Monographs Details: Mimosa sparsiformis Barneby
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 sparsa Benth.
Description:Species Description - Erect, stiffly branched shrubs attaining 1-2 m, either unarmed or more often armed on internodes with two infrastipular and one distantly displaced infrapetiolar, straight horizontal or widely ascending, broad-based aculei 2-7 mm, the terete reddish stems glabrous except for rare, sharply deflexed basifixed setae ± 1 mm, the pinna-rachises thinly antrorse-setose, the peduncles either glabrous or charged under the capitulum with a few deflexed setae, the lfts quite glabrous facially, subcontinuously marginate and setose-ciliate, the globose capitula solitary and paired in many lf-axils, sometimes briefly pseudoracemose prior to anthesis but immersed in fruit. Stipules firm erect, lance-acuminate 3-5 x 0.6-1.2 mm, prominently 3-5-nerved dorsally, thinly setose-ciliolate or glabrous, persistent. Leafstalks of larger lvs 7-17 x 0.3-0.4 mm, obscurely sulcate; spicule 0; pinnae 1-jug., the rachis 1535 mm, the longer interfoliolar segments 1-1.7 mm; lfts of larger lvs 17-22-jug., decrescent near each end of rachis, the first pair 0.7-1.5 mm distant from subulate paraphyllidia 0.3-0.8 mm, the blades linear-oblong from obtusangulate base, subacute at apex, straight or slightly arched forward, those near mid-rachis 5.5-10.5 x 1.2-1.8 mm, 4.2-5.5 times as long as wide, all 2-3-nerved from pulvinule, the slightly displaced midrib and the posterior nerve of almost equal strength, the latter produced almost to blade apex, the outer posterior one very short or obsolete. Peduncles (1-) 1.5-3 cm; capitula without filaments 6-6.5 mm diam., prior to anthesis moriform, the obtuse fl-buds cinereously antrorse-strigulose between four glabrous keels; bracts lance-ovate incurved 0.5-1 mm, prominently 1-nerved dorsally, minutely ciliolate, persistent; flowers 4-merous 4-androus, most bisexual; calyx rudimentary 0.1-0.15 mm, the rim undulate or microscopically denticulate; corolla narrowly claviform (2. l-)2.4-3.1 mm, the erect, concave but not thickened, ovate lobes (0.6-)0.8-1 x 0.5 mm; filaments pink, free above an obscure stemonozone, exserted 5-7 mm; ovary glabrous. Pods (described by Burkart) 15-25 x 5-6 mm, 2-4-articulate, the valves glabrous, the replum shortly thinly setulose.

Distribution and Ecology - In moist disturbed thickets and on stream banks, 500-950(-?) m, apparently common on the n. tributaries of rio Jacui between 50°30' and 53°W in n.-e. Rio Grande do Sul, Brazil, thence n. to lower Pelotas valley in s.-centr. Sta. Catarina.-Fl. XII-IV.

Discussion:

Burkart (1979, l.c.) has described this species under the name M. sparsa, which he seems to have known exclusively through the Field Museum photograph of the isotype at Berlin. I have seen three surviving duplicates of this, all of which differ from M. sparsiformis in smaller simpler leaves and, in particular, in one-nerved leaflets girdled by a simple continuous pallid margin bereft of cilia. As already known to Burkart, M. sparsiformis occurs in armed and unarmed states, which perhaps deserve some taxonomic recognition. Although not known to occur sympatrically, the ranges of these forms are not significantly different overall. Field observation is required.

Distribution:Brazil South America| Santa Catarina Brazil South America| Rio Grande do Sul Brazil South America|