Senna tropica (Vell.) 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
Lectoholotypus, the cited plate.—Doubtfully equated by Vogel (1837, p. 20), and firmly but incorrectly so by Bentham (1871, p. 527), with C. laevigata (=our S. septemtrionalis).
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Synonyms
Cassia tropica Vell., Cassia loefgreniana Hoehne
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Description
Species Description - Shrubs and treelets at anthesis 1-3(-?) m, with green striate hornotinous and fuscous or atrocastaneous older leafless branchlets, resembling in habit and foliage S. septemtrionalis, glabrous except for residually puberulent pulvinules and sometimes remotely ciliolate lfts, the thin-textured foliage when dry dull brownish- or yellowish-olivaceous bicolored, paler beneath, some early racemes axillary and lateral, much surpassed by the associated lf, but most of them crowded into a subterminal leafy-bracteate corymbose panicle not or scarcely raised above the foliage. Stipules erect submembranous pallid or pale green lanceolate or oblanceolate 3-15 x 0.6-2 mm, caducous before maturity of associated lf, the lower ones scarcely known, all lacking from mature spms. Lvs (7.5-)9.5-21 cm; petiole including wrinkled pulvinus 3-6.5 cm, at middle 0.6-1.2 mm diam, angulately ribbed dorso-laterally, openly shallowly sulcate ventrally; rachis (1.2-) 1.5-7 cm, its longest (or only) interfoliolar segment 1.2-3.7 cm; glands between all pairs or all but the distal pair of lfts stipitate, in profile 1-2.5 mm tall, the ovoid acute or obtuse or lance-fusiform body 0.4-0.9 mm diam; lfts 2-4 pairs, only exceptionally in all lvs exactly 2, commonly either 2-3 or 3-4 pairs, accrescent distally, the distal pair broadly lance- or ovate-acuminate (4-)5-10.5 x (1.1-)1.3-3 cm, 3.1-4.7 times as long as wide, at base subequilaterally rounded or cuneate, the margin narrowly pallid-margined plane, the midrib cariniform beneath, immersed or depressed above, the (9-) 11-19 pairs of fine camptodrome with random intercalary secondary veins prominulous on both faces of mature blades, more strongly so beneath, an elaborate reticular venulation always prominulous beneath, often so above; the proximal pairs of lfts shorter and proportionately broad, mostly ovate and abruptly acuminate. Racemes shortly densely (5-)8-24-fld, the axis together with peduncle 2.5-7 cm, either shorter or a little longer than the subtending petiole; bracts pallid lance-subulate 1.2-2.8 x 0.3-0.6 mm, caducous before elongation of pedicel, this becoming at and after anthesis 12-22 mm; fl-buds plumply obovoid, except for minutely ciliolate sepals glabrous; sepals subpetaloid yellow commonly green- or fuscous-tinged, the outermost ovate or ovate-oblong (3.5-)4-5.5 mm, the innermost obovate or suborbicular 7-9 mm; petals of S. corymbosa, the emarginate vexillar one 10-14 mm; androecium glabrous, the blade of staminodes transversely reniform-obcordate 1.1-1.4 x 1.6-2 mm, the filaments of 4 median stamens 0.8-1.2 mm, of the sterile centric abaxial one 1.5-2 mm, of the 2 long abaxial ones dilated ribbonlike (5.5-)7-11 mm, the anthers of 4 median stamens plumply flaskshaped, including beak 3.2-4.5 x 1.1-1.6 mm, strangulated 0.6-0.9 mm short of apex and then expanded to the obliquely truncate apex 0.7-1.1 mm diam, the orifice dehiscent by U-shaped slit, the sterile abaxial anther 3.5-5 x 0.5-0.7 mm, the anthers of 2 long stamens lunately lanceolate in outline, including the beak (4.7-)5.2-7.4 x 1.2-1.5 mm, the beak itself 0.5-1 mm, its abaxial side prolonged into a bi-umbonate protuberance projecting 0.3-0.6 mm beyond the infraterminal orifice, this 2-porose; ovary glabrous or rarely puberulent at base; style gently incurved 1.5-3.7 mm, commonly somewhat swollen distally and 0.2-0.5 mm diam shortly below the minute stigmatic cavity; ovules (66-)74-96. Pod obliquely geotropic, the stipe 3-5 mm, the body cylindroid or obscurely obtusely quadrangular (5-)6-9 x ±1 cm, the seeds biseriate.—Collections: 41.
Distribution and Ecology - Thickets, disturbed woodland, rocky, sparsely wooded hillsides, sometimes surviving in hedges, below 600 m, local along the Atlantic foothills of s.-e. Brazil, from s.-w. Espirito Santo s.-w. through Rio de Janeiro and e. S. Paulo just into extreme n.-e. Parana (rio Pardo), weakly n. into s.-centr. Minas Gerais (Sa. do Cipo).—Fl. almost throughout the year.
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Discussion
Senna tropica is deceptively similar to S. septemtrionalis, that is to Cassia laevigata of Bentham’s revision or C. floribunda of some modem authors, in which it has lain concealed. It differs in its thinner-textured, more prominently and closely reticulate leaflets and most importantly in the structure of the two long anthers. In S. septemtrionalis the orifice of these anthers is either symmetrically truncate or, if obliquely so, then cut back from the abaxial to the adaxial side in the manner common in Senna, its posterior rim forming a diminutive scoop or pollen-cup. In S. tropica the slant of the orifice is reversed, its adaxial rim being produced in the form of a bluntly bi-umbonate nose, the biporose orifice itself becoming infraterminal, suggesting the underhung mouth of a shark or dogfish. As already noted, S. septemtrionalis, although encountered at scattered points in Andean Colombia and Peru and collected once in Brazil’s Federal District, is believed to be native only in cool montane Mexico and Central America, over 5000 km distant from the southeast Brazilian, lowland range of S. tropica. This discontinuity is of a pattern with that displayed by varieties of Senna hirsuta, of which endemic forms are sympatric with S. septemtrionalis and S. tropica in, respectively, Central America and Brazil; but these are linked by a series of forms intermediate at once in morphology and dispersal. In this revision we recognize as only varietally distinct S. pendula var. advena (=Cassia indecora), of which the principal differential character is a slightly modified beak to the long anthers. In these circumstances it will appear illogical to maintain S. tropica in the rank of species. Evaluated, however, in the context of its immediate relatives and neighbors S. araucarietorum, S. hilariana and S. corymbosa, which constitute a replacement series of vicariant small species extending from Rio de Janeiro to Paraguay and the Plate River in Argentina, S. tropica emerges as no less distinct than its peers. A devaluation in rank, evenhandedly applied to the group, would envelop all of them in a clumsy and unrealistic S. corymbosa. As pointed out in the diagnosis, S. araucarietorum, the immediate southern neighbor of S. tropica, is readily distinguished from it by the syndrome of leaves and symmetrically truncate anthers of S. septemtrionalis with the relatively few, uniseriate seeds of S. corymbosa.
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Distribution
Espirito Santo Brazil South America| Rio de Janeiro Brazil South America| São Paulo Brazil South America| Paraná Brazil South America| Minas Gerais Brazil South America|