Monographs Details: Mimosa uraguensis Hook. & Arn.
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
Synonyms:Mimosa implexa Benth.
Description:Species Description - Widely densely branched shrubs attaining 3 m, randomly armed on internodes with 1-3 straight, ascending or horizontal straight aculei 2-7 mm (but some branchlets unarmed), either glabrous throughout or minutely vestigially glandular-setulose on growing tips and lf-stks, the smooth brown older stems and concolorous thick-textured lfts quite glabrous, the globose capitula on solitary peduncle axillary to coeval lvs below the branch-tips. Stipules ovate or triangular-cordate 1-3 x 1-2 mm, 1-nerved, persistent. Leaf-stalks 5-18(-20) mm, the petiole and interpinnal segments 3-9 mm, the ventral groove continuous between pinna-pairs (spicules 0); pinnae 1-2 (-3)-jug., the rachis 7-20 mm; lfts of longer pinnae 8-13-jug., either opposite or alternate along rachis, the first pair 0.7-2.5 mm distant from an unequal pair or from the one exterior solitary paraphyllium, these ovate-cordate or suborbicular 0.4-0.8 mm, the lft-blades oblong or narrowly oblong obtuse, the longer ones 4-6 x 1-2.7 mm, ±2.3-4 times as long as wide, all nerveless above, the subcentric midrib and 1-2 posterior nerves sometimes weakly prominulous beneath. Peduncles 1.5-3.5(-4) cm; capitula without filaments 4.5-6 mm diam., prior to anthesis moriform, the obtuse fl-buds thinly minutely capitellate-glandular; bracts obovate ± 1 mm; flowers normally 4-merous 8-androus; calyx membranous campanulate 0.55-0.95 mm, glabrous externally, the rim minutely denticulate; corolla narrowly vaseshaped 2.8-3.3 mm, the ovate 1-nerved lobes 0.7-0.9 mm; filaments vivid pink, free, exserted 4.5-6 mm. Pods 1-5 per capitulum, subsessile but sometimes attenuate at base, the linear-oblong body when well fertilized 20-45 x 4-6 mm, 4-7-seeded, the almost straight replum ±0.7 mm diam., the firm, smooth and glabrous, or minutely glandular, or rarely at once glandular and thinly setulose valves low-colliculate over each seed, when ripe separating entire from replum or at times tardily and imperfectly fractured between one or more pairs of seeds.

Distribution and Ecology - Forming riparian thickets along and below the high water line, local along the banks of río Uruguay between ±29° and 33°S latitude in e. Corrientes and Entre Rios, Argentina, in adj. Uruguay, and to be expected in s.-w. comer of Rio Grande do Sul, Brazil.—Fl. X-I(-II).

Discussion:

While the foregoing description of M. uraguensis is derived directly from specimens, the concept of the species owes everything to Burkart’s exemplary revision (1948, l.c.). Glabrous leaflets, alternate along the pinna rachis in most or many leaves, an essentially valvate dehiscence of the pod, and particularly an adaptation to intermittently flooded banks of the Uruguay River are the principal diagnostic features in the context of ser. Stipellares. I differ from Burkart only in reverting to the original spelling of the epithet, evidently intentional because Hooker referred to the country itself as Uraguay. The variant spelling reappears also in Inga uraguensis Hook.

 

Distribution:Brazil South America| Rio Grande do Sul Brazil South America| Uruguay South America| Argentina South America| Entre Ríos Argentina South America| Corrientes Argentina South America|