Senna quinquangulata (Rich.) 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 1: 1-454.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Typus infra sub var. quinquangulata indicatur.
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Synonyms
Cassia quinquangulata Rich.
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Description
Species Description - Shrubs, weak bushy treelets and sarmentose bush-ropes mostly (1-) 1.5-7, occasionally clambering into the forest canopy up to 25 m, the rope becoming 1-5 cm diam but the stems mostly much more slender, the annotinous branchlets either angulate or terete striate, variably puberulent, strigulose or pilosulous with fine incumbent, less often appressed or erect (with few subretrorse) hairs up to 0. l-0.4(-0.6) mm, the axes of inflorescence and calyx nearly always gray-puberulent, rarely velutinously pilosulous, the chartaceous lfts strongly bicolored, above lustrously dark- or brownish-olivaceous and either glabrous, puberulent along midrib or finely puberulent (pilosulous) overall, the inflorescence either simply narrowly thyrsiform or more broadly thyrsiform-paniculate, the lower racemes or flowering branchlets mostly leafy-braceteate, the lvs abruptly diminished upward, the upper racemes naked or subtended by vestigial lf-stalks. Stipules falcately linear-oblanceolate acute or acuminate (3-)4-10 x 0.5-2.5 mm, the blades green or yellow-green, when over 1 mm wide distinctly venulose, caducous and often absent from mature flowering and from almost all fruiting specimens. Lvs below inflorescence (8-)10-22(-27) cm; petiole including strongly differentiated, discolored but little swollen, finally wrinkled pulvinus (1.8-)2.2-5.5(-6.5) cm, at middle 0.8-2 mm diam, the wings defining the open shallow ventral sulcus narrow thick, scarcely dilated upward under the pulvinules; rachis (9-) 12-32(-40) mm, shorter than petiole; glands (caution: often gnawed) 1 between each pair, arising between or the lower from just above the pulvinules, lanceolate or ellipsoid 0.5-1.5(-l.8) mm diam, either sessile (when tongue- or horn-like) or stipitate (when lance- or claviform), straight or forwardly incurved, in profile (2-)3-6(-7) mm tall, or the proximal one rarely only 1.5-2 mm; pulvinules subcylindric wrinkled (2.5-)3-7 mm, obscurely carinate on anterior side by decurrent lft-blade; lfts of distal pair obliquely elliptic-, ovate-, broadly lance-elliptic- or rarely obovate- acuminate, the acumen varying from short obtuse mucronulate to attenuate acute, the whole blade (5-)6-16 x (2.5-)3-7.5(-8) cm, ±1.5-3 times as long as wide, at base on proximal side broadly cuneate to subcordate, on distal one commonly cuneate, the margins revolute and sometimes also undulate, the gently incurved midrib with (7-)8-13(-14) pairs of major camptodrome (and often some intercalary) secondary veins finely low-prominulous above, more distinctly raised beneath, the tertiary and reticular venulation likewise prominulous on both faces but often more pronounced above than beneath. Peduncles with raceme-axis (1-) 1.5-8(-10.5) cm; racemes (5-)8-21(-26)-fld; bracts obovate- to elliptic-oblanceolate or lanceolate 1.5-8 x 1-1.8 mm (rarely -3 mm wide but then <5 mm long), incurved over young buds before elongation of pedicel, either early caducous or persisting into anthesis; pedicels at and after anthesis (10-) 12-32 mm; buds globose but the sepals separated before true anthesis by the expansion of petals and androecium; sepals firm subherbaceous, usually densely, often subvelutinously gray-strigulose externally and puberulent within (rarely glabrate), not much graduated, all convexly ovate, oblong-ovate or suborbicular, always obtuse, the longest (4-)4.5-6.5(-7.5), very exceptionally -9 mm, externally nerveless or faintly 3-nerved; petals firm, biscuit- or darker orange-yellow, pubescent externally and at least near base also within, subhomomorphic except the adaxial one sometimes broader, oblong-obovate or oblanceolate beyond the short claw, (9-) 10-15(-17) mm, heavily 3-veined from claw, the veins externally prominent; androecium functionally 7-merous, the filaments puberulent, those of 4 median stamens 0.8-1.8(-2.5) mm, those of 3 abaxial ones (1.5-)2-3.5(-5) mm; anthers glabrous or more commonly either puberulent along the grooves or minutely pilosulous overall, those of 4 median stamens (4-)4.5-9 mm, truncate, with very short 2-porose beak standing at right-angles to the little- incurved body, those of 3 abaxial ones shorter, 3-5.5 mm, with beak hardly longer (-0.9 mm) but slightly more porrect; ovary densely silky-pilosulous or -strigulose, at anthesis incurved over androecium, the more thinly pubescent or glabrate style 2-4 mm, abruptly swollen at apex into a cobra-like head 0.9-2.8(-3) mm diam, the oblique cup-shaped stigmatic cavity 0.6-1.8 mm diam; ovules (112-) 122-196(-220). Pod pendulous short-stipitate, the stipe 2-4 mm, the narrowly subcylindric nearly straight body 11-33.5 x 0.9-2 cm, the firm, coarsely transverse-venulose valves turning brown or fawn-color, dehiscent along ventral suture to expose the seeds clothed in fetid black pulp; seeds (not well known) biseriate, turned broadside to the septa, broadly oblong or oblong-obovoid compressed, the testa smooth lustrous brown, sometimes broadly but faintly areolate.
Variety Key - Key to Varieties of S. quinquangulata 1. Pod 11-28.5 x 0.9-1.5 cm; seeds ±5 mm in greatest diam; petiolar glands nearly always between each pair of lfts, always so in Colombia; widespread from Mexico to s.-e. Brazil. 26a. var. quinquangulata (p. 155).1. 1. Pod 30-33 x 1.8-2 cm; seeds 8-10 x 6-8.5 mm; gland between proximal pair of lfts only; n.-w. Colombia. 26b. var. meizonoloba (p. 156).
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Discussion
Senna quinquangulata is the commonest and most frequently collected of that group of Bacillares collectively characterized by lustrous, marginally revolute leaflets, a gland between each (rarely between only the proximal) pair of leaflets, a thyrsoid-paniculate inflorescence arranged around a straight primary axis, and a pod lacking thickened margins to the sutures. In the lower Amazon valley, interior Guayana, the middle Orinoco basin and parts of northern Venezuela and Panama its range overlaps that of the related S. undulata, or perhaps more exactly interfingers with it, for the latter is apparently adapted in equatorial latitudes to more porous sandy soils supporting a savanna climax vegetation and extends northward beyond S. quinquangulata onto the karst limestones of Yucatan. In any case within their common range S. undulata is instantly recognized at anthesis by the enlarged floral bracts and little dilated style. The largely West Indian S. viminea and wholly West Indian S. nitida are fully allopatric, the first differing in its short pod and the latter in the loss of one or two of the abaxial set of stamens. The sometimes deceptively similar S. oxyphylla has a gland between the lower pair of leaflets only. As here delimited and as already, at least in some degree, known to Bentham, S. quinquangulata is variable in orientation, density and length of pubescence and in amplitude of the petals, although these only exceptionally and locally (e.g. Bahia, Harley et al. 17516, NY) surpass 15 mm in length. In middle Amazonia, especially around Manaus, it is represented by a race with the relatively small, strongly undulate leaflets of S. undulata, here considered taxonomically unimportant, and independently on upper Rio Branco in Terr. Roraima and in southern Mexico by forms with densely pilosulous upper branchlets and inflorescence. Hitherto S. quinquangulata has not been recognized from Central America or Mexico, the few collections known to Britton & Rose (1930) having been segregated as the local endemic species Chamaefistula falcinella, villosula and rekoi, separated from each other by impalpable and moreover essentially unquantified states of pubescence and leaflet-shape and nowhere contrasted with South American S. quinquangulata. Schery (l.c., sub Cassia unica) suggested that Ch. falcinella, known only from the holotypus, might represent an individual variant of S. undulata in which the bracts had failed, as it were, to become enlarged and persistent; but several modern collections of good S. quinquangulata from Panama have rendered this hypothesis superfluous. The type-collection of Ch. villosula, from an outlying station in Jalisco, is at first sight remarkable for its dense velutinous-pilosulous branchlets (suggesting South Brazilian S. angulata) combined with unusually ample sepals (to 7 mm). It is matched precisely only by one collection from Coalcoman, Guerrero (Hinton 12547, K, NY) but both are certainly conspecific in the narrowest sense with a second gathering from Guerrero (near Petatlan, Langlasse 645, K) in which the same broad sepals coincide with a thin short but loose pubescence easily matched in Amazonian S. quinquangulata. Nearly identical to the last mentioned is a plant collected somewhere in Mexico by Beechey (K), which Bentham never identified, and by the holotypus of Ch. rekoi from Oaxaca. The typus of Ch. collinsii, amplified by a mature fruiting topotypus (Gregg 1014, MO), appears identical with some northern South American S. quinquangulata. A remarkable specimen from Surinam (Lely Mts., 550-710 m, 24.IX. 1975, Lindeman, Stoffers et al. 311, NY), with leaflets and dilated style of S. quinquangulata, but a hornlike gland between the proximal pair of leaflets only, globose flower-buds opening just before true anthesis, and very broad and big inner sepals (to ±10 mm), suggests a hybrid between S. quinquangulata and S. latifolia. Found on ferro-bauxite formations, this plant may perhaps, nevertheless, emerge as representative of a distinct, ecologically differentiated taxon. A specimen from Santa Maria Magdalena in eastern Rio de Janeiro (E. Pereira 1249, RB) has everything of S. quinquangulata except the distal petiolar gland and is provisionally interpreted as a minor variant. lf correctly named, this collection establishes an unexpected range-extension southward from Bahia and the population from which it came deserves particular study in the field. A few specimens from humid forest in northwestern Colombia, like the last in lack of the second petiolar gland, have with foliage and flower of S. quinquangulata immense pods and massive seeds unmatched elsewhere in the species; these seem sufficiently modified to require taxonomic status.