Senna cana (Nees & Mart.) 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. cana indicatur.
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Synonyms
Cassia cana Nees & Mart.
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Description
Species Description - Freely branched, densely leafy, potentially or actually arborescent shrubs at anthesis (1-)1.5-6 m, with ribbed or obtusangulate atrocastaneous or gray-fuscous hornotinous branchlets, except for often glabrescent fl-buds and inconspicuously hairy upper face of lfts villosulous or pilosulous throughout with fine incumbent, flexuous or crisped and entangled, whitish or rufescent hairs up to 0.1-0.5 mm sometimes mixed with random longer hairs, small thickened ones, or livid setae, the foliage conspicuously bicolored, the often firm-textured but sometimes membranous lfts glossy dark green above, whitish- or tawny-tomentulose or -pilosulous beneath, the inflorescence a panicle of racemes axillary to upwardly diminishing lvs, shortly or scarcely exserted from foliage. Stipules varying in form from erect and linear-attenuate to greatly dilated and auriculately amplexicaul, 3-12 mm long from point of attachment, the blades when dilated reflexed, either tardily deciduous or caducous before full expansion of lf. Lvs (below inflorescence) 5-15(-16.5) cm; petiole including the little differentiated pulvinus 4-18(-20) mm, at middle 0.8-2.3 mm diam, obscurely ribbed dorsally, narrowly margined ventrally; rachis 2.5-9.5(-ll) cm, each interfoliolar segment slightly dilated upward; glands nearly always lacking at first and often at distal pair but present between all the rest, stipitate or subsessile, in profile (0.8-) 1-3(-3.5) mm long, the glabrous or puberulent, ovoid, clavi- or fusiform acute or obtuse head 0.3-1.2(-l.4) mm diam; pulvinules moderately swollen, scarcely wrinkled 0.6-3 mm; lfts 3-8 pairs, ± accrescent distally but either the distal or the penultimate pair longest, these obliquely elliptic, ovate-elliptic, narrowly oblong-ovate or lance-elliptic, less often oblance-elliptic or narrowly obovate, obtuse mucronulate to deltately or truly acute, 2-6.5(-7) x (0.7-)0.8- 2.5(-2.7) cm, (1.7-)2.3-3.3(-3.8) times as long as wide, at base either inequilaterally cordate or cordate only proximally and cuneate distally, the margins strongly revolute, the straight or gently incurved midrib immersed or impressed above, cariniform beneath, the 5-12(-13) pairs of major (and rare random intercalary) secondary veins strongly raised beneath, anastomosing close to the margin, the tertiary venulation sometimes fully immersed, sometimes delicately but sharply raised on one or on both faces. Racemes (5-)7-25(-30)-fld, the fls at anthesis raised about to the level of unopened buds, the axis little elongating, together with the short peduncle becoming 2.5-11 (-13) cm; bracts firm or foliaceous, lanceolate or rarely ovate-acuminate, 3-12 x mm, either caducous or persisting through anthesis; mature pedicels (10-) 16-37 mm; young fl-buds subglobose glabrous or pilosulous, the early emergent inner sepals always glabrous dorsally but ciliolate; sepals strongly graduated, obovate obtuse concave, the inner subpetaloid, up to (-7)7.5-13(-17) mm; petals (of ser. Laxiflorae) golden-yellow, pilosulous dorsally, the longest 16-26 mm (caveat: corollas precociously expanded before true anthesis appear much shorter); androecium functionally 7-merous, the filaments usually and the grooves of the anthers sometimes pilosulous, the filaments of 4 median stamens 1.5-3(-3.5) mm, the centric abaxial one (2-)3-8(-11) mm, of 2 latero-abaxial ones dilated ribbonlike (3-)4-11(-13) mm, the anthers of 4 median (differentiated into unequal pairs) nearly straight 3-6.5(-8.5) mm, the divaricate biporose beak ±0.7-1.6 mm, the anthers of the centric abaxial one 6-8.5(-11) mm and of 2 latero-abaxial ones lunately incurved (8-)9- 13.5(- 15) mm, these contracted into a porrect scooplike beak (0.5-)0.7-1.1 mm, its orifice divided by a slender septum; ovary densely rusty-pilosulous; style straight, gradually attenuate distally, 5-8.5 mm, at symmetrically truncate stigma 0.2-0.35(-0.4) mm diam; ovules 20-32. Pod (poorly known) variously ascending-spreading, outwardly arcuate or almost straight, the stipe 3-6 mm, the narrowly linear body 9-15 x 0.4-0.55 cm, compressed-tetragonal, the accessory rib parallel and approximate to the ventral suture dilated into a narrow wing, the sutures commonly undulately strangulate between seeds, the interseminal septa marked externally by a shallow groove, the seed-locules 4-5.5 x 2.5-4 mm, obviously longer than wide; seeds basi-petally vertical, oblong-obovate in outline, compressed parallel to the valves, ±3.5-4 x 1.8-2.4 mm, the testa dull brown or dull purplish-brown, the elliptic areole 1-1.5 x 0.4-0.6 mm.
Variety Key - Key to the Varieties of S. cana 1. Vesture of the lower face of lfts tomentulose, composed of tightly crisped, ± matted hairs mostly 0.1-0.25 mm, commonly concealing the whole surface, the intervenium, however, sometimes more thinly hairy than the always pannose-tomentulose veins; upland interior and w. Bahia to adjac. e.-centr. Goias and n.-centr. and w.-centr. Minas Gerais. 2. Stipules ± dilated at base, the herbaceous blade reflexed and auriculate-amplexicaul, at point of attachment 1-7 mm wide, persistent into maturity of lf; lfts 4-8 pairs; valves of pod narrowly winged along each side of the ventral suture only, the seed-locules extending to the dorsal margin of the fruit; widely dispersed as above. 59a. var. cana (p. 229). 2. Stipules linear-setiform erect, at base less than 1 mm wide, early caducous; valves of pod narrowly winged along each side of both sutures, the seed-locules consequently extending to neither margin of the fruit; local on upper Rio Contas in Bahia. 59b. var. hypoleuca (p. 230). 1. Vesture of lower face of lfts pilosulous with loosely incumbent, weakly sinuous hairs up to 0.3-0.6 mm, or minutely sparsely strigulose, or quite glabrous; Atlantic slope of Chapada Diamantina s. through e. Minas Gerais to Rio Doce in Espirito Santo. 3. Lower face of leaflets incumbently pilosulous. 4. Bracts narrowly lance-acuminate or-caudate 4-8 x 1.4-2.8 mm, deciduous; relatively southern from Rio Pardo s.-ward. 59c. var. pilosula (p. 230). 4. Bracts foliaceous, ovate-acuminate (4-)6-12 x 2.5-4 mm, long persistent; locally abundant in Sa. do Sincora and vicinity, s. just into n.-e. Minas Gerais. 59d. var. phyllostegia (p. 231). 3. Lower face of leaflets glabrous or minutely sparsely appressed-strigulose; bracts early caducous; n. Sa. do Sincora and vicinity. 59e. var. calva (p. 232).
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Discussion
As defined in the foregoing description, S. cana is a polymorphic species, variable like its close ally S. velutina in form and duration of the stipules, but much more so in pubescence of the foliage, in flower size, and some other details. It differs from S. velutina and also from S. australis in the generally shorter or narrower leaflets, in the almost constant absence of a gland between the proximal pair of leaflets, in the more contracted, subcorymbose racemes of ordinarily smaller flowers and, so far as appears at present from scanty evidence, in the narrowly winged rather than merely ribbed valves of the pod. None of these differences is profound, and some large-flowered S. cana from the western margin of the species’ range, where it abuts on that of S. velutina, come close to bridging the gap. A case could be made on technical grounds for combining all members of ser. Laxiflorae into one megaspecies consisting of seven or eight geographic elements which, whatever taxonomic status may be thought appropriate, are most probably recent derivatives of a common ancestral stock. A still poorly understood lowland form of S. cana var. pilosula from Espfrito Santo closely simulates in its relatively broad leaflets S. australis native to nearby coastal restinga, and a firm distinction between var. pilosula and S. lechriosperma, or between var. pilosula and the unnamed senna from Chapada dos Veadeiros mentioned below, is unattainable if the pod (not certainly known as yet to be diagnostic) is lacking. Consequently, until much more can be learned about the fruits and seeds, which ripen tardily when few botanists are in the field, we propose to follow the most conservative policy consistent with the data available. The prime focus of interspecific variation in S. cana lies in the uplands of interior Bahia and north-central Minas Gerais, where the species, in whatever form it may take, is the only member of ser. Laxiflorae encountered. The most widespread variety, characterized by variably dilated stipules and tomentulose vesture, is var. cana, which ranges along both slopes of Chapada Diamantina from northern Bahia south into northern Sa. do Espinhaço in Minas Gerais, thence extending across the Sao Francisco valley, in Bahia to Espigao Mestre and immediately adjoining Goias and in Minas to the Paracatu-Paranaiba watershed. The very similar var. hypoleuca, identical in pubescence but different in the narrow caducous stipules, somewhat fewer and larger leaflets and a more emphatically four-winged pod, apparently replaces var. cana very locally on upper Rio de Contas. Along the Atlantic slope from Sa. do Sincora south to Rio Doce in Minas Gerais and adjoining Espirito Santo, S. cana is represented by a series of forms essentially identical to var. cana in habit, inflorescence and dilated stipules, but collectively different in the loosely pilosulous vesture of the leaves and stems. This series readily subdivides into a southern group, var. pilosula, ranging southward from Rio Pardo, with small deciduous bracts like those of var. cana or var. hypoleuca, and a northern var. phyllostegia, common in Sa. do Sincora but collected once in the northeastern corner of Minas Gerais, differing from all other forms of the species in broad foliaceous, relatively persistent bracts. The pods of the two last are unfortunately unknown and their status, possibly as a species distinct from tomentulose S. cana sens, strictior., may well require reevaluation.