Senna aristeguietae 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
Holotypus, NY (2 sheets); isotypi, MICH, U S.
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Description
Species Description - Diffusely bushy shrubs ±1.2-2 m with terete castaneous or livid hornotinous branchlets, pubescent with 4 sorts of trichomes, viscid-hispidulous nearly throughout with orange excretory setules ±0.2-0.3 mm, the stems and lf-stalks in addition minutely retrorse-puberulent with fine recumbent hairs ±0.2-0.4 mm, the lfts on both faces antrorsely pilosulous, and the stems, lf-stalks and valves of pod furthermore hispid with lustrous horizontal setae 0.8-1.8 mm, the foliage strongly bicolored, the membranous lfts when dry dull olivaceous-brownish or dark brown above, pallid beneath, the inflorescence of 2-5-fld umbelliform racemes axillary to coeval lvs, either immersed in foliage or shortly exserted. Stipules erect, linear-attenuate or flexuously setiform 5-8 mm, deciduous. Lvs 6-12.5 cm; petiole including livid pulvinus 8-16 mm, at middle 0.4-0.7 mm diam, rounded dorsally, narrowly or sometimes obscurely sulcate ventrally, ± twice as long as the first interfoliolar segment of rachis; rachis 4.5-9.5 cm; petiolar glands between proximal and often between the next 2-3 pairs of lfts, shortly stipitate, in profile 1-2.2 mm, the slenderly fusiform acute glabrous head 0.15-0.3 mm diam; lfts 8-11 pairs, ascending from rachis on livid pulvinule 0.6-1 mm, slightly accrescent upward, in outline oblong-obovate or oblong, obtuse mucronulate, the distal pair 12-24 x 5-10 mm, ±2.2-3 times as long as wide, all at base rounded-subcordate on proximal and broadly cuneate on distal side, the margin plane, the venation of upper face fully immersed, the slender centric midrib prominulous beneath, the 5-7 pairs of camptodrome secondary veins there faintly raised or almost imperceptible, the intervenium delicately reticulate by immersed but discolored veinlets. Peduncles 2-7 cm; bracts caducous, not seen; gland at base of pedicels 0; racemes 2-5-fld, the axis not over 1 mm; pedicels when 2 quasi-dichotomous, when 3-5 umbellate, at and after anthesis 21-30 mm, in fruit commonly bent beyond middle; fl-buds subglobose, densely puberulent and sometimes also setulose; sepals submembranous greenish or livid-tinged, obovate or oblong-obovate obtuse concave, the outermost 6-11 mm, the innermost 11-16 mm; petals yellow, puberulent dorsally along and between veins or glabrate, 4 broadly obovate narrowed to a slender claw, the cucullus broadly obliquely boomerang-shaped concave, nidulating the 2 long abaxial stamens, the longest petal 2.7-3.5 cm; filaments glabrous or minutely pilosulous, of 4 median stamens 1.4-2.3 mm, of the centric abaxial one 1.5-2.5 mm, of 2 latero-abaxial ones (5-)6-11 mm, the anthers of 4 median stamens including the short sublateral beak 5.5-7 mm, the beak dehiscent by 2 fully separated parallel slits, those of 3 abaxial ones more strongly incurved, their body 6-8 mm, abruptly contracted into an erect tubular 1-porose beak 2.6-4 mm; ovary densely white-setose and setulose; style filiform 5-7 mm, at incurved, sometimes slightly dilated apex 0.3-0.4 mm diam; ovules 20-26. Pod randomly spreading-declined, the stipe ±9 mm, the linear, piano-compressed, straight or slightly decurved body 8.5-11 x 0.75-0.8 cm, the papery pale brown valves scarcely elevated over seeds, becoming rather coarsely pallidly transverse-venulose and reticulate, the narrow interseminal septa ±4 mm apart; seeds not seen ripe, but a narrow areole evident on testa of immature ones.— Collections: 4.—Fig. 30.
Distribution and Ecology - Thickets and disturbed brush-woodland, near sea level in Venezuela and up to near 750 m in Brazil, the natural range enigmatic, collected once on the e. shore of Lago Maracaibo in Zulia, Venezuela, where possibly introduced, and twice in interior n.-w. and s.-centr. Minas Gerais (Virgem da Lapa; Rio Manso), Brazil.— Fl. in Venezuela X-XI, in Brazil III-VI.
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Discussion
This morphologically clearcut but otherwise contentious senna was first collected in Brazil by Auguste de Saint-Hilaire before 1822, about the turn of the turn of the century by Glaziou in south-central Minas Gerais (Rio Manso, ±20°20'S, 44°20'W), again in the northwest of the same state (between Virgem da Lapa and Barra de Salmas) in 1959 by Mendes Magalhaes, and in 1968 it inexplicably turned up in the Maracaibo Basin in northwestern Venezuela. It is a strongly characterized species, perhaps most closely related to the Brazilian S. acuruensis, of which it has the complex vesture of retrorse villi (on stems), an- trorse villi (on leaflets), viscid setules, and long non-secretory setae, but differs from all forms of it, as from all habitally similar Interglandulosae, in the elongate style. The shaggy-setose pistil and dorsally pubescent sepals distinguish it further from S. acuruensis sens, lat., of which the typical variety has more numerous (14-20, not 8-11) pairs of leaflets and the var. interjecta, similar in leaflet number, has substantially longer petioles. The seeds of S. acuruensis are narrowly oblanceolate in outline, whereas those of S. aristeguietae, not yet known fully ripe, appear to have the broad outline prevalent elsewhere in the series. Assuming that the Venezuelan plant is truly conspecific with the Brazilian ones, from which it differs only inconsequentially in length of sepals and longer filaments, we suppose that it was introduced in Zulia. A bicentric dispersal of this pattern is unprecedented and it is easier to look to eastern Brazil, the focus of speciation for viscid- setulose Interglandulosae, for a source of origin, than to Venezuela. The kindred Venezuelan species most like S. aristeguietae is S. saeri, found in the hill country of Lara at least 200 km east of Lago Maracaibo, which is instantly distinguished by fewer (4-6, not 8-11) pairs of larger, dorsally venulose leaflets, a narrower, more coarsely venose pod (4.5-6, not 7.5-8 mm wide), and a brachystylous ovary. Our choice of the Venezuelan plant as typus of what we believe will turn out to be a species endemic to Minas Gerais was dictated simply by the superior quality and relative completeness of the specimens at hand. The species is named in honor of our eminent Venezuelan colleague Leandro Aristeguieta.
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Distribution
Zulia Venezuela South America| Minas Gerais Brazil South America|