Senna racemosa (Mill.) 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. racemosa indicatur.
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Synonyms
Cassia racemosa Mill.
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Description
Species Description - Round-headed subarborescent shrubs and trees of rapid growth with smooth gray trunks, at anthesis 3-10 m, the trunk sometimes reaching 3 dm diam but commonly much more slender, variably pilosulous or strigulose throughout or almost so with straight, forwardly subappressed or (more often) with some or all spreading or loosely ascending incurved or sinuous hairs up to 0.2-0.8 mm, the vesture of the foliage gray or when young golden, of the inflorescence golden or rusty, the lvs bicolored, dull or lustrous green above, paler beneath, the several or many pluriflorous racemes axillary to lvs crowded toward the tips of hornotinous branchlets and together forming a broadly round- or flat-topped, not or scarcely exserted corymbiform panicle. Stipules erect, subulate, linear- or lance-attenuate or linear-oblanceolate 2.5-9 mm, less than 1 mm wide, caducous. Lvs (7-)8-26 cm; petiole including firm, moderately dilated pulvinus 2-4.5 cm, at middle (0.7-)0.8-1.8 mm diam, subterete, very shallowly or obscurely sulcate ventrally, rachis (3-)3.5-17 cm; pulvinules 1-3.2 mm; lfts of larger lvs 4-12 pairs, moderately accrescent upward, the distal pair elliptic, elliptic-oblong, -obovate or broadly obovate, at apex deltately acute or obtuse to subemarginate and mucronulate, 2-6 x 0.9-2.4(-2.7) cm, 1.8-3.2 times as long as wide, at base when broad asymmetrically rounded-subcordate, when narrow broadly inequilaterally cuneate, the midrib and 5-9(-10) pairs of camptodrome (with occasional intercalary) secondary veins either immersed or finely prominulous above, commonly prominulous beneath, the tertiary venulation either expressed or invisible. Racemes densely 15-60(-120)-fld, the fl-buds in praefloration nodding and crowded into a blunt cone surrounded by several simultaneously expanded fls, the axis together with peduncle becoming 4-13(-20) cm; bracts firm, early spreading or reflexed, lance- or triangular-acuminate or -caudate 3-7 x 0.8-2.8 mm, deciduous at or soon after anthesis; pedicels 16-30 mm; fl-buds obovoid-subglo- bose, rusty-pilosulous when young but the inner sepals often glabrate marginally; sepals moderately or strongly graduated, obovate-suborbicular cymbiform, the outer ones 2.5-7 mm, the innermost 3.5-10 mm; petals rich dark yellow, usually glabrous dorsally beyond the puberulent claw, 4 subhomomorphic broadly obovate beyond the short slender claw, obtuse or emarginate, (9-) 10-16.5 mm, 1 abaxial strongly heteromorphic subsessile obliquely oblong as long or slightly longer than the rest (9-) 10-18 mm; staminodes glabrous, the small quadrate or cordate blade 0.8-1.2 mm wide; fertile stamens 7, homomorphic except slightly diminished abaxially, the filaments 1.2-2.5 mm, the oblong, slightly incurved or gently sigmoid glabrous or thinly weakly pilosulous anthers (2.6-)3-5.5 x 1.1-1.7, each theca 2-sulcate lengthwise, obtuse-subtruncate distally, the very small beaks lateral, opening by subparallel slits; ovary either glabrous or densely pilosulous; style 1.3-4 mm, gently incurved and slightly narrowed distally, 0.25-0.4 mm diam near the minute terminal stigma; ovules (16-) 18-28. Pod obliquely pendulous, the stipe 2.5-7 mm, the linear piano-compressed body straight or slightly arched downward, 8-19.5 x 1-1.6 cm, broadly flat-keeled by the sutures, the stiffly papery, reddish-brown or finally nigrescent valves prominently transverse-venulose, separating along both sutures, the seed-locules 4-10 mm long, as wide as the cavity; seeds transverse, compressed parallel to the valves, in outline oblong-obovate 4.4-7 x 2.6-4 mm, the testa beneath the cracking or flaking waxy outer integument pale fawn- or pinkish-brown smooth sublustrous, the areole linear or narrowly oblong-elliptic 1.4-3.6 x 0.5-0.9 mm.
Variety Key - Key to the Varieties of S. racemosa 1. Ovary and pod glabrous; mature lfts reticulately venulose on upper face; e. Mexico (s.-e. San Luis Potosi to Yucatan Peninsula), n.-e. Guatemala (Peten) and far w. Cuba; local in s.-w. Mexico (w. Michoacan and adjoining Colima). 2. Lfts 4-8 pairs, their blades subappressed-pubescent, the upper face only minutely puberulent or glabrate; pod 8-12 cm, the seed-locules relatively narrow, 4-6 mm long; Yucatan Peninsula (Campeche to Quintana Roo) and adjacent Guatemala, w. to n. Oaxaca; far e. Cuba. 196a. var. racemosa (p. 582). 2. Lfts of larger lvs 8-10 pairs; pod (unknown in s.-w. Mexican var. coalcomanica) 11-19.5 cm, the seed-locules 6-10 mm long; distantly allopatric. 3. Lfts densely softly pilosulous on both faces; local at ±1000-1400 m in valley of rio Moctezuma in s.-e. San Luis Potosi and closely adjoining Queretaro and Hidalgo. 196b. var. moctezumae (p. 583). 3. Lfts subappressed-strigulose; local near 140-500 m in w. Michoacan and adjoining Colima. 196c. var. coalcomanica (p. 584). 1. Ovary and pod densely rusty-pilosulous; pinnate venulation of lfts prominulous beneath only and tertiary venulation of both faces fully immersed; s. Mexico (s.-w. Mexico to Chiapas). 4. Lfts of larger lvs 9-12 pairs; s.-e. Mexico, Morelos and adjoining Guerrero. 196d. var. sororia (p. 584). 4. Lfts of larger lvs 6-9 pairs; e. Oaxaca and Chiapas. 196e. var. liebmannii (p. 585).
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Discussion
The ample material of Mexican Senna that has been referred in herbaria, either by Britton directly or by reference to Britton’s conspectus of Gaumerocassia (1930, p. 252), to Cassia liebmannii, C. ekmaniana and C. peralteana is essentially uniform in habit, inflorescence, flower-structure, pod and seed, and can readily and conveniently be accommodated within one species. Vicariant groups of populations differ between themselves in pubescence of foliage and ovary, in leaflet-number, in size of sepals, and in length of style and pod, but the differences are neither great nor absolute and fail to counterbalance the overall similarities. For this composite species we adopt the old epithet racem'osa, misapplied by Bentham to what is here called Senna silvestris and never hitherto satisfactorily identified. Within the species we can make out five varieties, neatly separated geographically but only weakly so morphologically. As redefined, S. racemosa has obvious close relations in S. andrieuxii, which see for comment, and S. peralteana, which is easily recognized by the reflexed stipular thorns of the mature stem and the highly asymmetric, narrowly racemose flowers. More numerous leaflets and a dehiscent pod not greatly thickened along the sutures separate S. racemosa from the partly sympatric S. atomaria. The dense corymbiform panicle of racemes, each of which bears simultaneously several expanded, deeply campanulate, rich yellow flowers elevated to or beyond the cone of nodding buds, combined with plurifoliolate glandless leaves and longitudinally sulcate anthers distinguish S. racemosa from all other Mexican and Central American sennas. Key to the Varieties of S. racemosa 1. Ovary and pod glabrous; mature lfts reticulately venulose on upper face; e. Mexico (s.-e. San Luis Potosi to Yucatan Peninsula), n.-e. Guatemala (Peten) and far w. Cuba; local in s.-w. Mexico (w. Michoacan and adjoining Colima). 2. Lfts 4-8 pairs, their blades subappressed-pubescent, the upper face only minutely puberulent or glabrate; pod 8-12 cm, the seed-locules relatively narrow, 4-6 mm long; Yucatan Peninsula (Campeche to Quintana Roo) and adjacent Guatemala, w. to n. Oaxaca; far e. Cuba. 196a. var. racemosa (p. 582). 2. Lfts of larger lvs 8-10 pairs; pod (unknown in s.-w. Mexican var. coalcomanica) 11-19.5 cm, the seed-locules 6-10 mm long; distantly allopatric. 3. Lfts densely softly pilosulous on both faces; local at ±1000-1400 m in valley of rio Moctezuma in s.-e. San Luis Potosi and closely adjoining Queretaro and Hidalgo. 196b. var. moctezumae (p. 583). 3. Lfts subappressed-strigulose; local near 140-500 m in w. Michoacan and adjoining Colima. 196c. var. coalcomanica (p. 584). 1. Ovary and pod densely rusty-pilosulous; pinnate venulation of lfts prominulous beneath only and tertiary venulation of both faces fully immersed; s. Mexico (s.-w. Mexico to Chiapas). 4. Lfts of larger lvs 9-12 pairs; s.-e. Mexico, Morelos and adjoining Guerrero. 196d. var. sororia (p. 584). 4. Lfts of larger lvs 6-9 pairs; e. Oaxaca and Chiapas. 196e. var. liebmannii (p. 585).