Mimosa pigra L.

Authors

Rupert C. Barneby

Authority

Barneby, Rupert C. 1991. Sensitivae Censitae. A description of the genus Mimosa Linnaeus (Mimosaceae) in the New World. Mem. New York Bot. Gard. 65: 1-835.

Family

Mimosaceae

Scientific Name

Mimosa pigra L.

Type

271. Mimosa pigra Linnaeus, Cent. pl. I: 13. 1755, based on Aeschynomene spinosa quinta Breyne, Exot. pl. cent. 44, t. 20. 1678 and Ae. spinosa quinta . . . seu foliis acaciae latioribus . . . J. Commelijn, Horti med. amstelod. 2: 59, t. 30. 1697, both de

Synonyms

Mimosa asperata L., Mimosa pellita Humb. & Bonpl. ex Willd., Mimosa asperata var. laevior DC., Mimosa vellosiella Herter, Mimosa asperata var. glabrior Hook. & Arn., Mimosa tweedieana Barneby ex Glazier & Mackinder

Description

Species Description - Diffuse and trailing, adventitiously rooting shrubs forming riparian thickets ±5-16 dm tall and of indefinite extent, erratically armed on stems, lf-stks and occasionally on peduncles with sharp recurved or only subdeclined, broad-based stramineous or fuscous aculei 0.7-5 mm (random branchlets unarmed) and thinly strigose with slender, forwardly appressed basifixed tapering setae ±1-2 mm commonly mixed with minute puberulence, the olivaceous, when dry brownish foliage appearing glabrous but the lfts commonly ciliolate near base and often minutely strigulose dorsally, the inflorescence an efoliate or proximally few-lvd pseudoraceme of small globose capitula exserted up to 15 cm. Stipules erect, ovate or lanceolate ±2-4.5 x 1-2 mm, the firm blades coarsely 7-10-nerved, either glabrous or gray-puberulent (but not setose) dorsally, commonly setulose-ciliolate, persistent. Leaf-stalks 4.5-10 cm, the petiole including pulvinus 5-13 mm, the longer interpinnal segments 9-18 mm, the interpinnal spicules (0.5-)l-7 mm; pinnae of larger lvs 4-8(-10)-jug., decrescent proximally, the rachis of longer ones (2.5-)3-6 cm, the longer interfoliolar segments 1.2-2 mm; lfts of longer pinnae 20-35-jug., decrescent at each end of rachis, the blades linear or linear-oblong from obtusangulate base, mostly obtuse apiculate, those near mid-rachis 5.5-10.5 x 1.1-2.5 mm, ±3.6-6 times as long as wide, all ±6-nerved from pulvinule, the slightly displaced midrib weakly 1-2- branched on each side, the adjacent anterior and posterior nerves usually expiring short of blade apex but sometimes attaining it, the outer posterior ones much shorter. Peduncles l-4(-5) per node of inflorescence, 7-17(-24) mm; capitula without filaments 5-6.5 mm diam., prior to anthesis moriform, the obtuse fl-buds densely scaberulous-setulose; bracts oblanceolate, less than 1.5 mm, 1-nerved, minutely ciliolate; flowers almost of M. pellita but slightly smaller, the ciliolate but scarcely paleaceous-lobulate calyx ±0.6-0.85 mm, the corolla 1.5-1.8 mm; filaments pink, the longer set exserted ±2 mm. Pods solitary and to six per capitulum, either sessile or narrowed at base into a stout stipe to 3 mm, the body in profile broad-linear 40-90 x 10—16(—17) mm, planocompressed except immediately over each of 6-12(-15) seeds, the replum 0.6-0.9 mm wide, the papery fuscous valves thinly strigose with fine, forwardly appressed tapering setae to ±1 mm and often also microscopically puberulent, when ripe breaking up into transversely oblong or almost square, free-falling, individually indehiscent articles 5— 10(— 12) mm long; seeds elliptic-oblanceolate, in broad view ±5.5-7 x 3-4.5 mm, proportionately broader than those of M. pellita, the olivaceous testa similar.

Distribution and Ecology - On muddy and sandy river-banks and estuary shores, below 150 m, locally abundant along río Paraná from near 22°S in Paraguay s. to the delta and the s. shore of río de la Plata at ±35°S in Argentina.—Fl. XI-IV, and randomly through the year. Map 36.

Discussion

I am in full accord with Burkart (1948, l.c.) that the riparian mimosa of the Paraná valley that he described and figured under the title of M. vellosiella is a distinct entity peripheral to closely allied M. pigra auct. (M. pellita of this account), and in the context of its relatives best accorded specific status. Relatively low stature, adventitiously rooting stems, relatively few pinnae and few, well-spaced leaflets, thin appressed vesture, and broad papery pod consisting of relatively broad articles enclosing proportionately broader seeds distinguish it. I differ from Burkart in the belief that it is endemic to Paraguay and Argentina and that it is replaced on the Atlantic coast of southern Brazil by a sibling species M. elliptica, differing in glabrous corolla and much longer filaments. The vexed nomenclature of the group has been analyzed elsewhere (Barneby, 1989). The epithet vellosiella is typified by an illustration in Vellozo’s Icones, based presumably on a plant from the vicinity of Rio de Janeiro, and therefore not applicable to the species considered here. Mimosa pigra Linn., based on figures of a plant grown in Holland in the XVII century, is the oldest name for any member of the group dominated by polymorphic M. pellita. The name is here applied to the species of La Plata estuary on the basis of similarity in leaf-formula, thin appressed vesture and relatively distant leaflets not found elsewhere in the complex.

Distribution

Argentina South America| Paraguay South America|