Senna spectabilis (DC.) 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
Typus infra sub var. spectabili indicatur.
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Synonyms
Cassia spectabilis DC.
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Description
Species Description - Amply leafy soft-woody trees of rapid growth, precociously flowering as bushy shrubs of rounded outline, at anthesis 2-15(-20) m tall, the trunk rarely attaining 25 cm diam, the stout hornotinous branchlets brown or fuscous pallid-lenticellate, the young growth except for sometimes glabrate upper face of lfts and dorsal face of sepals pilosulous throughout with fine spreading-ascending or partly (largely) straighter ascending or subappressed hairs up to 0.2-0.7(-0.9) mm, the foliage bicolored, the membranous lfts lustrous green above, paler dull beneath, the vesture of the inflorescence golden or tawny, of the foliage (variable in density) usually gray but sometimes at first lutescent, the inflorescence an ample thyrsiform panicle of racemes commonly leafy-bracteate proximally, then well exserted from foliage. Stipules caducous (lacking from many flowering and all fruiting spms), widely spreading and falcately incurved, the firm, narrowly linear-attenuate blades 4-10 x 0.2-0.9 mm. Major lvs (below and at base of inflorescence) 1.7-4(-4.5) dm; petiole including firm livid pulvinus 11-35(-40) mm, at middle (0.8-)l-2.5 mm diam, rounded dorsally, shallowly open-sulcate ventrally; rachis (10-)12-36 cm, the longer interfoliolar segments 10-28 (-30) mm; pulvinules 1.2-2.7(-3) mm; petiolar gland 0; lfts (8-)11-19(-20) pairs, decrescent toward both ends of rachis but more so proximally, the lowest pair often much smaller than the rest and readily deciduous, the largest beyond middle of rachis, these varying from ovate or elliptic obtuse mucronulate to narrowly ovate- or lance-acuminate (the acumen itself either obtuse or acute), the blade (2.6-)3-9.5 x (1-) 1.1-2.7(-3) cm, 1.9-4.3(-4.7) times as long as wide, at inequilateral base rounded or (when broad) shallowly cordate, the margin at least proximally re volute, the straight or gently incurved midrib, the (10-) 12-22 pairs of camptodrome and intercalary secondary veins and the reticular venulation all sharply prominulous beneath, somewhat less so or rarely almost immersed above. Racemes (6-)12-60-fld, the several simultaneously expanded or expanding fls raised to or beyond level of fl-buds, the axis including peduncle becoming (3-)4-20(-24) cm; bracts ovate acute or ovate- to lance-acuminate (1-)1.5-3.5(-4.5) mm, their broad base shielding the very young fl-bud but early caducous; pedicels at and after full anthesis (16-)20-32(-36) mm; fl-buds globose when young, usually puberulent at least proximally, sometimes glabrous, the sepals separating long before true anthesis of fl; sepals early reflexed concave, well graduated, the firm ovate outermost (2.5-)3-6 mm, the inner ones subpetaloid or marginally membranous, broadly obovate or suborbicular, the innermost (5.5-)6-10(-14) x 5-9.5 mm; petals rich yellow drying dull or brownish-yellow dark-veined, glabrous or rarely puberulent near claw, strongly heteromorphic, 4 similar in outline but of different lengths, broadly or narrowly obovate beyond the claw 13-36 mm, of these the vexillar one usually smallest and one abaxial (opposed to excentric pistil) longest, the fifth petal abaxial, coarsely thick-clawed, its blade turned at ±90° to the claw and folded over the androecium, measured along the curved midrib 22-38.5 mm; androecium functionally 7-merous, glabrous or exceptionally remotely pilosulous, the blades of 3 staminodes deeply cordate both at base and at apex (appearing 2-auriculate) 1.8-2.4 mm wide, the filaments all of equal length or slightly longer abaxially 1.5-3.5(-5) mm, the oblong pale yellow anthers of subequal length and except for beak isomorphic 4.5-7 x (1.6-)1.8-2.4(-2.6) mm, truncately rounded at both ends, straight or slightly decurved in proximal half, gently incurved distally, 8-sulcate lengthwise, the thecae of 4 median stamens and the centric abaxial one contracted into a very short divaricate lateral or shortly infraterminal beak separate to base and dehiscent by short vertical slit, those of 2 latero-abaxial stamens into scarcely longer but porrectly incurved, less clearly separated beaks; ovary glabrous or (locally in Colombia) thinly remotely pilosulous; ovules (72-)80-120, seldom all maturing into seeds; style scarcely differentiated from ovary externally, 1.5-2.5 mm, gently incurved distally and just below the conic tip (0.4-)0.5-0.7 mm diam, the minute terminal stigmatic cavity glabrous or ciliolate. Pod pendulous, the stipe 5-7 mm, the narrowly linear turgid, straight or nearly straight body 16-30 x 0.85-1.2(-1.3) cm, a trifle flattened along the broad sutures and a trifle compressed laterally, the cross section oblong-elliptic 7-10(-11) mm wide, the valves consisting of a) a thin succulent, early papery exocarp, b) a deeply corrugated woody mesocarp intruded between seeds as a complete partition, and c) a membranous endocarp less capacious than the cavity and free from the interior walls of the mesocarp, the narrowly oblong 1-seriate seed-locules defined by septa and endocarp 2-3.5(-4) mm wide, extending from suture to suture but separated on either side from the mesocarp by an empty cavity often as wide as themselves, the mature exocarp nigrescent, little or deeply depressed into the reentrant corrugations of the underlying mesocarp, irregularly rugulose but not venulose, splitting transversely along the thickened sutural margins, the whole valve finally dehiscent along the ventral suture and narrowly gaping to allow egress to the seeds; seeds turned with broad faces to the septa, broadly (narrowly) obovate in outline 4.8-6.8 x (3.3-)3.5-5.5 mm, compressed but moderately plump, the usually light orange-brown, sometimes fuscous or brown-olivaceous, exceptionally ochraceous testa dull or sublustrous, the oblong-elliptic or subrhombic areole (1.8-)2.1-3.3 x 1-2(-2.3) mm.
Variety Key - Key to the Varieties of S. spectabilis 1. Largest lfts of fully expanded lvs (4.5-)5-9.5 x ±1.5-2.5 cm, in outline narrowly ovate- to lance-acuminate, longer interfoliolar segments of rachis mostly 14-28 mm; widespread n. of Amazon valley, extending s. along e. foothills of Andes to Argentina, thence e into s - e. Bolivia and Paraguay. 202a. var. spectabilis (p. 603). 1. Largest lfts of fully expanded lvs (2.6-)3-5.5 x ±1-2 cm, in outline oblong-elliptic, elliptic or ovate, obtuse mucronulate; longest interfoliolar segments of rachis mostly 10-17 mm; e. Brazil (Piaui to Rio Grande do Norte, s.-e. Bahia, n.-centr. Minas Gerais and e.-centr. Goias). 202b. var. excels a (p. 604).
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Discussion
When Bentham admitted to his sect. Chamaefistula ser. Excelsae an eastern Brazilian Cassia excelsa and a circum-Caribbean C. spectabilis he established a tradition which, because of the discrete ranges of the pair, was not critically evaluated or challenged subsequently. Bentham found differential characters in number and shape of leaflets that coincided with varying depth of corrugation in the pod-valves. The corrugation of the pod is determined not, as in many sennas, by expression of the valve wall over the swelling seed, but by the unyielding woody endocarp which is in all Excelsae equally strangulated between the inter-seminal septa but becomes apparent externally only as the papery exocarp accommodates itself to the underlying mesocarpic armature. The degree of accommodation is quite variable, depending at least in part on maturity of the fruit when dried and perhaps in part on intrinsic differences in thickness of the exocarpic tissue. What is certain is that pods equally deeply corrugated are known to accompany all types of leaflet and are not limited to any one segment of the full range of the Excelsae. In a provisional separation of C. excelsa from C. spectabilis Isely (1975, p. 126) abandoned this character, but supposed the pedicels and pods of C. excelsa, as defined primarily by relatively numerous obtuse leaflets, to be on the average longer and its flowers more ample than those of C. spectabilis. There is an element of truth here, but we have found so wide an overlap in all measurements (see comparative data in our descriptions following) and such complete agreement in form of perianth and androecium and in structure of the pod that we can no longer recognize two discrete species. The best that can be said of the Brazilian populations which we here treat as var. excelsa is that they generally have two or three more pairs of generally smaller and more obtuse leaflets than var. spectabilis and flowers often but not consistently larger. Some specimens from Argentina that have been segregated as Cassia carnaval have leaflets in size and number like those of var. excelsa but in outline like those of var. spectabilis. Key to the Varieties of S. spectabilis 1. Largest lfts of fully expanded lvs (4.5-)5-9.5 x ±1.5-2.5 cm, in outline narrowly ovate- to lance-acuminate, longer interfoliolar segments of rachis mostly 14-28 mm; widespread n. of Amazon valley, extending s. along e. foothills of Andes to Argentina, thence e into s - e. Bolivia and Paraguay. 202a. var. spectabilis (p. 603). 1. Largest lfts of fully expanded lvs (2.6-)3-5.5 x ±1-2 cm, in outline oblong-elliptic, elliptic or ovate, obtuse mucronulate; longest interfoliolar segments of rachis mostly 10-17 mm; e. Brazil (Piaui to Rio Grande do Norte, s.-e. Bahia, n.-centr. Minas Gerais and e.-centr. Goias). 202b. var. excels a (p. 604).