Mimosa incana (Spreng.) Benth.
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Authors
Rupert C. Barneby
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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.
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Family
Mimosaceae
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Scientific Name
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Type
217. Mimosa incana (Sprengel) Bentham, J. Bot. (Hooker) 4: 387. 1841. Acacia incana Sprengel, Syst. veg. 3: 137. 1826.-"Brasil., Sello."-Holotypus, Sello s.n., +B = F Neg. 28216, reproduced by Burkart, 1964, lam. II!; isotypus, BM! -Acacia sprengelii Hook
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Synonyms
Acacia incana Spreng., Acacia sprengelii Hook. & Arn., Mimosa pilulifera Benth., Mimosa sprengelii DC., Mimosa crassipes Arechav.
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Description
Species Description - Unarmed, broad-crowned arborescent shrubs 2-4 m, the freely branched young stems, lf-axes and peduncles densely tomentulose with erect rufescent plumulose setulae 0.1-0.4 mm, the lfts concolorously gray-stellate-tomentulose overall, the numerous small globose capitula solitary and more often geminate in lf-axils of terminal branchlets, forming an ample foliate panicle. Stipules erect linear-subulate 2—6 x 0.3-0.8 mm, becoming dry fragile, tardily deciduous. Leafstalks (2-)3-9(-10) x 0.3-0.5 mm, narrowly grooved ventrally, spicule 0; pinnae 1-jug., the rachis of longer ones (1.5—)2—3(—5) cm, the interfoliolar segments 1-2.2 mm; lfts of longer pinnae 12-24(-25)-jug., subdecrescent at each end of rachis, the first pair 0.2-0.4 mm distant from subulate paraphyllidia 0.2-0.6 mm, the blades oblong-elliptic or oblong obtuse from obtusely auriculate base, the larger ones ± 3—9(—11) x 1- 3.2(-4) mm, 2.3-3.5 times as long as wide, all faintly 1 -nerved beneath, the midrib subcentric, simple or in some ample lfts faintly pinnate. Peduncles 5-12 mm; capitula without filaments 5-7 mm diam., prior to anthesis moriform, the obtuse fl-buds densely gray-stellate; bracts sub- linear 1-1.5 x 0.2 mm, tomentulose dorsally, tardily deciduous; flowers 4-merous 4-androus, most of them bisexual; calyx campanulate membranous brownish glabrous 0.55-0.9 x 0.45-0.8 mm, the rim truncate or obscurely undulate-denticulate; corolla narrowly vase-shaped 2.4-3 mm, the firm concave lobes 1-1.2 x 0.65-0.8 mm; filaments pink when young, fading whitish, monadelphous at base into a tube ±1.5 mm enclosing the smooth ovary, sometimes alternating with vestigial staminoda, exserted 3-4 mm. Pods 1- few per capitulum, sessile, narrowly oblong 818 x 4-8 mm, nearly straight, (l-)2-4-seeded, the replum 0.5-1.4 mm wide, the firm valves scarcely elevated over seeds, the replum and valves alike densely or discontinuously, coarsely hispid with subcontiguous or discrete, erect-incurved stout-based, glabrous or either basally or apically puberulent, yellowish setae ± 1.5-2.5 mm sometimes mixed with fine stellulae, the cavity interrupted between seeds by tenuous transverse septa, the ripe valves separating from replum and tardily or reluctantly breaking into dehiscent articles ± as long as wide; seeds discoid ± 3—4 mm diam.
Distribution and Ecology - In moist or swampy, either lowland or montane thickets, widely scattered over Rio Grande do Sul, Brazil s.-ward from 28°S (Lins, 1984, map) and extending s. into deptos. Livramento, Río Negro and Rivera, Uruguay.—Fl. (II-)V- X. — Vassoura branca.
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Discussion
As shown by Burkart (1964, l.c.), M. incana is readily distinguished from related and habitally similar Calothamnos by pink filaments monadelphous at base and a burrlike fruit coarsely hispid overall with broad-based, subcontiguous or sometimes discrete setae. The very similar M. berroi, closely sympatric with M. incana in Uruguay and adjacent Rio Grande do Sul, is said to be a smaller shrublet, certainly different in having yellow filaments free to base and an apically dilated, not filiform style. The present treatment closely follows that of Burkart (1964), who unravelled the confused history and nomenclature of the species. Lins (1984: 35) cited, perhaps inadvertently, as M. incana the Paraguayan collections Hassler 4583, 9244 and Fiebrig 5629, all representing the distinct (though also pink-flowered) M. flocculosa Burkart, the last being isotypic. I have no evidence that genuine M. incana extends to Paraguay.
The typus of M. incana was a Sello collection lacking serial number and of unrecorded provenance. Malme (1931: 12) cited a Sello 3219 from Rio Grande do Sul, perhaps part of the type-collection of Acacia incana Sprengel, but gave no exact locality.
Fruits of M. incana are inordinately variable in width of valves and replum and in density, length and scabrous ornamentation of the setae on the valves. I have not the material to determine whether this variability is related to dispersal or to habitat. Sterile, galled fruits, often forming dense spherical clusters (Berro 4628, K), have been described by Burkart and Lins.
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Distribution
Brazil South America| Rio Grande do Sul Brazil South America| Uruguay South America|