Senna affinis

  • Title

    Senna affinis

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

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

  • Description

    12.  Senna affinis (Bentham) Irwin & Barneby, comb. nov. Cassia affinis Bentham in Martius, Fl. Bras. 15(2): 98. 1870.—. . in provincia Rio de Janeiro, ut videtur frequens, a collectoribus perpluribus lecta, e. gr. a Schuch de Capanema, Peckolt, Glaziou 1033., Luschnath . . .; in provincia Minas Geraes: Langsdorff, Sello, Claussen, Ackermann, Warming . . Lectoholotypus, Peckolt 221, collected III.1859 (fl), BR (hb. Mart., with dissections by R. L. Steyaert)! paratypi, Schuch s.n., BR, M! Glaziou 1033, BR! Langsdorff s.n., BR! Sello s.n., K (labelled C. puberulae affinis’)! = IPA Neg. 896 = NY Neg. 1441; F (fragm ex B)! Claussen s.n., K! Warming 212, F!

    Cassia sepium Martius ex Bentham in Martius, Fl. Bras. 15(2): 99. 1870, in obs., nom. nud.— ". . . e sepibus ad S. Joao del Rey et Camapuam, prov. Minas Geraes, a cl. Martio lecta . . —Spm. authent., Martius s.n., dated Apr. 1818, M! = F Neg. 6257.

    Cassia affinis sensu Bentham, 1871, p. 520.

    Weak shrubs and treelets at anthesis 1-4 m, in habit, stature, foliage and form of inflorescence essentially similar to remotely allopatric C. fruticosa but differing in minor details of the androecium and definitively in the pod and seeds, the young branchlets either sharply or obscurely 4-angular and like the foliage and axes of inflorescence variably strigulose-pilosulous with forwardly incumbent, less often straight subappressed or flexuously erect hairs up to 0.15-0.3(-0.5) mm, the foliage bicolored, the membranous lfts above dull or sublustrously olivaceous and minutely puberulent or rarely glabrous, beneath paler and always densely pubescent, the solitary racemes commonly all subtended by ample lvs but some, at least in late anthesis, often forming a shortly exserted leafless panicle, the primary axis in age flexuous or abruptly zigzag.

    Stipules caducous (little known), linear-setiform or very narrowly linear-oblanceolate straight or incurved ±5-8 x 0.25-0.6 mm, absent from many flowering and all fruiting spms.

    Lvs (disregarding obviously reduced distal ones) 11-34 cm; petiole including pulvinus (2.5-)3-8.5 cm, at middle 1.2-2.8 mm diam, prominently 5-ribbed, the shallow open ventral groove dilated toward the petiolar gland; rachis 1.5-5 cm, a little shorter than petiole; gland 1 sessile or less often shortly stipitate between proximal pair of lfts, including stipe 1.5-3.5 mm tall, the body varying from plumply ovoid or ovoid-pyramidal to narrowly fusiform (0.6-)0.8-2.5 mm diam glabrous; pulvinules (2-)2.5-4.5(-5) mm; distal pair of lfts obliquely ovate- or obovate-elliptic, usually shortly acuminate but either obtusely or acutely so, (8-) 10-21 x 4-9 cm, (1.6-) 1.8-2.5 times as long as wide, the base, venation and reticulation as in C. fruticosa, but the reticulation of dorsal face quite variable, the ultimate areoles sharply defined on dorsal face ±0.2-1 mm diam.

    Racemes (4-)8-25-fld, the axis including peduncle becoming 1.5-10 cm; bracts early dry deciduous at or before anthesis ovate, narrowly triangular or lanceolate (1-)1.5-3.5 mm; pedicels at and after full anthesis (13-) 16-30(-35) mm; young buds globose, glabrous above very base or thinly pilosulous overall; sepals variable in outline and in relative size, the outer sometimes almost as long as inner, sometimes only half as long, all oblong or obovate, concave, always obtuse, the longest inner one 5.5-10.5 mm, at first submembranous and faintly or obsoletely venulose, yellowish-green or red-tinged, becoming dry and rather prominently 3-6 nerved; petals of ser. Bacillares, the longest one 12-20 mm; functional stamens 7, the filaments glabrous or puberulent, all filiform (not thickened distally), those of 4 median ones 1.4-2.6 mm, those of 3 abaxial ones 2.5-4(-5.5) mm; anthers glabrous or almost so, those of 4 median stamens slightly incurved (4.3-)4.6-7.5(-8) mm, with divaricate 2-porose beak 0.3-0.55 mm, those of 3 abaxial ones (4-)5.5-10.5(-12) mm, with more strongly incurved body contracted into a porrect, also 2-porose beak 0.8-1.6 mm; ovary densely strigulose; style little dilated upward, 0.55-0.95 mm diam just below incurved stigma, the ciliolate cavity 0.5-0.8 mm diam; ovules 188-212.

    Pod pendulous, stipitate, the stipe 4-6 mm, the cylindric, straight or decurved body 14-24 x 0.7-0.9(-1) cm, the sutures ±1.5 mm wide, without thickened border, the valves almost imperceptibly strangulated at the transverse septa between seeds; seeds 2-seriate, turned broadside to septa, plumply narrowly obovoid- ellipsoid 4-5.1 x 2-2.4 mm, the testa lustrously atropurpureous, smooth or shallowly pitted, exareolate.—Collections: 69.

    Virgin and disturbed or second-growth woodland, 5-850 m, scattered along the coastal plain and Atlantic slope of s.-e. Brazil from e.-centr. Bahia to w. Rio de Janeiro (lat. 14-23°S), sparingly inland to the headwaters of Rio Doce and upper Sao Francisco valley (Felixlandia; Sa. do Cabral) in s.-e. and centr. Minas Gerais.—Fl. (I-)II-IV.

    Within its relatively restricted range of dispersal S. affinis is the one member of ser. Bacillares in which a single petiolar gland coincides with small flowers (petals mostly 12-18, rarely 20 mm), obtuse sepals, and moderately dimorphic stamens. In the coastal forest of Bahia its range overlaps that of similarly small- flowered S. quinquangulata, readily distinguished at all stages of growth by the gland between the distal pair of leaflets and at anthesis by the greatly dilated style; and also that of the very rare and poorly known S. acutisepala which appears to differ decisively in its subsymmetrical leaflets and pointed flower-buds. In general appearance S. affinis most closely resembles the primarily Mexican S. fruticosa, but differs in the terete filaments of the four median stamens, the uniporose beak of the abaxial anthers, the much more numerous (over 180, not 78-102) ovules, the narrower pod (7-10, not 10-18 mm diam), and the somewhat shorter, much narrower exareolate seeds. The sometimes deceptively similar S. bacillaris, thought by Bentham to occur in Rio de Janeiro but to be expected there only in gardens, has plane-margined leaflets, prevailingly longer petals (2-3, not 1.2-2 cm), and differentiated margins to the pod’s valves, while the androecium and areolate seeds more closely resemble those of S. fruticosa.

    As defined herein S. affinis is quite variable in details of vesture, reticulation of leaflets, shape and size of sepals, and degree to which the upper leaves that subtend the always solitary racemes are reduced in size or ultimately suppressed; in fact hardly two populations seem exactly simlar in all these features. In forest understorey the leaflets tend to be relatively large, thin-textured and more laxly reticulate than in more exposed or sunny sites; Sellow’s collection, provisionally describd by Vogel (1837, p. 15) as "C. puberulae affinis" and cited by Bentham in the protologue, is of this nature. The calyx varies independently in relative proportions and in outline of the sepals, of which the outer may be nearly as long or only half as long as the innermost and either oblong-oblanceolate or obovate. A remarkable variant (Irwin et al. 27187) from an outlying station on Sa. do Cabral in the Sao Francisco valley of central Minas Gerais has relatively enormous and heteromorphic stamens, the anthers of the long abaxial ones reaching a length of 8.5-10.5 (as opposed to a usual range of 5-8) mm. Another variant (B. Gates s.n. from Sta. Maria Magdalena in e. Rio de Janeiro, NY) is notable for its relatively narrow, lance-ovate leaflets, narrow sepals, and small, exceptionally slender anthers. The corresponding pods are still lacking.