Monographs Details: Senna x floribunda (Cav.) H.S.Irwin & Barneby
Authors:Howard S. Irwin, Rupert C. Barneby
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.
Synonyms:Cassia floribunda Cav., Chamaefistula floribunda (Cav.) G.Don, Cassia grandiflora Desf., Cassia corymbosa var. plurijuga Benth., Cassia herbertiana Lindl., Chamaefistula herbertiana (Lindl.) G.Don, Chamaefistula floribunda var. herbertiana (Lindl.) Vogel, Cassia hybrida Ten., Senna septemtrionalis (Viv.) H.S.Irwin & Barneby, Cassia laevigata Willd., Adipera arsenei Britton & Rose, Adipera bicolor Britton & Rose
Description:Species Description - Habitally similar to S. septemtrionalis, but the lfts (at least when young), pedicels and base of ovary finely pilosulous with weak incurved or subappressed hairs up to 0.2-0.7 mm, the inflorescence often corymbose-paniculate and ± exserted from foliage. Lvs (7-)9-16(-18) cm, the petiole 18-34 mm, the rachis (2.5-)3-8(-9.5) cm, its longest interfoliolar segment 12-25 mm; lfts 4-5 pairs, the distal pair lance- or oblong-elliptic, abruptly acute or acuminulate 3-7 x 1-2 cm, 2.5-4(-4.2) times as long as wide, at base inequilateral, rounded or subcordate on proximal and cuneate on distal side, the 8-14 pairs of secondary veins not or scarcely visible above, the tertiary venulation scarcely prominulous beneath. Racemes 4-15(-20)-fld, their axis with peduncle (2-)3.5-12 cm; vexillar petal 14-23 mm; ovary puberulent; ovules 50-64. Pod like that of S. septemtrionalis externally, the body (5-)6-7.5 x 0.7-0.9 cm, terete or somewhat laterally compressed, the seed-locules varying from irregularly 2- to strictly 1-seriate, the orientation of the seeds ± haphazard, some turned with broad faces to the septa, others obliquely to the valves.—Collections: 20.

Distribution and Ecology - Open rocky and disturbed habitats, sometimes on pedregal, ±1800-2300 m, primarily with or near the parent spp., but fully fertile and forming independent populations, local around the s. and s.-e. margins of the Mexican Plateau from n.-w. Michoacan to Puebla, n. to s.-e. San Luis Potosi, cultivated in Spain about 1800 and thence diffused in horticulture; reports from Durango, Barbados and elsewhere outside the common range of the parent species are from cultivated or weedy stock.—Fl. in Mexico mostly VI-X.

Discussion:The two first monographers of Cassia sens, lat., Colladon in consultation with his professor A. P. DeCandolle (1816) and Vogel (1837), agreed in recognizing the two species C. laevigata and C. floribunda, obviously close relatives but seemingly different in outline of leaflets, in pubescence, in incidence of petiolar glands, in architecture of the inflorescence, or in some combination of of these characters. Both species were then known principally from specimens cultivated in Europe; indeed, except for the Mexican type-collection of C. elegans H.B.K., there were no exact data about dispersal in the wild state. By 1870-1871 Bentham had evidence that C. laevigata, characterized by broadly and subsymmetrically lance- or ovate-acuminate, truly glabrous leaflets, was an American senna widely dispersed as a circumtropical weed; but C. floribunda, differing in its oblong- elliptic, basally inequilateral, variably pubescent leaflets and corymbose-paniculate rather than largely lateral racemes, remained a horticultural oddity which Bentham provisionally interpreted as a plurifoliolate variety of C. corymbosa. Here the matter rested until De Wit (1955, l.c.) summarily equated C. floribunda with C. laevigata and, following the dictates of priority, adopted the earlier epithet floribunda. Under this name De Wit really described and discussed only genuine C. laevigata, but since his synonymy has become generally accepted the genuine C. floribunda has dropped out of sight. The fact remains that there is a senna distinct from C. laevigata that grows wild in Mexico and answers excellently to the plant grown at Madrid in the first decade of the XIX century and independently described by Gomez Ortega as Cassia corymbosa (not of Lamarck) and by Cavanilles as C. floribunda. It is, however, found only in the common range of C. laevigata (=our Senna septemtrionalis) and S. multiglandulosa, at least sometimes in close association with both. Moreover it is morphologically intermediate in outline and pubescence of the leaflets, in the ovule-number, and in the arrangement of the seeds, which are strictly 2-seriate in S. septemtrionalis, stricly 1-seriate in S. multiglandulosa, but vary from 1-seriate to irregularly displaced in what we here call S. x floribunda. Localities where these three sennas are known to grow close together are on the peripheral foothills of Valle de Mexico (numerous collections), around Zitacuaro and Temascaltepec in Mexico State (Hinton 6216, 8278, 13546), and along the San Luis Potosi-Rio Verde highway near Santa Catarina (septemtrionalis: Roe & Roe 2160, Schubert & Souza 1919; multiglandulosa: Lasseigne 4887; × floribunda: Lasseigne 4886, 4889, Hill & Funk 1784). We feel convinced that Cassia floribunda is a fertile, self-perpetuating hybrid that probably was synthesized several times as opportunity arose for exchange of pollen between the parent species, features of which it incorporates in varying degree. The typus of Adipera bicolor, for example, has the relatively small elliptic, basally asymmetric leaflets of S. multiglandulosa, but they are glabrous or almost so. In the typus of A. arsenei the leaflets are larger and densely pubescent, in fact resembling those of the original C. floribunda which also came from Puebla. Different strains of the hybrid differ in flower-size, the handsome plant known in gardens as Cassia herbertiana representing the large-flowered extreme.
Distribution:Michoacán Mexico North America| Puebla Mexico North America| San Luis Potosí Mexico North America| Durango Mexico North America| Barbados South America|