Mimosa pellita

Title

Mimosa pellita

Authors

Rupert C. Barneby

Scientific Name

Mimosa pellita Humb. & Bonpl. ex Willd.

Description

266. Mimosa pellita Humboldt & Bonpland ex Willdenow, Sp. pl. 4: 1037. 1805.—Typus infra sub var. pellita indicator.

Armed shrubs with ample microphyllidious sensitive lvs, usually of bushy round- or flat-topped outline, maturing at 1-3 m but potentially attaining 5 m with trunk 1 dm diam. and, not infrequently, when crowded at gallery-margin, sarmentose-scandent, exceptionally diffuse and trailing, variable in pubescence and armature, the stems, lf-stks and axes of inflorescence either strigose or hispid with forwardly appressed, ascending, or widely spreading, pallid or lutescent scaberulous setae to 1-3(-3.5) mm commonly mixed with minute puberulence, the stems and commonly also the dorsal or lateral ribs of lf-stks erratically armed with straight declined or with decurved or hooked, hornlike or broad-based aculei to 1.5-12 mm, the cauline aculei either infrastipular or intemodal, those of lf-stks either solitary or opposite on interpinnal segments, but either or both absent from some branches (or from some lvs of a branch), the many crowded olivaceous lfts subconcolorous brunnescent, either finely strigulose, finely villosulous, or glabrous except for margins at least remotely setulose-ciliolate, the globose or ellipsoid capitula solitary or 2-3 (-4) together in the axil of synchronously developing or hysteranthous lvs, often at first forming a shortly exserted pseudoraceme but quickly becoming axillary and immersed in foliage, the fruits (or empty repla) long persisting on annotinous branchlets and new fls often coeval with newly ripened pods. Stipules firm, ovate or lanceolate, ±2-5(-6) x 1-2 mm, externally densely silky-strigose, glabrous castaneous within, usually not visibly nerved externally and if so only distally and then not over 5-nerved, the blades becoming dry and brittle but normally persistent. Leaf-stalks of fully grown lvs (4-)6-20(-24) cm, the petiole including discolored pulvinus 3-16(-20) x 0.8-2.4 mm, the interpinnal segments 6-20(-22) mm, shallowly sulcate both ventrally and laterally, the ventral groove bridged and charged between pinna-pairs with a stiffly ascending, stramineous or brownish, glabrous or basally puberulent spicule (0.5-) 1.5—14(—23) mm; pinnae (6—)8—14(-l 6)-jug., either subequilong or proximally decrescent, the rachis of longer ones (2-)3-7(-8) cm, the longer interfoliolar segments mostly 0.6-1.2 mm; lfts of longer pinnae 25-44(-48)-jug., decrescent only at very ends of rachis, the first pair less than 1 mm distant from minute conic or subulate paraphyllidia, the blades linear from obtusangulate or shallowly blunt-auriculate base, acute or apiculate, those near mid-rachis 5-12 x 0.6-1.7(-2) mm, (5-)5.5-9(-10) times as long as wide, all smooth veinless above, beneath 4-5-nerved, the subcentric midrib and parallel lateral nerves all finely prominulous. Peduncles 1.5-7(-8) cm; capitula without filaments 8-12 x 6-9 mm, usually moriform prior to anthesis but bracts sometimes as long as the obtuse, scabrous-setulose fl-buds; bracts linear-oblanceolate 1-3.6 x 0.2-0.5 mm, 1- or 3-nerved, beyond middle either setulose, puberulent or glabrous dorsally, always setulose-ciliolate; flowers with paleaceous calyces, consisting of shallow brown campanulate cups 0.3-0.6 mm tall surmounted by four (sometimes unequal, asymmetric) lobes setose-decompound to variable depth, the whole 1-1.8 mm long; corolla 4(-5)-merous diplostemonous, narrowly turbinate, the ovate 1- or partly 2(-3)-nerved lobes 0.8-1.3 x 0.6-0.95 mm; filaments pale pink or lilac fading whitish, sometimes whitish from the first, united at base into a stemonozone ±0.5 mm, exserted 1.5-5 mm. Pods solitary or commonly 2-several, occasionally to 18 per capitulum, in profile linear or broad-linear, straight or slightly curved, 4—12(—13) x (0.6-)0.7-1.5 cm, abruptly contracted at base into a stout stipe 1- 5(-7) mm, broadly rounded and abruptly cuspidulate at apex, either piano-compressed or compressed but turgid, the replum 0.6-1.2 mm wide, the brownish-green, reddish-brown or livid, either thinly or stiffly chartaceous valves either setose with erect, variably broad-based and variably crowded or distant setae to 2-4.5 (-6) mm and sometimes in addition minutely puberulent, less commonly shortly and sparely strigose with finer tapering, forwardly ascending or appressed setae to ±2 mm, when ripe breaking into 14-21 (-24) or exceptionally only 8-13 (or by abortion of ovules fewer) free-falling articles, those near mid-pod 2.5-4.5 mm long (hence ±2-4 times broader than long), that at each end of pod longer, all either individually indehiscent, closed at each end by a septum 0.2-2 mm wide, or dehiscent and not or only very narrowly membranous-septate, the seeds consequently shed, as the case may be, either encapsulated (when readily water-borne) or naked (when instantly submersible); seeds transverse, narrowly compressed-oblong-ellipsoid ±4.5-6 x 2-2.6 mm, the smooth testa olivaceous or brown-olivaceous dull.

Mimosa pellita, as described above, is equivalent in essence, though not in all details, to M. asperata of Bentham’s revision (1875: 437) and to M. pigra of most modem floras, but appears here under an unfamiliar name. Study of the types of the two Linnaean names that have prevailed in the literature has shown (Barneby, 1989) that neither can be applied, sensu stricto, to this commonest of all shrubby mimosas, but that each properly belongs to a close relative of relatively narrow range, M. pigra to the species that has passed in Argentina as M. vellosiella Herter, and M. asperata to the northern segregate M. berlandieri. Only by combining all these into one polymorphic taxonomic artifact could M. pigra, historically the oldest name for any member of the group, be preserved in the sense of recent authors.

Even when the peripheral microspecies M. asperata (=M. berlandieri), M. elliptica Benth, and M. pigra (sens. str.) are isolated, the residue of Bentham’s "Asperatae verae" presents an initially dismaying array of variation in pubescence, in armature, in dimensions and form of stipules and fruits, and in other characters. Analysis reveals, however, that all is not random or chaotic, but on the contrary subject to order and related to dispersal. Close attention to attachment of cauline setae, to form and venation of stipules and floral bracts, to dehiscence of the fruit and release of the seeds has revealed unsuspected specific and varietal entities described herein as M. orinocoensis, M. tarda, and M. pellita vars. dehiscens and hispida, the last described at the same time as M. pellita itself but never correctly characterized. Pruned of these discordant elements, M. pellita yet remains the most widely dispersed shmbby mimosa, extending autochthonously in typical form from tropical lowland Mexico to northeastern Argentina, over much of Antillea, over most of tropical Africa, and as a colonist further afield in Malesia and Australia.

Within its immediate group M. pellita is recognized by small, firm, dorsally silky-strigose stipules usually not perceptibly venulose, or if weakly so, with major nerves five or less in number. The pod takes two forms. In one the individual one-seeded articles fall from the replum indehisced, sealed at each end by a persistent septum of variable width; in the other each article dehisces independently into free-falling panels. In the first case each seed is dispersed in a buoyant envelope and can be borne on water far from the parent plant; in the second it is shed naked, to sink directly into mud or water. Pods of the first type tend to be tumid when ripe and densely hispid with stiff crowded perpendicular setae, whereas those of the second type are piano-compressed and more weakly pilose or strigose with more scattered, ascending or subappressed setae, the difference often, but not invariably, becoming evident before maturation of the fruit. The dehiscent type, which closely simulates related M. tarda, is dispersed in a broad crescent around the southern periphery of the Amazon basin, sometimes associated with the indehiscent type. It is not known to occur in North America or in the Old World, but it may be cryptically present, for plants collected in flower only cannot be distinguished. A variant local in northern Venezuela notable for narrow pod and small, proportionately broad seeds may be recognized as var. hispida.