Senna acuruensis (Benth.) 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 2: 455-918.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Typus infra sub var. acuruensi indicatur.
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Synonyms
Cassia acuruensis Benth.
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Description
Species Description - Profusely handsomely floriferous arborescent shrubs, at anthesis (1-)2-5 m, with densely leafy pliant annotinous branchlets, these with all lf-stalks and (commonly but not always) axes of inflorescence viscidulous with erect yellowish or orange tapering or capitate setules up to 0.2-0.4 mm mixed with minute incurved whitish villi and (rarely) in addition pilose with filiform spreading-ascending hairs to 1 mm, the foliage bicolored, the thinly chartaceous lfts dull dark brownish- olivaceous above, pallid beneath, varying (as described for the vars.) from glabrous to densely pilose on one or both faces, the inflorescence of simple racemes arising directly from axils of distal lvs and about as long or longer than them, sometimes by reduction of foliage distally becoming paniculate. Stipules erect setiform 3-8(-9) mm caducous. Lvs of primary stems (5-)6-15 cm (of some branchlets shorter, not further described), highly variable in number and size of lfts, these varying (acc. to var.) from 4 to 19(-20) pairs, when fewer larger; petiole including firm, moderately dilated pulvinus 9-30 mm, at middle 0.35-0.6 mm diam, shallowy sometimes obscurely sulcate ventrally; rachis 2-12.5 cm; petiolar glands between several proximal and often, but diminished upward, between all pairs of lfts, stipitate, the lower in profile 1-3 mm tall, the stipe nearly always puberulent, the glabrous discolored head slenderly ovoid-acuminate or claviform 0.2-0.45 mm diam; lfts ascending from rachis, face upward, on slender livid pulvinule 0.6-1.1 mm, in outline ovate-, obovate- or oblong-elliptic to broadly obovate or oblong-obovate, obtuse mucronulate or subemarginate (exceptionally incipiently deltate-acute), the largest of the larger lvs 1-3.7 x 0.4-1.8 cm, at base asymmetrically rounded, the straight centric midrib with (4-)5-7 pairs of camptodrome secondary veins usually all finely raised above, always so beneath, the midrib there cariniform, the tertiary and reticular venulation variable, above immersed, faint, or evident, beneath usually finely prominulous. Peduncles 2.5-5.5 cm; racemes (2-)3-9(-17)-fld, the fls either subequidistant or (when few) subumbellate or subverticillate, the axis 0.2-7 cm; bracts oblanceolate or obovate-elliptic concave 1.5-3 mm, nidulating the very young fl-buds, promptly caducous; pedicels 21-32 mm; buds subglobose obtuse, glabrous beyond immediate base or the outer sepals puberulent and ciliolate; sepals greenish or yellowish, often petaloid-margined, finely several-nerved from base, strongly unequal, the inner ± twice as long as outermost, broadly obovate-suborbicular (6-)6.5-11(-12) mm; petals golden-yellow, dorsally glabrous or at base puberulent along major veins, highly dissimilar in form, the 3 adaxial relatively small, long- clawed, oblance-obovate in outline, the 2 abaxial larger but dissimilar, one asymmetrically ovate-obovate-subcordate beyond the short claw, the opposed one obliquely reniform scoop-shaped subsessile, this nidulating 2 of the 3 beaked anthers; androecium glabrous, the filaments of 4 median stamens 1.5-3 mm, of one abaxial (1.5-)2-3 mm, of 2 abaxial 5.5-10.5 mm, the anthers of 4 median ones oblong little incurved 4-7 mm, with abruptly incurved beak ±0.5 mm dehiscent by parallel or almost confluent slits, those of 3 abaxial ones lunately incurved 6-8 mm, abruptly contracted into an erect tubular beak 3-4 mm, this slightly enlarged at apex and its orifice divided by a filiform septum; ovary glabrous, thinly ciliolate especially below middle or thinly pilosulous; style 1.8-3 mm, at apex 0.4-0.55 mm diam; ovules 38-50. Pod spreading or pendulous, the stipe 4.5-8 mm, deltately dilated into the valves, the narrowly oblong flat body 8-11 x 1.1-1.5 cm, the 3 sutural nerves all cordlike or the middle one narrowly winged, the plane papery nigrescent valves finely transverse-venulose, scarcely elevated over the seeds; seeds Unear-oblong in outline, obtusely 4-angular, 5.6-7 x 1.1-1.6 mm, the testa pale brown, sometimes faintly rugulose, marked on each face by a linear-elliptic areole 1.52.3 x 0.25-0.4 mm.
Variety Key - Key to the Varieties of S. acuruensis 1. Lvs at once shortly petiolate and plurifoliolate, the petiole 9-16-(-19) mm, the lfts relatively many and small, in larger lvs 14-19(-20) pairs, the amplest of them 10-18 x 4-8 mm; upland centr. Bahia to centr. Pernambuco. 164a. var. arcuruensis (p. 508). 1. Lvs at once relatively long-petiolate and paucifoliolate, the petiole 15-30 mm, the lfts fewerand larger, in larger lvs 4-13 pairs, the amplest of them 14-37 x 8-18 mm; e.-centr. and s.-e. Bahia. 2. Lfts 8-13 pairs; all axes of inflorescence densely viscid-setulose. 164b. var. interjecta (p. 508). 2. Lfts 4-7 pairs; axes of inflorescence glabrous or almost so, the pedicels sometimes residually setulose. 164c. var. catingae (p. 509).
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Discussion
The typus of Cassia acuruensis, the only example known to Bentham, was at once geographically and morphologically marginal to its species. In the light of modern collections it takes its due place in a series of Bahian sennas very constant in characters of flower and pod but extremely variable in size and number of leaflets and, largely independently of these, in quality and distribution of the mixed pilose and viscid-setular vesture. Until recently the typi of Cassia acuruensis, with 14-20 pairs of small leaflets pilose on both faces, and of C. catingae, with only 4-7 pairs of substantially larger glabrous ones, the latter further characterized by glabrate inflorescence, appeared safely and distantly distinct; but they are now united by numerous intermediate forms which we group here into three varietal categories, characterized primarily by leaflet number. These accord fairly well with dispersal patterns, the multifoliolate types being largely confined to Chapada Diamantina and those with fewer leaflets to the more eastern ranges and the coastal lowlands, but all coinciding in the lower and middle Contas valley where the essential unity of the species as redefined herein becomes especially evident. The species is very closely related to the northwardly vicariant S. trachypus and now no longer separable from it by number of leaflets although reliably distinct in the thickened, not winged sutures of the pod. In flowering condition only S. acuruensis var. catingae is likely to be confused with S. trachypus; its fully disjunct range and glabrescent axes of inflorescence then provide for rapid discrimination. Viscid-setular pubescence of stem and leaf-stalk, absence of stipitate glands at base of the pedicels and linear seeds enclosed in a broad pod together sharply distinguish both S. acuruensis and S. trachypus from all otherwise similar Brazilian Interglandulosae except the rare S. aristeguietae, different in the elongate style and pubescent sepals. Key to the Varieties of S. acuruensis 1. Lvs at once shortly petiolate and plurifoliolate, the petiole 9-16-(-19) mm, the lfts relatively many and small, in larger lvs 14-19(-20) pairs, the amplest of them 10-18 x 4-8 mm; upland centr. Bahia to centr. Pernambuco. 164a. var. arcuruensis (p. 508). 1. Lvs at once relatively long-petiolate and paucifoliolate, the petiole 15-30 mm, the lfts fewerand larger, in larger lvs 4-13 pairs, the amplest of them 14-37 x 8-18 mm; e.-centr. and s.-e. Bahia. 2. Lfts 8-13 pairs; all axes of inflorescence densely viscid-setulose. 164b. var. interjecta (p. 508). 2. Lfts 4-7 pairs; axes of inflorescence glabrous or almost so, the pedicels sometimes residually setulose. 164c. var. catingae (p. 509).