Senna birostris var. arequipensis (Vogel) 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 birostris var. arequipensis (Vogel) H.S.Irwin & Barneby

Type

Holotypus, collected at Arequipa IV. 1831 by F. J. F. Meyen, †B = F Neg. 1648; no isotypus found.

Synonyms

Cassia arequipensis Vogel, Cassia tarapacana Phil.

Description

Variety Description - Bushy shrubs 0.5-1.5 m, pilosulous throughout with spreading-incurved gray hairs 0.2-0.4(-0.5) mm, the pallid olivaceous thick-textured lfts subconcolorous, equally pubescent on both faces, the racemes forming a subcorymbose panicle; stipules linear-attenuate, linear or setiform 2.5-7.5 x 0.2-0.5 mm; lvs (4.5-)5.5-10 cm; petiolar gland either between or more often above first pair of lfts, sometimes displaced to the second pair; lfts 9-12(-14) pairs, on pulvinules 0.3-0.8(-1) mm, in outline oblong-ovate- or obovate-elliptic, the longest (6-)7-13(-17) x 3-6 mm, 1.5-2.6(-3) times as long wide, veinless except for dorsally prominulous midrib; racemes (5-)7-20(-25)-fld; sepals not strongly graduated, fuscous or purplish except for pallid margins, elliptic-obovate, the outer glabrous or dorsally puberulent 4.5-6(-7) mm, the inner glabrous 5.5-7.5(-8.5) mm; petals up to 11.5-14 x 6-10 mm; filaments of 2 latero-abaxial stamens 5-9 mm, of the centric abaxial one 2.5-4 mm, the anthers of the lateral ones (4.5-)5-6.8 mm, of the centric one plump but slightly shorter, 4-5 x 1-1.2 mm; ovary densely white-strigulose; style 2-2.7(-3.4) mm; ovules 8-16; stipe of pod 4-8 mm, the linear-oblong straight body 4.5-9.5 x 0.8-1.3(-l .5) cm, the seminal locules 5-5.5 mm long.—Collections: 14. [Key: "Anthers of 3 abaxial stamens all fertile, of ± equal length (4-7.8 mm) and girth even though the centric one is raised on a shorter filament than its neighbors; style 1.2-2.7(-3.4) mm. Lfts pilosulous on both faces and small (the longest 7-17 mm); Pacific slope of Andes from s.-w. Peru (Arequipa) to n. Chile (Tarapaca)."]

Distribution and Ecology - Dry rocky hillsides, banks of ravines, sometimes colonial along watercourses in alluvial gravels, ascending into the puno formation, 2200-3900 m, locally plentiful on the w. slope of the Andes in s. Peru (Arequipa, presumably also Moque- qua and Tacna) and adjoining Chile (n. Tarapaca).—Fl. irregularly through the year.

Discussion

The var. arequipensis is distinguished technically from other varieties of S. birostris by the gray pilosulous vesture of the leaflets, which are at the same time relatively small, thick-textured, apparently veinless except for the dorsally prominulous midrib, and borne on short pulvinules (0.3-0.8, rarely-1 mm), often appearing sessile against the rachis. It is obviously very closely related to the glabrate and less xeromorphic var. birostris, vicariant northward, mostly at lower elevations, along the Peruvian coast as far as La Libertad. This has a calyx of essentially the same size and proportions, the same long-stalked abaxial anthers, and the same (nearly always) broad and (always) long-stipitate pod; but green, thin-textured leaflets visibly penniveined dorsally. The also similar var. helveola of the central Peruvian Andes has, with the same pod and androecium, ventrally glabrous, dorsally penniveined leaflets and strongly graduated sepals hairy on the back. The type-collection of Cassia tarapacana agrees in every detail with some flowering specimens of var. arequipensis from Arequipa.

Distribution

Arequipa Peru South America| Tacna Peru South America| Moquegua Peru South America| Tarapaca Chile South America|