Rhynchosia senna var. senna

  • Authority

    Grear, John W. 1978. A revision of the New World species of Rhynchosia (Leguminosae-Faboideae). Mem. New York Bot. Gard. 31 (1): 1-168.

  • Family

    Fabaceae

  • Scientific Name

    Rhynchosia senna var. senna

  • Description

    Variety Description - Stems to 50 cm, prostrate, ascending, rarely twining, puberulous, strigulose or villosulose. Stipules linear-lanceolate, 1.5-3 mm long, 0.5-1 mm wide. Petioles 3-15 mm, villosulose, strigulose or puberulous. Leaflets ovate, ovate-lanceolate or rhombic-lanceolate, base subcordate, 0.5-3 cm long, 0.3-1.7 cm wide, puberulous to strigulose or villosulose beneath, terminal petiolule 2-6 mm, the laterals subobsolete, stipels obscure to 0.5 mm. Inflorescences 7-20 mm, peduncle subobsolete, pedicels 3-10 mm, exceeding the petiole. Bracts setose or linear, 0.5-1 mm long, 0.5 mm wide. Calyx equalling or slightly less than the corolla, 5-8 mm, tube 2 mm, lobes acute, acuminate, 3-6 mm, vexillar sinus 2.5-4 mm. Corolla 7-9 mm. Standard widely ovate to obovate, puberulous, 7-8 mm long, 5-6.5 mm wide, auricles 0.5 mm, claw 1.5-2 mm. Wings oblong or ovate, puberulous, 1-2 mm wide, claw 2 mm. Keel blades 6-8 mm long, 2.5-3 mm wide, claw 2-2.5 mm. Stamens 6-8 mm. Fruits puberulous or puberulous-hirsutulous intermixed, 1.5-2.3 cm long, 4-6 mm wide, beak 1 mm. Seeds 3-4 mm long, 34 mm wide.

  • Discussion

    Rhynchosia senna Gillies ex Hooker, Bot. Misc. Hooker 3: 199. 1833, pro parte quoad typum. Dolicholus senna (Gillies ex Hooker) O. Kuntze, Rev. Gen. 3(2): 62. 1898, pro parte. Rhynchosia senna f minor Grisebach, Abh. Bohm Ges. Wiss. Goet. 19: 74. 1874. Type: ARGENTINA. “Cordoba, in collibus rupestribus pr. Las Penas, S. Francisco,” Collected by Grisebach (holotype, GOET, not seen). Rhynchosia senna var foliolis late ovatis Ball, Linn. Jour. Bot. 21: 216. 1884. Described from G. Claray 80, K! Type. ARGENTINA. ‘Tampas, in province of Cordova” J. Gillies sn, w/o date (lectotype selected, K!, pro parte, the four plants mounted at the top of the sheet, excl the plant at the bottom of the sheet = R. senna var angustifolia; isosyntype, K!, Gillies sn, pro parte, the plant mounted at the left of the sheet, excl the plant at the right of the sheet = R. senna var angustifolia). Local Names. Sen del zorro, sen del campo (Argentina: Buenos Aires); sen (Argentina: Córdoba); perotillo (Argentina: La Pampa). Rhynchosia senna var senna has a rather restricted distribution primarily in northern Argentina with a few isolated collections in adjacent Uruguay and Brazil, where it is sympatric with the more widely distributed var angustifolia. Although both taxa are polymorphic and share a large number of morphological characters, they also differ in other respects. Rhynchosia senna var senna has stems which are prostrate or ascencing but rarely twining, the leaflets are lanceolate-ovate to rhombic-ovate, the corolla is usually larger, the pedicel is extremely long, equalling or exceeding the petiole, and the calyx lobes are wide and elongate, equalling or exceeding the corolla. Rhynchosia senna var angustifolia has prostrate or twining stems which are rarely ascending, the leaflets are of two types (linear-lanceolate or rhombic-ovate), the corolla is usually shorter, the pedicel length does not equal that of the petiole, and the calyx lobes are usually more narrow and shorter than the corolla. Due to morphological similarities and sympatric occurrence, both varieties are often collected together and considered to be the same. For example, one collection (Losen 68) from the province of Cordoba in Argenina consists of six sheets seen by me. Five of them are var senna but one (LE) shows a mixture of both varieties, which also would indicate their sympatric occurrence. The two plants on the sheet, however, are quite distinct with respect to the distinguishing characters already mentioned. The type collection of var senna is also such a mixture of plants and a lectotype has been selected that fits the protologue of Gillies for R. senna. George Bentham has written on both type sheets in the Hooker Herbarium, "Rhynchosia senna Gill, (pro parte),” and on one sheet, “two species,” which indicates his awareness of the distinction. Rhynchosia senna var angustifolia was recognized as a distinct entity by Torrey & Gray in 1838 but was published as a new species, R. texana, rather than as a variety. In this revision, however, it is reduced to varietal status as R. senna var angustifolia. Rhynchosia senna var senna shows an affinity with R. diversifolia var diversifolia with respect to habit, leaflet shape and morphology, and inflorescence type. The two are frequently confused and a number of mixed collections exist, but R. diversifolia var diversifolia is not prostrate or twining and has straight, rather than curved, pods. I have seen what appears to be a few transitional forms, which might indicate intergradation of the two, but this is relatively rare and does not appear to be genetically fixed.

  • Distribution

    Distribution. Argentina, Uruguay and Brazil (Rio Grande do Sul) (Fig. 6). Occurring primarily in campos and pastures in the Pampas and on mid-slopes of mountainous areas at elevations of 1000-2020 m.

    Argentina South America| Uruguay South America| Brazil South America|