Senna wurdackii 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
Holotypus, NY; isotypi, F, US.
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Description
Species Description - Shrubs and treelets at anthesis 2-6 m, with terete brown subglabrous, abruptly flexuous branchlets, the lf-stalks and dorsal face of lfts pilosulous with fine spreading-incurved hairs up to 0.2-0.4 mm, the chartaceous foliage strikingly bicolored, the lfts (dry) lustrously brownish-olivaceous above, pale and brown- nerved beneath, the thinly strigulous few-fld racemes both axillary and by reduction of uppermost lvs depauperately cymose-paniculate, mostly immersed in foliage. Stipules erect, falcately linear-oblanceolate acute, prominently venulose, 5-8 x 0.6-1 mm, deciduous before the lf. Lvs mostly 10-14 cm; petiole including little dilated pulvinus 20-28 mm, at middle 0.8-1.3 mm diam, openly shallow-sulcate ventrally; rachis 12-21 mm, shorter than petiole; glands between proximal or (commonly) between both pairs of lfts, sessile or shortly stipitate, including stipe 2.6-3 mm long, the ellipsoid or lance-ellipsoid glabrous body 0.5-0.8 mm diam; pulvinules 3-4 mm, distal pair of lfts subsymmetrically lance-elliptic, almost imperceptibly acuminate, at very apex obtuse, 6-9.5 x 2-3.2 cm, ±3 times as long as wide, at base inequilaterally cuneate, the almost straight and centric midrib with 7-9 pairs of major camptodrome secondary and few connecting tertiary veins all immersed above, prominulous beneath, the subsequent reticulation faint; proximal pair similar, ±2/3 as long, proportionately only a trifle broader. Racemes solitary, shortly 3-12-fld, the axis including peduncle 1.5-4 cm, bracts ovate acute 2.5-3 mm, persistent into anthesis; pedicels 20-28 mm; fl-buds globose, glabrous; sepals subpetaloid, faintly veined, little graduated, broadly obovate or oblong-obovate, the innermost 8.5-11 mm; petals (of ser. Bacillares) up to 17-22 mm, the vexillary one broadest; functional androecium 6-merous, glabrous, the filaments of 4 median stamens thickened 2-2.5 mm, those of 2 abaxial linear but thickened at apex ±3.5 mm, the anthers of 4 median stamens differentiated into slightly unequal pairs, oblong slightly incurved 5.5-9 mm with abruptly divaricate beak 0.3-0.4 mm, those of 2 abaxial ones lance-ovoid 2.5-3.7 mm with nearly erect 2-porose beak 1.2-1.5 mm; ovary densely gray-strigulose; style scarcely or not dilated, ±0.8 mm diam just below stigma, the orifice ±0.25 mm diam; ovules ±120. Pod not seen fully formed, apparently like that of S. oxyphylla, up to 2 dm long; seeds unknown.—Collections: 5.—Fig. 16.
Distribution and Ecology - About granite outcrops in savanna, local, known only from the banks of middle Orinoco River and tributaries between 5°30' and 7°N in s.-w. Estado Bolivar and adjoining Apure and Territorio Amazonas, Venezuela, and on the Colombian bank in the n.-e. corner of Vichada.—Fl. VI, X-XII.
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Discussion
The flora of the cerros and associated savannas of that segment of the Orinoco valley that separates Venezuela from Colombia has an endemic element to which the Cassieae contribute taxa from two sections of genus Chamaecrista: C. (Xerocalyx) desvauxii var. triumviralis Irwin & Barneby; C. (Chamaecrista) glandulosa var. rapidarum Irwin & Barneby and var. crystallina Irwin & Barneby; and the senna described here as S. wurdackii. All of these represent groups widely dispersed over the Neotropical region in patterns so diffuse and generalized as to provide little evidence of origins. The close affinity of S. wurdackii, except in a general way to all smaller-leaved Bacillares, is difficult to assess. The plant is notable for the syndrome of narrow bracts and stipules, mostly biglandular leaf-stalks, relatively small elliptic, strongly bicolored leaflets with re volute margins, ample glabrous sepals and an androecium peculiar for the loss of one of the three abaxial stamens. In the last character it resembles the West Indian S. nitida and the north Colombian S. smithiana, but differs from both in the subsymmetrically elliptic leaflets pilosulous on the dorsal face. The perhaps equally related S. rupununiensis from the eastern margin of the Guayana Highland resembles S. wurdackii in size and outline of leaflets, but these are strongly venulose on the upper face, merely strigulose beneath, and associated with the heptamerous functional androecium normal in ser. Bacillares. Fruits and seeds of the more local members of the series are so little known that comparisons are not yet possible. We take pleasure in dedicating S. wurdackii to Dr. John J. Wurdack, Smithsonian Institution, a member of the first New York Botanical Garden expedition and leader of the second that encountered the species in modern times. It was collected first sometime in the XIX century by the French traveller Chauffenon (P).
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Distribution
Bolívar Venezuela South America| Apure Venezuela South America| Amazonas Venezuela South America| Vichada Colombia South America|