.5-2.2 x 0.6-0.7 mm.-Collections: 14.

    Dry hillsides in matorral or disturbed oak-woodland, 1250-1850 m, commonly on limestone, locally plentiful on the sources of rio Papaloapan in s. Puebla and adjoining Oaxaca, Mexico, thence extending s.-w. in mun. Huajuapan to the margin of the Balsas basin.-Fl. VI-X(-XI).

    Senna andrieuxii appears to be a xeromorphic derivative of S. racemosa adapted to the severe climate of the Tehuacan Desert and cognate calcicolous thorn- forest of northern Oaxaca. Its compact known area of dispersal fits into the wide interrupted one of S. racemosa as neatly as a piece missing from a puzzle, and it seems likely to be, in reality, a member of the replacement series described under the latter. However that may be, the prevailingly small leaves, simplified down to five, four or three pairs of leaflets, numbers significantly less than found in vicariant varieties of S. racemosa, combine with the dense woolly indumentum, gray above and golden beneath, to establish a distinctive facies. With some reluctance therefore we maintain S. andrieuxii as specifically distinct.