Monographs Details: Mimosa ostenii Speg. ex Burkart
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
Description:Species Description - Arborescent shrubs 2-5 m armed on random internodes of stiffly flexuous, terete but obtusely ribbed branches with a solitary, gently recurved infrastipular aculeus 2-6 mm, appearing glabrous but the young growth and inflorescence minutely puberulent and reddish-granular, the lvs dark green subconcolorous glabrous, the globose capitula either solitary or 2-3 together, either in axil of coeval lvs or on short lateral branchlets, almost never on scaly brachyblasts. Stipules appressed to stem, narrowly subulate 0.5-1 mm, either deciduous or persistent. Leaf-stalks including pulvinus 1-9(-11) mm, rounded dorsally, openly sulcate ventrally, the sulcus bridged and vestigially spiculate at apex; pinnae 1-jug., the rachis of longer ones 12-25 mm, the longer interfoliolar segments 1.2-2.5 mm; lfts 7— 11 (— 12)-jug., scarcely graduated, the first pair 0.8-2 mm distant from minute papilliform paraphyllidia, the blades narrowly oblong obtuse, the largest 5-8(-9) x 1.5-3 mm, 3-4.2 times as long as wide, all nerveless ventrally, faintly 1 (-2)-nerved dorsally, the almost immersed midrib subcentric beyond mid-blade, the posterior nerve obscure or very short. Peduncles 5-18 mm; capitula without filaments 6-8 mm diam., prior to anthesis moriform; bracts linear-spatulate or -oblanceolate ±1 mm, deciduous; pedicels 0-0.2 mm; flowers 4-merous 8-androus; calyx membranous turbinate-campanulate 1-1.8 mm, the tube of thinner texture below the sinuses than below the lobes, these obovate or obtusely triangular 0.2-0.3 mm, dorsally convex and puberulent; corolla whitish, narrowly vase-shaped 3.3-3.8 mm, the ovate acute 1-nerved lobes 1.1-1.3 mm; filaments white, shortly monadelphous around stipe of ovary, exserted 3-3.5 mm. Pods essentially as those of M. detinens but the body (acc. Burkart) attaining 8 cm in length and the seeds to 7.

Distribution and Ecology - In campo thickets along streams and rivers, localized at low elevations along ríos Gualeguay, Gualeguaychu and Uruguay in lat. ±31°40- 33°20'S, in prov. Entre Ríos, Argentina, and adj. Uruguay.—Fl. XI-I.

Discussion:

A close affinity between M. ostenii and M. detinens was demonstrated in Burkart’s revision, to which I can add nothing of substance. The flexuous stems, greener and on the average coarser foliage and the somewhat larger capitula (without filaments 6-8, not 4.5-6 mm diam.), combined with a distinctive disjunct area of dispersal make identification of M. ostenii an easy matter.

Distribution:Argentina South America| Entre Ríos Argentina South America| Uruguay South America|

Narratives:Mimosa ostenii