Senna scabriuscula

  • Title

    Senna scabriuscula

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna scabriuscula (Vogel) H.S.Irwin & Barneby

  • Description

    139.  Senna scabriuscula (Vogel) Irwin & Barneby, stat. nov. Cassia occidentalis var. (y?) scabriuscula Vogel, Syn. Gen. Cass. 21. 1837.—"In Brasilia: Sellow leg."—Holotypus presumably †B; neoholotypus, Sellow s.n., K! = NY Neg. 1456.

    Cassia neglecta var. entreriana Grisebach, Abhandl. K. Ges. Wiss. Gottingen 24 [=Symb. Fl. Argent.]: 116. 1879.—"655 . . . E[ntrerios]: Entrerios, in arenosis pr. Concordia ubique."— Holotypus, P. G. Lorentz N.E. 739, collected 13.11.1876. GOETT! isotypi, CORD (seen by Burkart, 1972, l.c. infra), W!—C. occidentalis var. entreriana (Grisebach) Burkart, Darwiniana 17: 594. 1972.

    Coarse leafy herbs from blackish roots, commonly appearing glabrous, but the obtusely angulate stems distally and all axes of inflorescence at least thinly strigulose-pilosulous with subappressed or incurved-ascending hairs up to 0.2-0.4(-0.5) mm, the stems sometimes in addition randomly pilose with fine lustrous setae up to 0.7-3 mm, the lfts usually scabrid beneath with minute scattered thickened trichomes and rarely also finely pilosulous, above glabrous or exceptionally puberulent, always coarsely ascending-ciliolate, the narrow terminal thyrse of few-fld racemes either entirely exserted or leafy-bracteate proximally.

    Stipules erect submembranous green or purplish triangular- or broadly lance- acuminate ±2-5 x 1-2 mm, very early caducous, absent from many spms.

    Lvs 8-25 cm; petiole including discolored pulvinus mostly (3-)6-21 mm, or where the small proximal pair of lfts lacks becoming longer (to 3 cm), at middle 0.8-1.8 mm diam, deeply openly grooved ventrally; rachis (4.5-)5-12.5 cm, its subulate terminal appendage glandular-thickened at base on ventral side; gland contiguous to pulvinus, sessile or obscurely stipitate, squatly ovoid or subglobose 1.2-2 x (0.7-) 1-1.5 mm; lfts 5-7(-8) pairs, accrescent distally, the distal pair lance- or narrowly ovate-acuminate obtuse mucronulate or acute 3.5-7.5 x (0.7-)0.85-1.5 cm, (3-)4-6.3 times longer than wide, the midrib immersed above, cariniform beneath, the 9-15 pairs of camptodrome with weak intercalary secondary veins beneath firmly sharply prominulous, above prominulous only near costa, thence immersed, the tertiary venulation invisible above, faintly discolored but not or scarcely raised beneath.

    Peduncles 3-10 mm; racemes short, often subumbellately (1-)2-6(-8)-fld, the axis including peduncle becoming (3-)7-12(-16) mm; bracts ovate-acuminate or lance-caudate 2.5-6 x 1.2-2 mm, caducous from below young fl-buds; mature pedicels 14-22 mm; fl-buds nodding, glabrous beyond hypanthium; sepals submembranous pallid, fuscous- or purple-tinged, obovate or oblong-obovate obtuse, the outermost 5-8 mm, the longest inner one 8.5-12 mm; petals deep yellow drying whitish brown-veined, of ± equal length, the 3 abaxial obovate obtuse or flabellate-obcordate, the 2 abaxial oblanceolate, the longest petal (13-) 14.5-20 mm; androecium glabrous, the spatulate staminodes 1.4-1.8 mm wide, the filaments of 4 median stamens 1.6-2.5(-3.5) mm, of 2 large abaxial ones 5.5-9 mm, of the sterile centric abaxial one 3-4 mm, the yellow anthers of 4 median stamens including the oblique, shortly 2-lipped beak (4-)4.3-6.2 mm, the castaneous or chocolate-brown anthers of the 2 latero-abaxial ones measured to base of beak 5-7 x (1.6-) 1.9-2.3 mm, their yellow beak 1.7-2.5 mm, its thickened tonguelike abaxial lip 1.2-2 mm, the anther of the centric abaxial stamen linear-oblanceolate 2.5-4 x 0.4-0.6 mm; ovary densely strigulose-pilosulous; style 3.8-5 mm, abruptly thickened and retrocurved at apex, there 0.45-0.7 mm diam, the stigmatic cavity introrse; ovules 46-60.

    Pod straight erect or gently incurved-ascending 10-15 x (0.55-)0.6-0.9 cm, essentially as that of S. occidentalis, the locules mostly 1.6-2.5 (some up to 3.5) mm long, always wider than long; seeds turned to present their areolate broader faces to the septa, broadly compressed-obovoid 3.9-5 x (2.5-)2.9-4 mm, the dull olivaceous testa microscopically papillate, the obovate or elliptic areole 2.2-3.2 x 1-1.8 mm.—Collections: 21.

    Sandy campo and derived riparian and ruderal habitats below 300 m, locally plentiful in the lower Parana and Uruguai valleys between 25° and 35°S latitude, in s. Paraguay, n.-e. Argentina (s.-e. Chaco, e. Sta. Fe, Corrientes, Entre Rios) and adjoining Uruguay, originally described from "Brazil," and to be looked for in w. Rio Grande do Sul; disjunctly (?) w. up Rio Pilcomayo to 450 m in s.-e. Tarija, Bolivia.—Fl. X-III(-IV).

    Senna scabriuscula occurs in two pubescence forms: in the commoner of these the leaflets are glabrous except for stiffly ciliolate margins and scattered thickened trichomes on the dorsal face, while the stems are either glabrate or thinly pilose with long shining bristles; in the other the leaflets are pilosulous on one or both faces but the stems lack setae. These two forms, which are sympatric near Concordia, type-locality of Cassia neglecta var. entreriana, have the same pod, which is essentially that of S. occidentalis, gently incurved and 46-60-ovulate, and we agree with Burkart (1972, l.c.) that the close affinity of the species lies in the direction of S. occidentalis and not of S. neglecta, with which Grisebach, who knew only the pubescent phase, associated it. Burkart earlier (1952, p. 164, in key) contrasted the annual root, 4-6 pairs of relatively broad leaflets and mostly axillary racemes of Cassia occidentalis with the perennial root, 5-7 pairs of narrower leaflets and thyrsiform inflorescence of C. neglecta var. entreriana, but these comparisons are effective only in the narrow context of the Argentine flora. We find, however, that S. scabriuscula differs further and more significantly from S. occidentalis in the narrow stipules and floral bracts, in the abbreviated petioles, in the generally (but not absolutely) longer sepals, in the broader staminodes and very stout long-beaked abaxial anthers, and most importantly in the style, which is thickened and incurved like that of S. hirsuta sens. lat. The ranges of fully extratropical S. scabriuscula and the largely intertropical S. occidentalis and S. hirsuta all overlap in southern Paraguay and it seems possible that the present species has arisen through hybridization, inheriting its involute stigma and unstabilized tendency to hairiness from S. hirsuta var. puberula and its pod and seeds from S. occidentalis. Whatever its origin, however, S. scabriuscula appears now to be an independently self-reproductive entity most appropriately treated at the level of species.