Senna ruiziana (G.Don) 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.

Family

Caesalpiniaceae

Scientific Name

Senna ruiziana (G.Don) H.S.Irwin & Barneby

Type

Typus infra sub var. ruiziana indicatur.

Synonyms

Chamaefistula ruiziana G.Don

Description

Species Description - Amply leafy subarborescent shrubs and small trees, at anthesis 3-15 m, with terete striate brown, commonly glabrous or subglabrous, less often (var.) pilosulous stems and branchlets, the lower face of the thinly chartaceous lfts with axes of inflorescence strigulose-pilosulous, usually with forwardly impressed or incumbent, less often with erect hairs up to 0.1-0.5 mm, the foliage bicolored, the lf-blades lustrous green above, paler subglaucescent beneath, the inflorescence usually a greatly contracted leafless panicle of racemes (sometimes simplified to a single raceme) arising from 1 or more serial supra-axillary buds associated either with mature living lvs or on old wood, then sometimes clustered on a knotty burl, the whole very much shorter than the lvs, rarely some flowering axes developed and bearing lf and fl simultaneously. Stipules (caducous, little known) falcately oblanceolate or linear-oblanceolate acute, 4.5-10 x 0.8-3 mm, prominently venulose. Lvs (2-)2.5-4 dm; petiole including discolored but little swollen pulvinus 2.5-6 cm, at middle (1.5-) 1.7-2.9 mm diam, obtusely ribbed both laterally and ventrally so as to appear ventrally 3-sulcate; rachis 2.5-6(-7) cm, a little longer or shorter than the petiole; gland 1 sessile or almost so between the proximal pair, lanceolate or ovate in outline, 2.5-4 mm tall; seta glandular-thickened, appearing as a second gland behind the distal pair of pulvinules, these 6-11 (-13) mm; distal pair of lfts obliquely obovate-short-acuminate 15-28 x 6-12.5 cm, ±2-2.7 times as long as wide, at base very asymmetrically cuneate on both sides, sometimes (especially on proximal side) broadly so or subcordate, the margins narrowly revolute, the forwardly incurved midrib with (9-) 10-14 major (with few random intercalary) secondary veins above immersed or barely prominulous, beneath sharply cariniform, the tertiary venules and fine reticulation subequally prominulous on both faces or subimmersed above, the ultimate defined areoles <1 mm diam; proximal pair of lfts 1/2-2/3 as long as the distal, proportionately broader and usually broadest below middle, hence obliquely ovate. Axis of panicle 0-2(-3) cm, on older stems often reduced to a woody knot; axis of individual (6-)10-45-fld racemes with peduncle 2-13 cm; bracts submembranous ovate or lance-ovate 1-2.2 mm, caducous from young buds; pedicels at full anthesis slender 1.4-2.6 cm, the few fertile greatly thickened, in fruit becoming 2.5-4.5 cm; buds glabrous or almost so, the sepals sometimes minutely ciliolate; sepals firm yellowish or greenish obovate-suborbicular concave, weakly or sub- obsoletely (3-)5-nerved, unequal, the outermost ± half as long as the innermost, this (3.5-)4-6 mm; petals drying dull ocher-yellow, externally puberulent especially along the prominulous veins, subhomomorphic, oblong-oblanceolate or obovate 7-14 mm; stamens 7 homomorphic except for slightly unequal filaments, these 1-2.5 mm puberulent, the shallowly incurved anthers glabrous 2.8-5.5(-6) mm, truncate, the beak divaricate and not over 0.55 mm, sometimes subobsolete; ovary thinly pilosulous, abruptly contracted into an obliquely claviform, hollow stigma 0.7-1.8 mm diam, the ciliolate orifice 0.6-1.2 mm diam; ovules 4-seriate 130-194. Pod (scarcely known fully ripe) ascending on stiff pedicel, the stout stipe 3-4 mm, the body linear-oblong in outline, falcately or cyclically incurved, abruptly contracted at both ends, ±6-12 x 1.4-1.7 cm, strongly compressed laterally, the thick nigrescent glabrate valves flat at maturity and the X-section at middle I-shaped, the ventral suture intruded as a pithy partial septum; dehiscence (if any) unknown; seeds displaced into 2 double rows, one nearer and one further from the ventral suture, turned broadside to the thin blackish pulpy septa, symmetrically narrow-ellipsoid ±4-4.8 mm, the brown testa smooth but not highly lustrous, exareolate.

Variety Key - Key to the Varieties of S. ruiziana 1. Fls relatively ample, the petals when fully expanded (8-)9-11.5 mm; anthers 4-5.5(-6) mm; Ecuador, extreme s.-e. Colombia, and trans-Andine Peru s. to Junm and the Mantaro valley in Huancavelica (0-13°S). 25a. var. ruiziana (p. 152). 1. Fls small, the petals ±7 mm; anthers 2.8-4 mm, almost beakless; s.-e. Peru (Cuzco) and Bolivia (lat. 13-17°S). 25b. var. micrandra (p. 152).

Discussion

Senna ruiziana is the commonest cauliflorous member of ser. Bacillares in western Amazonia, notable for flowers disproportionately small for the ample leaves, which bear behind the pulvinules of the distal pair of leaflets a glandular- thickened seta. The relatively short erect, falcately bent or almost annular, laterally flattened pod containing well over one hundred seeds doubled up into two rows on each side of a shallowly intruded septum is unique, so far as known, in the series. Groups of populations situated to the north and south of latitude 13°S have evolved into taxonomically distinct units.