Senna wislizeni (A.Gray) 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. wislizeni indicatur.
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Synonyms
Cassia wislizeni A.Gray
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Description
Species Description - Stiffly branched xeromorphic microphyllous and drought-deciduous, potentially arborescent shrubs at anthesis 1-5(-6) m, the branches of 3 sorts: a) pliant hornotinous long-shoots with developed internodes, floriferous at least distally; b, present in only some plants) shorter, stiffly divaricate branchlets lateral to long-shoots, usually floriferous, early leafless and functioning as thorns; and c) knotlike brachyblasts axillary to fallen primary lvs and consisting of a tuft of stipules and a fascicle of usually smaller lvs; old stems gray or castaneous, commonly lenticellate, the young stems, lf-stalks and inflorescence commonly strigulose with appressed or subappressed gray hairs to 0.15-0.45 mm or (locally) more densely pilosulous throughout with erect lustrous hairs to 0.3-0.5 mm (exceptionally few random setae to 1 mm), the firm subconcolorous lfts either olivaceous or pallidly subglaucescent, varying from glabrous on both faces to dorsally strigulose or pilosulous on both faces, the racemes of proportionately large showy fls arising mostly from axils of lvs on long-shoots, forming an open or contracted panicle, a few rarely in the dry season from leafless branchlets. Stipules erect, narrowly lanceolate or setiform (1-)2-7 mm, those of primary lvs often early caducous, those of fasciculate lvs subulate or acicular 0.7-3.5 mm, early dry but persistent. Primary lvs (0.9-)1.2-4.5(-5) cm; petiole including slender wrinkled pulvinus 2.5-11 mm, at middle 0.2-0.5 mm, narrowly sulcate; rachis (2.5-)4-25(-37) mm, the longer interfoliolar segments (1-)2-7 mm; gland 0; pulvinules 0.4-1 mm; lfts (2-)3-5(-6) pairs, little or not accrescent distally, broadly or narrowly obovate, obtuse mucronulate (aristulate) or shallowly emarginate, the distal pair 4-15 x 2.5-7.5 mm, 1.6-2.3 times as long as wide, semicordate or inequilaterally rounded at base, the margin plane, the venation above fully immersed or faintly raised, the midrib prominulous beneath either its whole length or only proximally, the (3-)4-6 pairs of camptodrome with rare intercalary secondary veins and sometimes tertiary connecting venules immersed or weakly raised above, either immersed and discolored or prominulous beneath; fasciculate lvs similar but mostly smaller, the lfts 2-4 pairs. Racemes loosely (2-)3-13(-17)-fld, 1-3 fls expanding on a given day, the axis together with peduncle becoming (0.5-)1-5(-7) cm, sometimes persistent and ultimately thorny; bracts subulate, narrowly lanceolate or ovate 1.5-3 mm caducous; pedicels 12-24(-26) mm; young fl-buds globose, glabrous, puberulent or rarely pilosulous; sepals yellowish, greenish or purplish-brown, strongly graduated, the smallest outermost one ovate or oblong-elliptic 3-5(-5.5) mm, the innermost amply obovate-suborbicular membranous-margined 6.5-10 x 5.5-8 mm; petals glabrous yellow, fading yellow brown-veined, conspicuously clawed, 4 oblong-obovate or -elliptic unequal, one abaxial one thick-clawed and highly asymmetric, its blade turned at ±90° to claw, either longer or shorter than the rest, the longest petal (caution: fls with expanded petals but immature androecium may be smaller) 16-28 mm; androecium glabrous, the 3 staminodes 1-1.8 mm wide, the filaments of 4 median stamens 0.9-2 mm, of 2 latero-abaxial ones 2-3.5 mm, of the centric abaxial one (4.5-)5.5-9 mm, the 7 fertile anthers of similar girth and except for direction of beak of similar outline, all gently incurved, the 4 median ones 4-6.2 x 1.4-2 mm, their divaricate beak 0.35-0.6 mm, the body of 3 abaxial anthers 4.8-6.2 x 1.7-2 mm, its porrectly incurved beak 0.7-1.5 mm, the fertile anthers all dehiscent by 2 short slits; ovary and style glabrous, the latter 0.7-2 x 0.2-0.4 mm, very slightly incurved distally, the minute stigmatic cavity terminal; ovules 22-40. Pods obliquely ascending and randomly declined from ascending pedicels, the stipe 5-8 mm, the linear piano-compressed straight or gently decurved body (7-)8-24 x 0.55-0.75(-0.8) cm, bicarinate by the cordlike sutures, the firmly papery or subcoriaceous dull or highly lustrous purplish-green or livid, finally brown or nigrescent valves becoming delicately transverse-reticulate, at maturity either plane or raised over each seed in the form of 1 or 2 transverse ridges, the inter- seminal septa thickened but very narrow, the locules 4-7.5 mm long, commonly as long or a little longer, rarely a little shorter than wide; seeds strongly compressed parallel to the valves, in outline rhombic, rhombic-paddle-shaped or almost square 4-5.5 x 3-4 mm, the brown or pinkish-brown testa smooth dull, the lustrous elliptic areole 0.6-1 x 0.3-0.7 mm.
Variety Key - Key to the Varieties of S. wislizeni 1. Stipules of primary lvs promptly caducous, usually before maturity of the associated lf; valves of pod dull when ripe, not raised over seeds or, if so, then only as a single low transverse ridge; secondary venulation of lower face of lfts not or obscurely prominulous; s. Mexico n. to the s. lobe of Chihuahuan Desert (to n. Zacatecas and s. Nuevo Leon), wholly s. of lat. 25°N.2. Body of pod 16-24 cm; ovules 31-40; thorny secondary branchlets often but not always present; s. Mexico in lat. 16-20°N (Colima to Puebla s. to Oaxaca). 193a. var. pringlei (p. 573). 2. Body of pod 9-15(-16) cm; ovules 25-32; no thorny secondary branchlets; s. Chihuahuan Desert in lat. 21-25°N (Queretaro to n. Zacatecas and s.-w. Nuevo Leon). 193b. var. painteri (p. 574). 1. Stipules of primary lvs more persistent, usually into or through maturity of the associated lf; valves of pod highly lustrous when ripe, elevated over each seed in the form of 2 transverse ridges, these sometimes joined at middle by a shorter vertical ridge; secondary venulation of lower face of lfts bluntly or sharply prominulous; centr. and n. Chihuahuan Desert n.-ward from lat. 25°N, extending feebly n.-w. into Sonora.3. Vesture of the whole plant appressed; desert n. from 27°N. 193c. var. wislizeni (p. 574). 3. Vesture of the whole plant pilosulous; Mapimi Depression in centr. Chihuahuan Desert in lat. 25-26°N (n.-w. Durango and adjoining Coahuila). 193d. var. villosa (p. 575).
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Discussion
In a study of Cassia for the Chihuahuan Desert Flora we developed (Irwin & Barneby, 1975, p. 16, fig. 2) a comprehensive concept of C. wislizeni that encompassed, as three vicariant varieties, three species of Britton’s genus Palmerocassia. We are now obliged to stretch the definition of the species a little further so as to accommodate Cassia pringlei, thought to differ decisively from C. wislizeni and all close allies in the long pod and in development of divaricate thorny branchlets lateral to annotinous long-shoots. These branchlets are, however, an uncertain feature of C. pringlei, striking when present but absent from some specimens, and the length of the pod, 16-24 cm when all 31-40 ovules develop successfully, is not decisively diagnostic, since the pod of other varieties, with 22-32 ovules, can reach a length of 16 cm. It should be emphasized that the calyx, the corolla, and the androecium, with its centric abaxial anther elevated beyond its neighbors on a long filament, remain essentially uniform and are exactly shared only by the closely related S. monozyx next following. In the context of its genus, which is of tropical mesophytic derivation, we suppose that the southern var. pringlei represents the primitive core of S. wislizeni sens. lat. from which the other varieties, as they moved north into progressively colder and drier climates, were derived by selection. The order of presentation follows this hypothesis. Key to the Varieties of S. wislizeni 1. Stipules of primary lvs promptly caducous, usually before maturity of the associated lf; valves of pod dull when ripe, not raised over seeds or, if so, then only as a single low transverse ridge; secondary venulation of lower face of lfts not or obscurely prominulous; s. Mexico n. to the s. lobe of Chihuahuan Desert (to n. Zacatecas and s. Nuevo Leon), wholly s. of lat. 25°N. 2. Body of pod 16-24 cm; ovules 31-40; thorny secondary branchlets often but not always present; s. Mexico in lat. 16-20°N (Colima to Puebla s. to Oaxaca). 193a. var. pringlei (p. 573). 2. Body of pod 9-15(-16) cm; ovules 25-32; no thorny secondary branchlets; s. Chihuahuan Desert in lat. 21-25°N (Queretaro to n. Zacatecas and s.-w. Nuevo Leon). 193b. var. painteri (p. 574). 1. Stipules of primary lvs more persistent, usually into or through maturity of the associated lf; valves of pod highly lustrous when ripe, elevated over each seed in the form of 2 transverse ridges, these sometimes joined at middle by a shorter vertical ridge; secondary venulation of lower face of lfts bluntly or sharply prominulous; centr. and n. Chihuahuan Desert n.-ward from lat. 25°N, extending feebly n.-w. into Sonora. 3. Vesture of the whole plant appressed; desert n. from 27°N. 193c. var. wislizeni (p. 574). 3. Vesture of the whole plant pilosulous; Mapimi Depression in centr. Chihuahuan Desert in lat. 25-26°N (n.-w. Durango and adjoining Coahuila). 193d. var. villosa (p. 575).