Senna pistaciifolia

Title

Senna pistaciifolia

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Senna pistaciifolia (Kunth) H.S.Irwin & Barneby

Description

153.  Senna pistaciifolia (Humboldt, Bonpland & Kunth) Irwin & Barneby, comb. nov. Cassia pistaciifolia Humboldt, Bonpland & Kunth, Nov. Gen. & Sp. 6(folio): 349 ("pistaciaefolia "). 1824.—Typus infra sub var. pistaciifolia indicatur.

Amply leafy shrubs with smooth terete hornotinous branches and branchlets, at anthesis mostly 0.8-2.5 m, reportedly sometimes arborescent to 10 m, often appearing and sometimes truly glabrous but the young stems, lf-stalks, lower face of lfts and axes of inflorescence sometimes puberulent or pilosulous with weak hairs up to 0.4-0.7 mm, the stiffly membranous lfts dull olivaceous on both faces, paler beneath, the loosely many-fld racemes at first axillary to distal lvs, then either immersed in foliage or exserted, some smaller later ones often forming a terminal depauperately leafy or leafless panicle.

Stipules (caducous, poorly known) firm erect obliquely lance-acuminate 3-12 x 1.5-3 mm, ± dilated at base on the side further from petiole, strongly striate-nerved.

Lvs (0.7-)l-4 dm; petiole including moderately swollen pulvinus (1-)2.5-7 cm, at middle 0.7-2.3 mm diam, rounded dorsally, very narrowly thick-margined and plano-sulcate ventrally; rachis (2-)3-24 cm; petiolar glands 0; lfts 3-10(-11) pairs accrescent distally but the penultimate one sometimes largest, this and the distal pair broadly oblanceolate, oblong-obovate or elliptic (3.5-)4.5-10.5 x (1.2-) 1.5-4.7 cm, ±2-3 times as long as wide, at apex broadly rounded, deltate or (if damaged) emarginate, commonly conspicuously mucronate, at base (when relatively broad) inequilaterally rounded or subcordate or (when narrower) cuneate on the distal side, the midrib centric straight, the 10-16 pairs of camptodrome (and often random intercalary) secondary veins with tertiary and reticular venulation all prominulous on both faces, a trifle more sharply so dorsally, there going out into a raised mesh of areoles variable in size but the smallest 0.5 mm or less diam.

Racemes loosely 10-45 fld, the axis together with peduncle becoming (0.5-)0.7-3 dm; bracts firm, not or scarcely colored, ovate apiculate or ovate- or lance-acuminate, together forming around the very young fl-buds a small cone, caducous as the pedicels begin to elongate, absent from many flowering and all fruiting spms; pedicels at and after full anthesis 12-20 mm; fl-buds obliquely obovoid or oblong-obovoid obtuse, glabrous or thinly puberulent; sepals little graduated, oblong or obovate obtuse 8-14.5 mm, either yellowish or fuscous, membranous-margined, the tips cucullate; petals yellow with darker veins, when dried whitish brown-veined, glabrous, heteromorphic, all 3 adaxial or only the vexillar petals oblanceolate to narrowly obovate, the 2 lateral sometimes and 2 abaxial always obovate, the latter obliquely so and usually largest, the longest petal 15-22 mm; androecium glabrous, the filaments of 4 median stamens 1.3-2.5 mm, of 3 abaxial ones 3-5.5 mm, those of 2 latero-abaxial ones much thickened, the anthers of 4 median stamens oblong, dorsoventrally compressed, little incurved 3-5 mm, abruptly contracted into a porrect biporose beak 0.7-1.4 mm, those of the 2 latero-abaxial ones lunately incurved 13-16 mm, at base inequilaterally sagittate (the longer descending spur 2.5-3 mm), at apex very slightly contracted below a short 2-lipped beak, the upper lip 2-porose, the central abaxial anther sterile, 2.5-3 mm, its basal lobes spreading-decurved ±1 mm; ovary either glabrous or strigulose; style 4.5-6.5 mm, subfiliform slightly dilated toward the gently incurved apex, 0.2-0.4 mm diam just below the oblique stigma; ovules (17-) 18-30.

Pod obliquely declined, the stipe 3.5-5 mm, the oblong piano-compressed body (7-)8- 12 x 1.6-2.4 cm, the papery glabrous or early glabrate valves greenish with fuscous stripe down middle, finely venulose, tardily separating along the scarcely thickened sutures, the inter seminal septa 3.5-5 mm apart, forming locules 7-16 mm wide extending transversely across 2/3to nearly the whole width of the cavity; seeds (not seen ripe) horizontal to the pod’s long axis, apparently narrowly obovate compressed parallel to the valves, the areole oblong-elliptic occupying more than half the seed-face.

The material that has accumulated in herbaria under the names Cassia pistaciifolia, C. fraxinifolia (considered by Bentham only varietally distinct from the preceding), C. pearcei and C. picta appears to represent a single major specific entity. All have essentially the same perianth and characteristic androecium, and the same pod except for some variation in width of the seed-locules and in degree to which the valves are elevated over the seeds. These minor features of the pod, however, are sufficiently correlated with variation in pubescence, number of leaflets, venation of the bracts and dispersal to justify the recognition of three varieties.

Key to the Varieties of S. pistaciifolia

1. Bracts puberulent dorsally, faintly keeled but not prominently several-nerved; lfts (3-)4-6(-7) pairs, their midrib ± depressed-sulcate ventrally, their margin subrevolute; centr. Ecuador n. through Cauca valley to n.-w. Colombia (Antioquia).

153a. var. pistaciifolia (p. 472).

1. Bracts glabrous, prominently 5-several-nerved dorsally; lfts variable in number, but the midrib prominulous ventrally and the margin plane; s. Ecuador to Bolivia and Galapagos Is.

2. Lfts 6-11 pairs, at least in most larger lvs; pod plane, the valves indistinctly elevated over the seeds as faint corrugations; n. Peru (Lambayeque, Cajamarca and Amazonas) to Bolivia, on the Amazon slope except marginally at the n.-w. limit.

153b. var. glabra (p. 473).

2. Lfts 3-8, in most upper lvs not over 6 pairs; valves of ripe pod colliculately elevated over each seed, the colliculi confluent into a low crest along middle of pod; Pacific n.-w. Peru (Piura), Pacific s.-w. Ecuador and Galapagos Is.

153c. var. picta (p. 473).