MIMOSA

Title

MIMOSA

Authors

Rupert C. Barneby

Scientific Name

Mimosa

Description

MIMOSA

Mimosa Linnaeus, Sp. pl. 516. 1753 & Gen. pl. ed. 5, 233. 1754; emend. Bentham, J. Bot. (Hooker) 4: 358. 1841, in Bentham & Hooker, Gen. pl. 1(2): 593. 1865; Trans. Linn. Soc. London 30: 388. 1875. —Sp. lectotypica (Britton & Wilson, Sci. Surv. Porto Rico & Virgin Is. 5(3): 357. 1924, confirmed by Britton & Killip, Ann. New York Acad. Sci. 35: 149. 1936, and by Farr & al., Index nom. generic. 2: 1097. 1979): M. sensitiva Linnaeus.—An alternative lectogeneritypus, M. pudica Linnaeus, proposed by Hitchcock & Green, Proposals Brit. bot. 162. 1929, is rejected as posterior.

Essential characters. Stamens as many or twice as many as corolla-lobes, the filaments either free, or basally adherent to corolla to form a shallow stemonozone, or shortly monadelphous, the anther-connective in dorsal view round or broadly ovate, girdled or almost so by the sacs, lacking a terminal gland; fruit a planocompressed or turgid pod, with continuous replum (margo) corresponding with the sutures, the valves at maturity either continuous and therefore separating from replum, either along both sides or primarily from apex downward, in one piece, or (more frequently) articulate into free-falling 1-seeded articles, then termed a craspedium; seed-testa bearing on each face a ± hippocrepiform pleurogram (linea fissuralis); endosperm present.

Description. Trees, shrubs, vines, subshrubs (a few acaulescent), herbs (erect or humifuse), a few of the latter monocarpic; stems either a) unarmed, or b) armed at or below each node, either on infrastipular or infrapetiolar ribs, with few, commonly 1-3, either straight, recurved, or rarely antrorse aculei, or c) serially armed on several or all ribs of each intemode with files of recurved (cat’s-claw) aculei, these sometimes extending to the lf-axes, and sometimes d) in addition or alternatively, hispid with stiff setaculei intermediate in form and stiffness between setae and aculei. Indumentum composed in various measure and in random combination of: a) minute incurved puberulence, b) short plain hairs, c) short clavate or granular, commonly orange or livid, non-secretory trichomes, d) filiform set(ul)ae, e) tapering or flagelliform setae broadest or bulbously dilated at base, these sometimes laterally attached and seemingly calcarate, f) setae (especially cilia of lfts) produced backward into the epidermis, g) scabrous or arborescently plumose setae becoming, by shortening of the primary axis, stelliform, h) gland-tipped (secretory) set(ul)ae, or i) in sect. Mimadenia only, sessile or stalked, peltate or squamiform trichomes; exceptionally the whole plant glabrous or the indumentum rudimentary, the plain setae when present variably oriented. Stipules setiform, lanceolate, ligulate, or dilated, then many-nerved externally or the nervation immersed, the blades commonly persistent, sometimes becoming dry and fragile. Lvs (except of M. unipinnata) bipinnate, the primary and secondary axes normally pulvinate (the primary pulvinus rarely suppressed), the lfts sessile, the first pair of each pinna commonly differentiated into paraphyllidia (stipels of Bentham), the pairs of pinnae and the lfts folded forward at night and often abruptly so by day following shock or touch and the petiole simultaneously refracted (but in some spp. all inert); lf-stk sulcate ventrally, the sulcus often bridged between pinna-pairs and not rarely charged with an ascending spicule (also formerly called a stipel), in sect. Mimadenia alone the lf- stk with one or more cupular or mounded (flaskshaped) secretory nectaries; lf-formula highly diverse, the pinnae and the lfts one to many pairs, the number and size commonly reciprocally adjusted; venation of lfts basically palmate from pulvinule, the primary nerves sometimes immersed, sometimes elaborately branched and distally anastomosing, a pallid or callous marginal nerve developed in some species-groups. Inflorescence composed of spikes (racemes) or capitula, these solitary or fasciculate either in the axil of contemporary lvs or gathered into terminal, simple pseudoracemes or branched panicles, in some xeromorphic spp. fasciculate on hemispherical brachyblasts along annotinous branches, in a few acaulescent subshrubs the peduncles radical scapiform; bracts either shorter than or enclosing the fl-buds, the capitulum shortly before anthesis termed in the first case moriform (resembling a Morus syncarp), in the latter conelike, the bracts either deciduous or persistent; bracteoles 0; fls either sessile or (less often) shortly pedicellate, 3-5(-6)-merous, either all haplostemonous, or all diplostemonous and then either all hermaphrodite or some lower ones of a unit of inflorescence (rarely all) functionally staminate with rudimentary gynoecium or exclusively staminate, in few spp. of sect. Mimosa the upper fls haplostemonous hermaphrodite and some lower ones staminate diplostemonous; calyx campanulate, or reduced to a shallow saucer, or even obsolete, the orifice either truncate, or denticulate, or lobed, the lobes in some paleaceous and cleft to variable depth, when deeply cleft becoming pappiform; corolla-lobes united into a tube commonly as long as or longer than, exceptionally shorter than, the free blades, these either plane or cymbiform, 1-several-nerved; filaments pink-purple, pink fading whitish, white, or (sect. Calothamnos) ochroleucous to bright sulfur-yellow, ordinarily 2-several times as long as corolla; pollen grains united into simple, double, or triple tetrads. Fruit as described above, either sessile or stipitate, the valves often colliculate or bullate over each seed, the cavity either continuous or commonly closed between successive seeds, sometimes by a hyaline partition, the replum and valves either separately or together glabrous to puberulent, setose, glandular- setose or aculeate (the indumentum independent of that of stems or foliage); seed-funicle elongate filiform; seeds either transverse to the vertical axis of pod, or obliquely basipetal, or vertically basipetal, mostly compressed-ovoid and uni-seriate but sometimes deformed or disoriented by crowding; germination epigeal.

Spp. ± 480 of which 461 are native to the New World, most numerous and diverse within the tropics at low and middle elevations, a few extending n. into temperate centr. United States and s. into temperate Argentina, few native American but widely naturalized or casually weedy in the paleotropics (one or two, M. pellita, M. pudica, perhaps naturally circumtropical but also opportunistically weedy), few native in tropical Africa and s. Asia, about a dozen endemic to Madagascar; ranging in habitat from macro-thermic equatorial forest to lowland savanna and campo habitats, tropical and subtropical thom-forest and scrub woodland, tropical-montane brush-woodland, temperate grassland, and desert, readily adapting in growth-form to these environments; chief foci of speciation in a) Brazil s. of Amazonia and adj. Paraguay, Argentina, and Uruguay, and b) in centr. and s. Mexico, minor ones in Cuba-Hispaniola, the Orinoco basin, and Madagascar.