Senna purpusii (Brandegee) 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 purpusii (Brandegee) H.S.Irwin & Barneby

Type

Lectoholotypus, Purpus 107, UC (2 sheets)! paratypi, Nelson & Goldman 7160, NY, US!—Adipera purpusii (T. S. Brandegee) Britton & Rose, N. Amer. Fl. 23(4): 240. 1930.

Synonyms

Cassia purpusii Brandegee, Adipera purpusii (Brandegee) Britton & Rose

Description

Species Description - Bushy drought-deciduous, stiffly sometimes awkwardly branched but not thorny desert shrubs ±9-15 dm, the older stems clothed in gray fissured and flaking bark, the densely leafy annotinous branchlets castaneous or livid smooth, together with lf-stalks and dorsal face of lfts strigulose with fine appressed pale hairs up to 0.1-0.3 mm, the lf-stalks sometimes charged in addition with scattered thickened trichomes, the thick-textured foliage glaucous concolorous, the racemes axillary to lately expanded lvs on young branchlets, forming an irregular ± corymbose, usually shortly exserted panicle. Stipules erect, linear or linear-lanceolate, straight or subfalcate, 2-7 x 0.4-0.6 mm, the green or purplish blades early dry brunnescent deciduous. Lvs alternate on vigorous young branchlets and fasciculate on brachyblasts lateral to older ones, 2-5 cm; petiole slender, including the moderately swollen pulvinus (4-)6-15 mm, at middle 0.4-0.6 mm, terete except for narrow ventral groove; rachis 5-23 mm, the longer interfoliolar segments 4-9 mm; petiolar gland between proximal pair, slenderly or stoutly stipitate, in profile 1.5-2.5 mm, the ovate or lance-fusiform acute head reddish or livid (0.3-)0.4-l mm diam; pulvinules 0.6-1.4 mm; lfts of primary lvs 2-4, of brachyblast lvs 2 or 3 pairs, not or a little accrescent distally, the distal pair broadly elliptic or elliptic-obovate obtuse or emarginate (7-)9-19(-20) x (5-)6- 12 mm, 1.4-1.7 times as long as wide, at base inequilaterally rounded or subcordate, the margin plane, the blade except for dorsally raised midrib often apparently veinless, but 2-4 pairs of weakly camptodrome secondary venules sometimes faintly prominulous on either face. Racemes loosely 2-6(-9)-fld, the expanded fls elevated to or beyond level of buds, the axis including peduncle 1.5-5(-6) cm; bracts elliptic-oblong cymbiform 1.5-2.5 mm caducous; pedicels at full anthesis and afterward 12-22 mm; young fl-buds subglobose, puberulent or almost glabrous; sepals submembranous pinkish-fuscous hyaline-margined, not much graduated, all obovate or suborbicular, the outermost 5-7 mm, the innermost 6.5-8.5 mm; corolla zygomorphic, bright yellow drying yellow brown-veined, the vexillar petal and its 2 neighbors short- clawed 11-13 mm, their blades cordate at base and 9-10 mm wide, the 2 abaxial petals oblanceolate narrowed to a slender claw, ±13 x 5-6 mm; androecium glabrous, functionally 7-merous, the 3 staminodes 1.4-1.7 mm wide, the filaments of 4 median stamens 1.5-2.5 mm, of 3 abaxial ones 6.5-8 mm, the 7 fertile anthers thin-walled yellowish, those of 4 median stamens oblong nearly straight 3-3.5 x 1-1.2 mm, those of 3 abaxial ones gently incurved 3.7-4.3 x 1-1.3 mm, the centric one sometimes a trifle smaller, all anthers at apex obscurely strangulated but not beaked, obliquely truncate, 2-porose; ovary strigulose; style linear-filiform 3-4.5 x 0.2 mm, gently incurved but not or scarcely dilated distally, the stigmatic cavity minute terminal; ovules 7-10 (seldom all maturing). Pod obliquely pendulous, the stipe 5-8 mm, the body potentially broadly linear- oblong abruptly obtuse at both ends and 5-9 cm long, gently incurved, but frequently following abortion of ovules shorter and variously distorted, at fertile segments becoming 10-14 mm diam, laterally compressed but strongly turgid when ripe, bicarinate by the sutures, the papery, dull brown sometimes red-tinged valves delicately venulose toward the margins, inertly dehiscent basipetally through both sutures; seeds obliquely horizontal, compressed parallel to the valves but remaining plump, in profile broadly obovate or suborbicular-flabellate, emarginate distally, 7-10 x 6-9 mm, the testa smooth but dull, ochraceous-olivaceous, ultimately crackled, the areole oblong or elliptic 1.8-3 x 1.2-2 mm.— Collections: 18.—Fig. 25.

Distribution and Ecology - Desert flats, washes and canyon terraces, in matorral often incorporating Idria and Pachyconnus, 10-420 m, locally plentiful on the Pacific slope of Baja California between Punta Canoas and Calmallf (lat. 28-29°30'N).—Fl. primarily XII-IV(-VI), and also sporadically following rains.

Discussion

An ornamental desert shrub, its neat glaucous foliage contrasting happily with the corymbose panicle of golden yellow flowers, S. purpusii should be tested for cultivation in dry temperate gardens. The only Baja Californian senna at all similar in habit is S. polyantha, found further south on the peninsula; it may be distinguished at anthesis by the more numerous (at least 7, not 2-4) pairs of leaflets and subsequently by the piano-compressed (not turgid), marginally winged pod. Senna purpusii is taxonomically as well as geographically isolated, having no obvious relatives elsewhere in Mexico and only somewhat doubtful affinities with such western South American Pachycarpae as S. glaucescens or S. mandoni. Britton & Rose associated it in the genus Adipera with our S. septemtrionalis, S. pendula and their kindred (=our ser. Coluteoideae). From these it differs in the relatively few ovules and in the areolate seeds.

Distribution

Baja California Mexico North America|