Mimosa nuda

Title

Mimosa nuda

Authors

Rupert C. Barneby

Scientific Name

Mimosa nuda Benth.

Description

328. Mimosa nuda Bentham, J. Bot. (Hooker) 4: 362. 1841.—Typus infra sub var. nuda indicator.

Functionally herbaceous subshrubs from a xylopodium or knotty root-crown surmounting 1 or more, slenderly fusiform woody roots, the stems weakly procumbent, assurgent, virgately erect, or rarely (when crowded) sarmentose, at maturity (2-)4-14(-17) dm tall, either (commonly) unarmed or the subterete intemodes with a few random recurved aculei 0.5-2 mm, in all parts variable in indumentum, the stems either a) hispidulous with weak spreading sordid setae less than 1 mm mixed or not with minute puberulence and sometimes in addition minutely granular, or b) more coarsely hispid with erect rufescent setae to 1—3(—5) mm mixed or not with puberulence, or c) fully glabrous, the ordinarily ample lfts, either beneath or on both faces, either a) ascending-setose and finely pilosulous, or b) simply ascending-setose, or c) simply pilosulous, or d) glabrous overall or only on those surfaces concealed in attitude of sleep, the continuous, often shallowly crenate, corneous margin of blades with either uniseriate or more numerous pluriseriate, forwardly appressed setae 0.5-2 mm, or (less often) esetose smooth, the faces of lfts bicolored, when dry brown and sometimes glaucescent above, paler brown beneath, the globose or subglobose capitula l-2(-3)-nate in distal lf-axils and forming, in early to late anthesis, a simple or few-branched pseudoraceme exserted (0.5-)l-2 dm beyond expanded lvs, the stems and foliage alike often exuding when cut a pallid latex. Stipules erect firm, lanceolate or lance-attenuate (2—)4—11 x 0.6-1.8 mm, coarsely 3-5- nerved, either glabrous or setulose dorsally, glabrous within, except in var. nuda pectinately ciliate, persistent. Leaf-stalks (1.5-)2-9(-l 1) cm, widely shallowly sulcate ventrally, at middle 0.5-1.4 mm diam., at very base comeously thickened next to livid wrinkled pulvinus, espiculate at apex; rachis (including pulvinus) of the single pair of pinnae (5-)7-20 mm, the shorter first pair of lfts a little below middle, the paraphyllidia linear-lanceolate or narrowly ovate (0.5-) 1-4(-5) x 0.2-0.8 mm; lfts 2-jug., the distal pair larger, the anterior lft of proximal pair reduced to a para-phyllidium or very small ovate-acuminate blade, the distal lfts in outline obliquely obovate, oblong-obovate or lunately broad-elliptic to narrowly oblong or linear, consequently widest near or beyond mid-blade, all semicordate at base, commonly obtuse but abmptly apiculate or mucronate, those of ampler lvs (11-20-)25-94 x 3-30(-36) mm, 1.8-5 times as long as wide, 3-5-nerved from pulvinus, the ± excentric midrib giving rise on each side to 4-8 secondary nerves anastomosing with the continuous marginal nerve, the venation dorsally discolored and prominulous, ventrally less so or fully immersed. Peduncles (9-) 12-45(-80) mm; capitula 5-7 mm diam. without filaments, prior to anthesis moriform or hispid with shortly projecting bracts, these linear or linear-attenuate 1-3 x 0.2-0.6 mm, glabrous and stongly carinate dorsally, commonly pectinately ciliolate but the cilia sometimes suppressed; fl-buds obovoid, nearly always glabrous; flowers 4-merous 4-androus, some or many lower ones of any capitulum staminate; calyx 0.2-0.3 mm; corolla narrowly vaseshaped (2-)2.3-3.5 mm, the ovate, concave but not strongly cucullate, prominently carinate lobes 0.6-1.2 x 0.5-0.7 mm; filaments free or obscurely united into a stemonozone below the ovary, distally pink or rose-purple sometimes fading whitish, exserted 6.5-9.5 mm. Pods ±320 per capitulum, sessile, piano-compressed, in profile linear or (when short) ovate-oblong or lance-acuminate (7-)l 1-24 x 4-5.5 mm, at apex triangular or acuminate, the shallowly undulate or straight replum 0.5-1 mm wide, the papery valves low-colliculate over 2-5(-6) seeds, when fully ripe brown lustrous, subresinous or pruinose, either separating entire from replum or erratically fissured transversely (especially near replum) into articles 3-5 mm long, the replum and valves alike hispid overall with erect yellow setae to 1-3 mm (and rarely in addition puberulent-pilosulous), or the replum alone hispid and the valves smooth, or (var. nuda) smooth overall; seeds ±3.5-4 x 2.5-3 mm, plumply compressed-obovoid, sometimes subcarinate around long circumference, the testa lustrous brown.

The complex series of forms here assembled under the title of M. nuda appear collectively to represent progressive adaptations of an ancestral "Sensitiva" resembling M. debilis to campo and cerrado habitats on the Brazilian Planalto and in floristically related parts of Bolivia, Paraguay and Argentina. They exhibit modifications characteristic of functionally herbaceous subshrubs adapted to a hot dry season and intermittent campo fires: woody roots or xylopods; stems renewed annually from the ground but varying in attitude from humifuse to erect and wandlike, but even when crowded only incipiently sarmentose; sclerosis of leaf-blades and stiffening of their venation; and loss of aculei along with loss of sarmentose growth-form. In progressive narrowing of the leaflet-blades and in progressive loss of hispid or villosulous indumentum, the variation in M. nuda follows paths parallel to those described for M. debilis. The whole range of leaflet shape encountered in M. nuda as defined herein is wider than in all other members of subser. Mimosa combined and, as the pubescence of leaves and pods is independently labile, the combinations of actually-observed and potential character-states are seemingly endless. One looks vainly for differential characters in the flower and the pod, for these are as uniform in size and structure as those of M. debilis. Bentham proposed within the megaspecies M. nuda four specific and one varietal taxa, each of them based on a single collection that displayed a particular syndrome of characters in the foliage, indumentum, or both. These now can be seen as random selections from a then unforeseeable pool of minor variants.

In these circumstances exact definitions of M. nuda and its varieties cannot be expected, and a distinction between a glabrous "M. obtusifolia" and a pubescent "M. rixosa" proposed by Burkart (1948: 211, 214) for Argentina populations of M. nuda is impossible to maintain in Paraguay or Brazil. The key that follows makes no provision for troublesome intermediate forms already known or for others surely to be expected.

During several years of study leading to this account of M. nuda I have found myself passing from one alternative taxonomy to another without finding satisfaction in any. At a time when I was still unaware that M. glaucescens Bentham was a posterior homonym, I used, in annotation of specimens that long ago passed out of my hands, several unpublished trinomials based on this name.