Senna septemtrionalis

Racemes (3-)4-10(-13)-fld, the expanded fls raised to level of the obliquely obovoid fl-buds, the axis together with peduncle becoming (1.5-)2.5-8 cm; bracts submembranous pallid, linear, lanceolate or subulate (1.5-)2-4.5 x 0.4-1 mm, caducous as pedicel begins to elongate; mature pedicels (12-) 15-25 mm; sepals either yellowish-green- or reddish-brown-tinged or sometimes bright yellow petaloid, well graduated, the outermost relatively firm ovate-elliptic 4-6.5 mm, the submembranous innermost one oblong-obovate or suborbicular 6.5-10 mm; petals bright yellow drying stramineous brown-veined, all short-clawed glabrous, the amply obovate or obovate-flabellate vexillar one ± deeply emarginate, the rest all obovate obtuse or the 2 abaxial ones narrower, all 5 of subequal length or the vexillar sometimes largest, the longest petal (12-) 13-16 mm; blade of staminodes obovate or suborbicular (1.7-)2-2.6 x 1.4-2.5 mm; filaments of 4 median stamens 1.3-2.2 mm, of the centric abaxial one 2-4 mm, of the 2 long latero-abaxial ones dilated ribbonlike (7-)7.5-10.5 mm, the anthers of 4 median stamens oblong-flaskshaped, including the short dilated, obliquely truncate beak 3.6-4.5 x 1.2-1.5 mm, that of the centric abaxial stamen 4.5-5.5 x 1-1.5 mm, either distinctly or scarcely narrower than its 2 long neighbors, these lunately lanceolate, yellow or brown yellow-tipped 5.5-7.5 x (1.1-) 1.3-1.8 mm, obscurely constricted 0.4-0.6 mm below the horizontally truncate apex, the orifice 0.6-1 mm wide, the rim 2- umbonate on the adaxial side, dilated abaxially into a small pollen-cup beyond the twin pores of the locules; ovary glabrous; style stoutly linear (2.6-)3-4(-4.3) mm, often a trifle dilated distally, not or scarcely incurved and just below apex 0.3-0.45 mm diam, often persistent into maturity of pod, the stigmatic orifice minutely ciliolate; ovules 62-80.

Pod obliquely ascending on stiff pedicel, the stipe 2.5-5 mm, the straight or obscurely incurved, cylindric or obtusely subquadrangular body when fully fertile 6-9.5(-10.5) x 0.8-1.1 (if strongly flattened in press becoming -1.3 cm wide), the smooth green or anthocyanic valves becoming pale brown, fuscous or ultimately black, paler-margined along the sutures, when fully ripe papery and faintly corrugated over the seeds, the moderately pulpy cavity divided into 2 parallel rows of locules, these when fertile becoming 1.7-2.6 mm long, occupying the breadth but only half the thickness of the cavity; seeds turned with broader faces to the septa, plumply compressed-obovoid (3.6-)3.8-4.9 x (2.7-)2.9-4 mm, ± emphatically pinched at hilum, the olive-drab or brown testa smooth or sometimes microscopically pitted, commonly lustrous but sometimes dull, exareolate; n =14.—Collections: 93.

Originally a shrub or treelet of sunny microhabitats in cool or moist oak, oak- pine and mixed pine-liquidambar forest, secondarily a prolific shrubby weed of old pastures, abandoned orchards, waysides and other disturbed or ruderal places, for over 200 years cultivated for ornament and since pre-Columbian times for folk medicine, the primary range of dispersal thereby modified and lost to view, but apparently truly native in Mexico at ±1000-1950 m along or near the crest and Gulf Slope of Sa. Madre Oriental from s.-e. San Luis Potosi to n. Oaxaca and Veracruz, and from the highlands of w. and s. Oaxaca and Chiapas s.-e. through montane Guatemala, Honduras and Nicaragua just into Costa Rica, in Mexico extending w. at scattered points along the Transverse Volcanic Range into Michoacan; naturalized since XVIII century on Jamaica and apparently more recently in hill country of centr. Puerto Rico and centr. Dominican Republic, reported (but surely only weedy or cultivated) from Martinique, Barbados and Gulf of Panama; collected infrequently and without data as to status but improbably wild in upland Colombia, Pacific Peru, the Federal District in Brazil, and from gardens in Argentina and Chile; long established in tropical Africa, India, Sri Lanka, Malay Peninsula, in Java and Sumatra (where it has acquired several vernacular names listed by De Wit, l.c. sub C. floribunda), in e. Australia and on some Pacific islands including Fiji and Hawaii; widespread in tropical and subtropical horticulture and under glass northward.—Fl. in tropical N. America mostly V-XI, but erratically on through the dry winter months, the long-persistent pods often contemporaneous with new fls, releasing their seeds by decay and weathering.—Retama (Mexico); frijolillo, moco (Guatemala); hedionda macho (Pto. Rico); arsenic-bush, Dooley weed, laburnum (Australia).

Senna septemtrionalis is the widespread circumtropical weedy senna with ovate-acuminate, basally equilateral glabrous leaflets and cylindric multiovulate pods that was long known as Cassia laevigata but since 1955 has usurped the epithet floribunda properly reserved for its hybrid progeny with S. multiglandulosa. Within a decade of its publication the basionym Cassia septemtrionalis was recognized by Colladon, and therefore by DeCandolle, as a prior synonym of C. laevigata Willd, and deliberately passed over as inappropriate in meaning, but this does not constitute a valid objection either by present rule or past convention. Zuccagni’s choice of the epithet northern indeed makes little sense unless, as seems probable, he had it from Sesse & Mocino, who already had a Cassia septentrionalis described in manuscript although only posthumously published many years later (see synonymy above). From the viewpoint of the Valley of Mexico a local senna might well appear relatively northern, the bulk of the genus being tropical or subtropical in dispersal. But this is by the way; the correct epithet is implicit in the synonymy given by Bentham (1871, p. 527).

Our concept of S. septemtrionalis is somewhat more narrowly defined than Bentham’s of Cassia laevigata. We consider genuine S. septemtrionalis to be native only in the northern hemisphere and probably only in highland Mexico and Central America; and we interpret the habitally similar southeast Brazilian sennas as the distinct species S. tropica and S. araucarietorum, which see for differential comment.

The spelling septemtrionalis, although much rarer than septentrionalis, is a variant encountered in classical antiquity and there is no reason to think that it was used other than intentionally by Viviani.