Mimosa distans

Title

Mimosa distans

Authors

Rupert C. Barneby

Scientific Name

Mimosa distans Benth.

Description

462. Mimosa distans Bentham, J. Bot. (Hooker) 4: 382. 1841.—Typus infra sub var. distanti indicatur.

Unarmed subshrubs and suffruticose herbs (1.5—)3—11(—15) dm, the commonly stiff but slender, either erect or incurved-assurgent, but at times pliantly prostrate, either simple or distantly few-branched stems (1-) 1.5-4 mm diam. and often glabrescent proximally, upward openly or remotely, less often densely foliate and, like lf-stks and peduncles, either strigose or hispid with tapering, sometimes flagelliform setae to 1-3 mm, these forwardly appressed to spreading, loosely deflexed, or retrorse, the dull or sublustrous olivaceous foliage subconcolorous, the firm or subcoriaceous lfts glabrous on upper face, beneath usually finely, thinly, or remotely villosulous (especially on side posterior to midrib) but sometimes quite glabrous, the proximal ones commonly setose dorsally, all either finely or grossly setose-marginate, the peduncles all or mostly axillary to distal lvs or some forming an efoliate pseudoraceme exserted to 1 dm beyond foliage. Stipules firm, lanceolate or lance-ovate 3-9 x (0.5-)0.75-2 mm, coarsely 3-7-nerved, dorsally glabrous, puberulent or setose, glabrous within, either persistent or tardily deciduous. Leaf-formula variable especially in number of pinnae, the lf-stks 0.5-6(-8) cm, at middle 0.4-0.8 mm diam., shallowly sulcate ventrally, espiculate, the petiole commonly 0.5-3.5, in var. neuroloma only 0.15-0.4 cm, in var. paraguariae to 6.5 cm, the interpinnal segments, when present, 2-10 mm; pinnae exactly 1-, 1-2-, 2-5-, 4-8-jug., when 2-jug. or more either distally accrescent or irregularly graduated, the rachis of longer ones 2.5-9.5 cm, the interfoliolar segments 1.2-3.5 mm; lfts of longer pinnae commonly 15-40-. rarely only 11-15-jug., a little decrescent at each end of rachis, the first pair 0.6-1.7 mm distant from subulate paraphyllidia 0.5-2 mm, all in outline obliquely lanceolate or lance-oblong, acute or abruptly apiculate, broadest at obtusangulate base, the larger ones 7-17 x l.2-4(-5.5) mm, 2.8-5(-5.5) times as long as wide, all 3-5-nerved from pulvinule, the dorsally stout and pallid midrib displaced to divide blade 1:2.5-5, the posterior nerves weaker, the inner one incurved- ascending 1/3-2/3 length of blade, the exterior ones shorter, the continuous or subcontinuous series of marginal setae variable in girth, their tips free for 0.7-1.7 mm and usually appressed or narrowly ascending, rarely patent. Peduncles 2-6.5 (-7.5) cm, solitary at some early nodes but mostly 2-3-nate distally; capitula globose or plumply ellipsoid, without filaments 6-7 mm diam., prior to anthesis moriform, the obovoid 4-keeled fl-buds densely gray- or silvery-strigulose between the keels with retrorsely subappressed hairs; bracts linear-oblanceolate 0.8-2 mm, dorsally glabrous and prominently carinate, thinly setose-ciliolate distally; flowers 4-merous 4-androus, some proximal ones staminate and shorter; calyx membranous 0.15-0.25 mm, the truncate or obscurely lobulate rim either glabrous or minutely ciliolate; corollas 2-3.2 mm, the shorter ones narrowly turbinate, the longer funnelform-subcylindric, the firm but not corneous cymbiform lobes 0.6-1.1 x 0.4-0.6 mm; filaments pink, free to base, exserted 4.5-8 mm. Pods ±2-20 per capitulum, sessile or contracted at base into an obscure stipe less than 1 mm, the narrowly oblong body (8-) 10-18 x 3-4 mm, undulately constricted at isthmi between 2-5 (-6) seeds, the replum 0.3-0.5 mm wide, hispid along back and sides with erect, microscopically scaberulous setae 0.6-1.5 mm, the ripe valves papery brownish-stramineous, densely strigose-hispidulous with appressed or subappressed retrorse setae a little shorter than those of replum, when ripe breaking up into free-falling indehiscent biconvex articles 2.5-4 mm long; seeds plumply lenticular 2-2.8 x 1.7-2.5 mm, the testa either fuscous or pale yellow-brown, smooth.

Here assembled under the collective name M. distans will be found elements derived from two Benthamian series of Eumimosa: from ser. Pedunculosae, M. elongata and M. distans; and from ser. Meticulosae, M. neuroloma. Bentham separated these species by inconstant characters of pinna-number and by strength of setae that run together to form a pallid marginal nerve of variable girth. But these and others subsequently discovered are essentially identical in morphology of the flower and fruit, and have in common a distinctive subdimidiate leaflet and retrostrigulose corolla.

The constituent varieties of M. distans are conveniently divided by leaf-formula into a subsp. elongata, in which the pinnae vary in number from one to two, two to five, or four to eight pairs, and a subsp. distans, in which the pinnae are stabilized at exactly one pair. The latter is widely dispersed, in the form of var. distans, over much of the Brazilian Planalto, and is represented in the central highlands by a relatively rare var. neuroloma. The subsp. elongata is composed of several, more local, varieties concentrated in central Goiás and the Federal District but has an outlying member in Paraguay. This pattern of dispersal is comparable, on a more modest scale, to that described for M. somnians: one widespread subspecies, ostensibly primitive relative to the rest, containing within its compass increasingly specialized and geographically restricted derivatives. If this hypothesis is correct, the varieties of M. distans with plurijugate leaves have arisen from conjugately pinnate ancestry.