Mimosa polydactyla

Diffuse, ascending or sometimes scrambling, in age suffrutescent, microphyllidious herbs (2-)5- 16(-20) dm, the terete stramineous or reddish-brown stems armed at or shortly below each node with a pair of stout recurved broad-based brown-tipped aculei 1.5-5 mm and often also with l(-2) similar infrapetiolar ones variably displaced downward, the cauline and foliar axes thinly hispid or strigose with either erect, ascending, or less often forwardly subappressed, stiff but slender, brown or brown-tipped setae to 1-2.3 mm mixed or not with fine puberulence, the sensitive subpalmately pinnate lvs olivaceous bicolored, the narrow plane thin-textured lfts a little paler beneath, commonly glabrous facially and forwardly setose-ciliate, sometimes dorsally appressed-setose-silky, the small ovoid-ellipsoid capitula either solitary or paired, rarely to 4 together, in a long succession of lf-axils, on peduncle shorter than subtending lf-stk. Stipules erect, linear-attenuate or subsetiform 4-8 x 0.25-0.6 mm, 1-nerved dorsally, pectinately setose-ciliate, persistent. Leaf-stalks (1.5-)2-6(-7) cm, the petiole including elongate discolored pulvinus 1.5-5.5(-6.5) cm, grooved both ventrally and laterally, at middle 0.6-1.1 mm diam., the 2-4 interpinnal segments commonly 1-2 mm, sometimes almost 0; spicules 0; pinnae 3-5-jug. (of some early lvs 2-jug., no further described), ordinarily accrescent distally but sometimes equilong, the rachis of longer ones 4— 10(— 11) cm, the interfoliolar segments 1-2 mm; lfts of longer pinnae (28-)30-55(-65)-jug., decrescent at each end of rachis, the first pair 0.7-2.3 mm distant from linear-subulate paraphyllidia 0.5-1.4 mm, all in outline linear-acute from semicordate base, straight or nearly so, those near mid-rachis (4-)5-9 x (0.6-)0.8-1.8 mm, 5.5-7.5 times as long as wide, all veinless above, beneath 2-3-nerved from pulvinule, the subcentric prominulous pallid midrib weakly 2-4-branched mostly beyond middle, the adjacent posterior nerve scarcely attaining mid-blade, the outer posterior one very short or obsolescent. Peduncles 7-15 mm; capitula without filaments 3-4 mm diam., prior to anthesis moriform, but hispid with emergent bracteal setae; bracts linear or linear-elliptic 0.71 x 0.15-0.25 mm, 1-nerved, charged on each margin distally with 2-3 pallid ascending setae; flowers 4-merous 4-androus, usually all bisexual and fertile; calyx submembranous 0.2-0.4 mm, glabrous externally, the irregularly or obscurely lobulate rim sometimes minutely setulose; corolla submembranous, narrowly vase-shaped 1.1-1.7 mm, the almost plane, dorsally low-carinate lobes 0.45-0.7 x 0.3-0.5 mm, externally either glabrous or minutely hispidulous; filaments pale pink or whitish, obscurely monadelphous at very base, exserted ±2-2.5 mm. Pods radiating from receptacle in dense spherical clusters, subsessile, the body of each in profile narrowly oblong 915 x 3.5-4.5 mm, (2-)3—4-seeded, the undulately constricted replum 0.2-0.4 mm wide, contracted at apex into an erect cusp, with divaricate straight tapering stramineous or livid setae to 24 mm along lateral and dorsal ribs, the papery greenish-brown, when ripe brown or blackish valves also thinly or randomly setose and sometimes in addition microscopically puberulent, breaking up when ripe into free-falling biconvex, individually indehiscent articles ±2.5-3.5 mm long; seeds lentiform 2.3-2.8 x ± 2 mm, the testa olive-drab or reddish-fawn, under magnification x 30 minutely roughened.

A weedy mimosa of disturbed forest, brush-woodland, pasture thickets, hedgerows and ditch- banks mostly below 350 m, but attaining 1000 m in Ecuador and s.-e. Brazil, interruptedly widespread in the Amazon Basin from s.-w. Venezuela and e. Colombia to n.-e. Peru, and e. in Brazil to Pará, thence n.-w. in scattered stations to the Pacific slope in Colombia (Chocó) and Central America (Panama and Costa Rica), and n.-e., mostly along and near the Atlantic seaboard, less commonly inland, through the three Guianas to the Guayana Highland in Bolívar and Delta-Amacuro, Venezuela, and s.-e. in Brazil to central Minas Gerais and the Organ Mts. in Rio de Janeiro; Martinique; naturalized in equatorial w. Africa (Ilha S. Tome fide Exell, Vase. Pl. S. Tomé 169. 1944).—Fl. throughout the year except when drought-inhibited. Map 60.

Mimosa polydactyla is evidently most closely related to M. pudica, which it resembles in its weedy, weakly suffrutescent habit of growth, in subpalmately pinnate leaves, in relatively simple leaflet-venation, and in much reduced calyx, all advanced characters in the genus. The differences between them in leaf-formula, while usually instantly apparent in mature specimens, are not individually absolute. Some leaves of each may have just three pairs of pinnae, and some pinnae of each may have about thirty pairs of leaflets. However, when pinnae of most leaves are three pairs the leaflet-number is decisive and when leaflet-number is ambiguous the number of pinnae is decisive. Only quite immature or incomplete specimens present any problems in identification. Mimosa verecunda, similar in leaf- formula, has pinnae more openly spaced along the upper leaf-stalk in most leaves, but is most reliably distinguished by the paleaceous-pappiform calyx, and most readily so by allopatric (upland planaltine) distribution.