Mimosa tandilensis

  • Title

    Mimosa tandilensis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Mimosa tandilensis Speg.

  • Description

    375. Mimosa tandilensis Spegazzini, Contr. fl. Tandil 13. 1901 . — "[Argentina. Buenos Aires:]. . . bastante común en todos los cerros [del Tandil]."—Syntypi, Spegazzini 663, 664, LPS = Burkart, 1948, lam. XIV!

    M. tandilensis sensu Burkart, 1948: 134 + antecedent bibliography, fig. 19T; 1967: 445, fig. 138F-I.

    Commonly diffuse or prostrate but not adventitiously rooting, microphyllous shrublets scarcely 1 m, randomly armed on intemodes with straight, broad-based aculei to 4.5 mm and the stems and peduncles at once retrostrigose with coarse, minutely calcarate setae to ±1-1.5 and minutely puberulent, the dorsal face of pinna-rachises forwardly strigose, the globose capitula solitary and few geminate in distal lf-axils. Stipules narrowly triangular ±2 mm, 3-5-nerved, persistent. Leaf-stalks not over 2 mm, reduced to pulvinus or almost so; pinnae 1 -jug., the rachis 4-14 mm, the interfoliolar segments 0.5-0.8 mm; lfts (7-)9-16-jug., decrescent proximally, the small first pair close to minute subulate paraphyllidia, the blades narrowly elliptic-oblong subacute, those near mid-rachis ±3-4.5 x 0.71 mm, all dorsally 2-nerved from pulvinule, glabrous facially, continuously pallid-marginate and setose-ciliolate. Peduncles 3-10(-"20") mm; capitula without filaments ±4.5 mm diam., prior to anthesis moriform, the bracts linear-oblanceolate 1-nerved, shorter than the puberulent fl-buds; flowers 4-merous 4-androus; calyx membranous campanulate ±0.15 mm, obscurely lobulate; corolla ±2 mm, the ovate-triangular subacute 1-nerved lobes 0.7-0.8 mm; filaments pale pink, free to base, exserted ±2 mm. Pods 1-6 per capitulum, sessile, in profile linear 6-20 x 3.5-4 mm, (l-)2-4(-"6")-seeded, the slender replum shallowly undulate, the papery valves low-colliculate over each seed, when ripe breaking up into free-falling, individually dehiscent articles ±3 mm long; seeds "3-3.5" mm (not seen).

    In rock-crevices and on stony hillsides, 250- 1000(?) m, reportedly common on Sas. del Tandil and less so on Sas. de Curumalal and de la Ventana in lat. ±37°-38°30'S in s. Buenos Aires, Argentina, and reported by Burkart (1948: 136) from Pta. Ballena near Maldonado in s. Uruguay.-Fl. IX-XI, III-IV.

    This account of M. tandilensis is based largely on the careful and comprehensive studies of Burkart, cited above. I remain sceptical, however, as to whether M. tandilensis is specifically distinct from the certainly very closely related M. ramulosa, of which Burkart had no distinct knowledge. The latter is described as an erect, stiffly and flexuously branched shrub attaining two meters in height, whereas M. tandilensis normally has humifuse or diffusely trailing stems less than one meter long (exceptionally erect when sheltered). In leaf-formula, leaflet-venation, flower, and fruit the two species are essentially identical. The nature of the relationship can be determined by field-study.