Senna aversiflora

  • Title

    Senna aversiflora

  • Author(s)

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna aversiflora (Herb.) H.S.Irwin & Barneby

  • Description

    176.  Senna aversiflora (Herbert) Irwin & Barneby, comb. nov. Cassia aversiflora Herbert in Sims, Curtis’s Bot. Mag. 53: t. 2638. 1826.-. . raised at Spofforth [Dean Herbert’s home in Yorkshire, England] . . . from Brazilian seed."-No typus known to survive, but the protologue decisive.

    Cassia aversiflora sensu Vogel, 1837, p. 43 (the name wrongly attributed to W. J. Hooker). C. biflora var. rostrata sensu Bentham, 1870, p. 121, ex parte (quoad pl. Blanchet. e Jacobina et Martianam hirtam in Obs. 1 notatam), non C. rostrata Mart. sens. str.

    Cassia aversifolia Britton & Rose, N. Amer. Fl. 23(4): 259 (lapsu). 1930.

    Erect shrubs of bushy outline, reportedly sometimes arborescent, closely resembling S. rostrata in habit, with virgate, obtusely angulate-ribbed hornotinous branches either sparsely or densely hispid with fine lustrous, horizontally spreading setae up to (2-)3.5-7 mm and in addition charged with random minute thickened livid trichomes, the lf-stalks, some lft-margins and ovary furthermore minutely white-strigulose, the setae sometimes very sparse or confined to the base of some branchlets or to the stipule-margins, the foliage glaucescent bicolored, paler beneath.

    Stipules flexuously incurved-ascending, linear-attenuate 4-11 x 0.2-0.5 mm, 1-nerved, caducous.

    Lvs 5-9.5 cm, slender-petioled; petiole including moderately dilated livid pulvinus (13-) 15-28 mm, at middle 0.45-0.8 mm diam, 3-ribbed latero-dorsally and sulcate between the ribs, openly sulcate ventrally; rachis 2.5-4.5 cm; petiolar gland between proximal pair of lfts sessile or shortly stipitate 2-4 mm, the reddish body elliptic- or semi-obovate obtuse or acute glabrous, strongly compressed, in profile (0.8-) 1-1.4 mm wide; rarely a smaller gland at second pair; lfts (4-)5-8 pairs, by day ascending from rachis, turned half face to face on linear livid pulvinule 1-1.4 mm, in sleep sharply tilted backward, strongly accrescent distally, in outline obovate to broadly oblanceolate obtuse or shallowly emarginate, the distal pair 15-28 x 4.5-12 mm, (2-)2.2-3.4 times as long as wide, all at base asymmetrically rounded to broadly cuneate or (when broad) subcordate, the margin plane, the slender centric midrib immersed on upper and prominulous on lower face, the 4-7 pairs of major camptodrome secondary veins very slender, sometimes finely raised beneath, the tertiary venulation imperceptible.

    Racemes numerous axillary to young lvs, capitately 2-fld, the peduncles 1.5-3.7 cm, the quasi-dichotomous pedicels 1.8-3 cm, in fruit bent shortly below hypanthium; bracts varying from lanceolate to linear-oblanceolate 1.5-2.5 mm, caducous; a gland sessile beside base of each pedicel; buds either globose or angulate by distinctly keeled outer sepals, glabrous or almost so; sepals submembraneous, fuscous with pale or petaloid margins, strongly graduated but all broadly obovate-suborbicular obtuse, the large inner ones 7-10 mm; petals yellow, externally puberulent along (and often between) the major veins, heteromorphic, 3 adaxial and 1 (larger) abaxial obovate or oblong-obovate from a narrowly cuneate claw, the fifth (abaxial) largest, very obliquely semi-obovate or reniform sessile or almost so, concave and nidulating the long stamens 21-34 mm; androecium usually glabrous, the thecae rarely setose in the lateral grooves, the filaments of 4 median anthers 1.4-2.6 mm, on both or at least on one side of the fl united at base, those of 2 abaxial ones 3-4 mm, of 1 (lateral) abaxial 4.5-6 mm, the thecae of 4 median stamens oblong slightly incurved 4-5 mm, the divaricate subterminal beak ±0.5 mm opening by one U-shaped slit, those of 3 abaxial ones more strongly incurved, the body 4.4-6.5 mm abruptly contracted into an erect tubular beak 2.4-3.8 mm, opening by a single, ±2-lipped pore; ovary strigulose; style 1-1.8 mm, at incurved tip 0.3-0.4 mm diam; ovules 26-52.

    Pod erratically oriented, the stipe 6-10 mm, the narrowly linear straight or slightly curved body 9.5-16.5 x 0.45-0.55 cm, the brownish-nigrescent, thinly strigulose valves expressed over each seed in the form of a 4-ribbed pyramid almost as long as wide, the distance between interseminal septa 3.3-4 mm; seeds (few seen truly ripe) compressed-rhomboid, ±3.2 mm diam, the testa dull blackish, the areole elliptic ±1 x 0.4 mm.-Collections: 21.-Fig. 32.

    Caatinga thickets, ±80-700, on Chapada Diamantina up to 1000 m, apparently local in the taboleiro hill-country of n. and e.-centr. Bahia from Rio Paraguagçu w. to Sa. Agurua, n.-e. interruptedly to e. Pernambuco (Tapera; Pau D’Alho) and Paraiba (Areia).-Fl. irregularly through the year.

    Senna aversiflora was not distinguished from S. rostrata by Bentham, who treated the Brazilian Interglandulosae with twin-flowered racemes as a single variety of S. pallida (see next following). At a time when only a few incomplete and mostly cultivated specimens were available for comparison this was hardly surprising, but the now substantial material accumulated from the eastern Brazilian states is found to fall into two perfectly distinct series, treated herein as species independent both of each other and of S. pallida. Differences between them in pubescence, androecium, pod and seed have been brought out in our key to ser. Interglandulosae (couplet 18/18, q.v.). In the context of this series, as indeed in Senna as a whole, the lustrous setose cauline pubescence of S. aversiflora, which recalls the multifoliolate S. mutisiana and S. williamsii, is a precarious differential character; it is in fact sometimes reduced to a rudiment concentrated on the stipules. Rare calvescent plants of S. aversiflora, among them the specific typus, are deceptively similar at anthesis to S. rostrata. But the longer and narrower pod, with valves elevated over each square or broadly quadrilateral seed-locule into a decussately folded pyramid, is decisively different.

    The epithet aversiflora, as explained by Dean Herbert, referred to the "singular manner in which the pair of flowers appear to shrink from each other, by the incurvation of the petals that come in contact." It incorporates the earliest known mention of enantiostyly in Senna.