Cassia decumbens Benth.
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Authors
Howard S. Irwin, Rupert C. Barneby
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Authority
Irwin, Howard S. & Barneby, Rupert C. 1978. Monographic studies in Cassia (Leguminosae, Caesalpinioideae). III. Sections Absus and Grimaldia. Mem. New York Bot. Gard. 30: 1-300.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Holotypus, Pohl 2695, K (hb Benth.)! = IPA Neg. 1498 = NY Neg. 1050; isotypus, M = F Neg. 6232; isotypus, numbered Pohl 975, LE!
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Description
Species Description - Diffuse, weakly suffruticose herbs, either glabrous up to the viscid-setulose or -setose inflorescence or the stems beyond the middle, the lf-stalks with some stipules and Ift-margins sparsely setulose, the slender, smooth and subglutinous, often reddish stems humifusely radiating from the knotty xylopodium or (when short) weakly ascending, (1 -) 1.5-7 dm, simple or almost so, unilaterally leafy, the foliage concolorous, little dorsoventrally differentiated, the lfts glabrous on both faces, the terminal, solitary or few racemes incurved to vertical, usually far exserted. Stipules ascending, often falcate, linear or linear-setiform, (1-)1.5-6.5 mm, in age firm, persistent. Lvs incurved-ascending (2.5-)3.5-8.5 cm, slender-petioled; pulvinus little dilated, sometimes scarcely differentiated, often discolored, 0.8-1.4(-1.8) mm; petiole (6-)9-22(-26) mm, at middle 0.5-0.8(-0.9) mm diam, openly grooved ventrally; rachis (0.8-)1-4.4(-5.3) mm; lfts 2-6(-7), commonly 2-5 pairs, of subequal size or slightly diminished upward, tilted forward from rachis, turned half face to face, edgewise to the meridian, on softly dilated, when dry wrinkled pulvinule 0.4-1.1 (-1.3) mm, in outline broadly obovate to suborbicular or elliptic-obovate, emarginate or shallowly retuse, less often obtuse, exceptionally ovate-elliptic, muticous or minutely callous-mucronulate, (8-) 10-28 (-30) x (7-)8-23 mm, at base very oblique, on proximal side cuneately decurrent almost to the rachis, on distal side rounded to cordate, the margins either entire and glabrous to remotely gland- setulose or when setulose sometimes minutely crenulate, the blades rather stiffly chartaceous, on both sides dull olivaceous, glabrous, the slender centric midrib and 4-7(-8) pairs of major secondary nerves above immersed or rarely subimpressed, beneath delicately prominulous, the tertiary venulation usually imperceptible, or beneath rarely a trifle elevated, but not forming a regular reticulum. Inflorescence terminal to the primary stem and sometimes to 1-2 short distal branchlets, throughout viscid and hispid or hispidulous with yellow setae up to 0.5-2.5 mm, loosely and usually simply racemose, exceptionally weakly branched, the individual racemes (5-)12-45-fld, the axis (except of some depauperate ones) becoming (5-)7-25(-30) cm, the 1-3 fls simultaneously expanded elevated about to level of next succeeding buds; bracts spreading, narrowly ovate or lanceolate, (1 -)1.4-3.5(-4) mm, persistent; pedicels slender, strictly ascending, variable in length, those low on the raceme up to 2-6 cm, often some (chiefly sterile, or distal) shorter; bracteoles (0.5-)2-2.5 mm below calyx, resembling bracts, little smaller, persistent; buds ovoid, apiculate, thinly yellow-setose and sometimes minutely villosulous; sepals widely expanded at anthesis, subpetaloid, yellow tinged with reddish-brown or purple, the outer oblanceolate-elliptic, subacute, the inner broadly elliptic, obtuse, widely petaloid-margined, the longest 9-14.5 x 2.8-8 mm; petals yellow, widely ascending at anthesis, the four plane ones broadly obovate-flabellate, little graduated in size, the longest (15-) 16.5-22 x (12-)14-19 mm, the fifth shorter, falcately lance-oblong, coiled; ovary densely yellow- barbate-setose; ovules 5-9. Pod linear-oblong to oblong-elliptic in outline, straight or slightly arcuate downward, 3-5 (-5.5) x 0.65-0.95 cm, the glutinous, reddish-brown valves finely viscous-villosulous and yellow- setose; seeds (few seen) dark brown or almost black, plumply compressed-obovoid, scarcely lustrous, almost imperceptibly lineolate-pitted, 4.6-5 x 2.9-3.2 mm. - Collections: 28.
Distribution and Ecology - Rocky and sandy campo and cerrado, sometimes in disturbed ground, 975-1250 m, common locally in the Federal District (Brasilia, Sobradinho, Planaltina) and extending thence w. to Abadienia and s. to Cristalina in adjoining Goias. - Fl. IX-V.
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Discussion
Essentially herbaceous above the sometimes massive xylopodium, C. decumbens is closely related on one hand to C. benthamiana, vicariant immediately to the west, and on the other to the sympatric C. planaltoana. The former resembles C. decumbens in its diffuse habit, but differs in the densely viscid-pubescent stems and sessile or almost sessile leaves; the latter resembles it in the almost smooth or distally thin-setulose stems but is a more stiffly erect plant with, on the average, more numerous leaflets in the larger leaves, combined with shorter, glabrous sepals. Exceptions to these contrasts are mentioned in more detail under C. planaltoana.
The ample material of C. decumbens at our disposal reveals a certain degree of variation correlated with dispersal. The populations in Serra dos Cristais, whence comes the type, are characterized by 2-4 pairs of relatively large, suborbicular or subobcordate leaflets; the stems here are usually quite glabrous below the inflorescence, and the inflorescence itself is hispidly setose. In Distrito Federal the commonest form of C. decumbens has at least some larger leaves with 4-6 pairs of leaflets, which are on the average smaller, more variable in outline, and combined with stems often setulose above the middle, or with short-hispidulous inflorescence, or with both. Within single populations, however, there is some inconsistency in length and distribution of the pubescence (Irwin & at. 26603) as well as and independently of leaflet-number (3-6 pairs) in the largest leaves of a plant. We find no reliable criteria that would enable us to define varieties within the species.
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Distribution
Brazil South America| Goiás Brazil South America| Distrito Federal Brazil South America|