Mimosa sensitiva L.
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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
322. Mimosa sensitiva Linnaeus, Sp. pl. 518. 1753.—Typus infra sub var. sensitiva indicatur.
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Description
Species Description - Diffuse, scrambling or scandent, vinelike soft-woody shrubs, densely armed on subterete but several-ribbed stems and on lateral and dorsal ribs of lf-stks with files of sharp recurved, stramineous or bronze-tipped aculei to 1-3 mm nearly always mixed with retrorse yellowish setaculei, in addition finely villosulous throughout except for often glabrous upper face of lfts and charged on lower face of lfts with scattered appressed setae to 0.8-1.6 mm, the olivaceous lvs subconcolorous or a little paler beneath, the globose or plumply ellipsoid capitula mostly solitary or paired in lf-axils, some later ones pseudoracemose and shortly exserted from foliage. Stipules ovate or lanceolate 2-5(-8) x 0.8-2 mm, sharply 3-nerved, dorsally villosulous and sometimes also setulose, setose-ciliate, becoming dry but persistent. Leaf-stalks 2-6.5(-9) cm, at middle 0.4-1.1 mm diam., the ventral groove open and shallowly or scarcely depressed, often but not invariably spiculate at tip; pinnae 1-jug., the axis of each (5—)8—16(—21) mm, bearing the first of 2 pairs of lfts near or below middle, the anterior lft of this pair ovate-acuminate and much smaller than the rest; paraphyllidia lance-subulate 1-3.5 x 0.2-0.4 mm, strongly 1-nerved; lfts of distal pair dimidiately ovate or obliquely lance-elliptic to falcately lanceolate from semicordate base, 25-60 x (9-) 10-20 mm, 2-3.3 times as long as wide, at apex deltate- or triangular-mucronate or rarely obtuse apiculate, the thin-textured blades margined with a single continuous file of slender, forwardly appressed setae free through 0.4-1 mm, 3-5(-6)-nerved from setulose pulvinule, the secondary nerves from midrib incurved-ascending and either weakly brochid-odrome or sometimes expiring just short of margin, these and the sometimes obscure tertiary venulation sharply prominulous and pallid beneath, prominulous but not discolored above. Peduncles 1—3(—3.5) cm, either aculeate or unarmed; capitula without filaments 5-9.5 mm. diam., prior to anthesis either conelike or moriform; bracts linear or linear-oblanceolate, often (see key to vars.) setose-appendaged; flowers 4-merous 4-androus, a few lower ones smaller and staminate; calyx pappiform 0.7-1.6 mm, the tube 0.1-0.4 mm deep, ciliate with unequal pallid-stramineous paleaceous setae; corolla narrowly funnelform or subtubular 2.2-3 mm, 4-ribbed from base, the ovate acute, apically incurved but only a little thickened lobes 0.45-0.6 x 0.3-0.5 mm, either glabrous or puberulent externally, minutely ciliolate; filaments essentially free to base, pale pink or lilac-purple, exserted 5.5-7.5 mm. Pods (Lewis, 1987, fig. 9S) several or many per capitulum, sessile, in profile oblong or oblong-elliptic, rounded at each end but apically apiculate by a subulate beak 1-2.5 mm, when well fertilized 13-23 x 4-7 mm, the replum 0.4-0.6 mm wide, armed on dorsal and lateral ribs with stout straight erect, pallid or violaceous setae to 2.5-5 mm and commonly also minutely puberulent, the thin green, when ripe stramineous or brown, papery valves low-colliculate over each seed and also at least thinly setose, when ripe separating from replum and breaking up into 2-4(-5) indehiscent, free-falling articles 3.5-7 mm long; seeds olivaceous or fuscous-olivaceous 3-4 x 2-3.2 mm, the testa sublustrous.
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Discussion
Mimosa sensitiva is the common member of subser. Mimosa throughout northeastern Brazil, and readily known by the paleaceous-pappiform calyx, brochidodrome venulation of the relatively bright green leaflets, and northward from southern Bahia notable for the spinulose-marginate bracts that form a cancellately interlocking involucre around the flower-buds. Toward its southern limit in Bahia and Minas Gerais the species is, however, represented by the var. malitiosa, in which the bracts are much reduced in length and are almost or quite unappendaged, therefore exposing the flower-buds. This var. malitiosa suggests passage into the closely related M. velloziana, which has similar bracts but is nevertheless distinguished by a minute, naked or vestigially ciliolate calyx which coincides with a broader pod. While the faces of the pod of M. sensitiva are most often villosulous as well as setose and those of M. velloziana are ordinarily glabrous, this character is not as reliable as the literature would suggest.
Mimosa sensitiva, the type of its genus, was cultivated in northern Europe in the second half of the XVII century, very likely introduced from Pernambuco by Marcgrave or Piso. Its abrupt leaf-movements made it an object of wonder at that time, but as an exemplary sensitive it was soon replaced by the more easily grown and precociously flowering M. pudica.
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Distribution
Brazil South America| Bahia Brazil South America| Minas Gerais Brazil South America|