Mimosa diplotricha

  • Title

    Mimosa diplotricha

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Mimosa diplotricha C.Wright ex Sauvalle

  • Description

    120. Mimosa diplotricha C. Wright ex Sauvalle, Anales Acad. Ci. Méd.Habana 5: 405. 1868. —Typus infra sub var. diplotricha indicatur.

    Herbs and subshrubs of rapid growth and early maturity, when young often appearing monocarpic but potentially soft-woody in age, the diffuse, ascending or (when crowded) leaning and scrambling, pith-filled stems (0.5-) 1-2.5 m, usually densely, sometimes remotely armed along the (4-) 5 continuously prominulous stramineous ribs with sharp recurved, stramineous brown-tipped aculei to (1—) 1.5—3(—3.5) mm and usually also ± villosulous with fine erect-spreading hairs to 0.3-1 (-1.3) mm, exceptionally glabrous, the dorsal rib of lf-stks and axes of inflorescence similarly prickly, the bicolored, dorsally pallid, thin-textured lfts from villosulous on both faces to minutely ciliolate but facially glabrous, exceptionally glabrous overall, the short-pedunculate globose capitula at first axillary and much surpassed by the subtending lf, some later ones becoming pseudoracemose. Stipules narrowly lance-attenuate or setiform, sometimes a little dilated at base, 2-6(-7) x 0.25-0.6 mm, often reddish, 1-nerved dorsally, sometimes subtended by a pair of prickles, persistent. Leafstalks of primary cauline lvs (4-)5-10.5(-12) cm, the petiole (1.5-)2.5-7 cm, commonly about as long as or longer than the rachis, this 2-5.5 cm, its longer interpinnal segments (3-)4-8(-10) mm, the ventral groove interrupted between pinna-pairs by an erect-ascending spicule; pinnae of middle lvs or of all lvs below inflorescence 4-8(-9)-jug., very sensitive and in most herbarium specimens deflected and folded back-to-back behind lf-stk, the rachis of longer ones 1.5-3.5(-4) cm, the longer interfoliolar segments 0.5-1.6(-2) mm; lfts of longer pinnae 17-28-jug., the first pair 0.3-2 mm distant from unequal paraphyllidia, the exterior member of these 0.6-1.6, rarely 2.5 mm, the lft-blades in outline linear-oblong or linear, subacute or apiculate, those near mid-rachis 2.5-6(- 7) x 0.6-1.2(-1.4) mm, 4-5.5 times as long as wide, all veinless above, beneath faintly l(-2)- nerved from pulvinule, the subcentric midrib very slender, often merely discolored, the posterior nerve when present short or obscure. Peduncles 1-3 per node, commonly geminate, 5-16(-20) mm; capitula without filaments 4-5.5(-6) mm diam., prior to anthesis moriform; bracts elliptic-oblanceolate 0.4-1 mm; flowers normally 4-, rarely and randomly 5-merous, diplostemonous, either all bisexual or a few lower ones staminate; calyx campanulate 0.2-0.4 mm, glabrous, the rim entire or obscurely denticulate; corolla narrowly turbinate or vase-shaped 1.7-2.4(-2.8) mm, the membranous ovate concave 1-nerved, reddish or sometimes green lobes 0.5-0.9(-1) x 0.4-0.65 mm, either glabrous or thinly hispidulous externally; filaments pink, very shortly or obscurely monadelphous around base of ovary, exserted (2—)3—5 mm. Pods usually 10 or more per capitulum, crowded into a dense umbelliform cluster close against the stem, sessile, in profile oblong or linear, straight or gently decurved, usually (8-)10-24(-35) x 3_4.2(-5.5) mm and (2-)3-8- seeded but in Mexican var. odibilis 40-70 mm long and 12-16-seeded, the replum 0.4-0.6 mm wide, densely (sparsely) aculeate along dorsal and lateral ribs with either erect or decurved prickles 0.4-1.3 mm, the papery valves usually villosulous and either overall or only over each seed ± densely setaculeate, sometimes simply setaculeate, when ripe breaking into free-falling, individually dehiscent, rhombic or almost square articles 3-3.5 mm long; seeds compressed, in broad profile rhombic or ovate 2.3-3 x 1.4-2 mm, the testa pale or rich brown, lustrous.

    In the context of its immediate group, diagnostic characters of M. diplotricha are relatively long leaf-petioles coinciding with very short axillary peduncles, 4-8 pairs of pinnae crowded along an axis no longer, often shorter than the associated petiole, and the fertility of most flowers of each capitulum, the pods forming a dense umbellate cluster. Varieties of M. quadrivalvis, similar in prickly stem and shortly pedunculate capitula, are easily mistaken for M. diplotricha before the characteristic fruits begin to take form; but the common South American element of this group, M. quadrivalvis var. leptocarpa, may be known even at anthesis by relatively few (2-4, not 4-9) pairs of pinnae in largest leaves, and the less widespread var. tetragona by petioles shorter (not longer) than leaf-rachis. Rare forms of M. diplotricha with only few and scattered prickles resemble M. gracilis var. invisiformis, endemic to highland east-central Goiás, but in this each capitulum bears only one or two fertile fruits. Other close relatives are: M. supravisa, which has fewer broader leaflets and longer pods with simply villosulous (not setose) valves; M. selloi, with subterete rather than sharply pentagonal stems, only 2-4 pairs of pinnae per leaf, and stipitate pods; and M. suburbana, like the last but with trigonous stems. In North America and the Antilles, where M. diplotricha may not be primitively indigenous, it has only one close native relative, M. pinetorum, with only one pair of pinnae per leaf. Care must be taken, however, to distinguish M. diplotricha from Mexican and Central American members of ser. Quadrivalves, for which fruits at least in formative stages are almost indispensable.

    Mimosa diplotricha is an invasive, prolific, fast-growing, and with few exceptions formidably prickly weed, rich in minor variations of stature, leaf-formula, pubescence, and armament. All its common forms are serially armed along the ribs of stem and leaf-stalk with sharp cat’s-claw aculei, but occasional individuals (e.g., Schunke 1115 from Huanuco, Peru, NY) show only a few scattered cauline prickles and unarmed leaf-stalks. A completely unarmed form (M. invisa fma inermis Adelb.), first noted in Papua New Guinea, is now cultivated for cover and forage in the East Indies and tropical Africa, and is the subject of agronomic studies and breeding programs. Notable Brazilian variants are represented by Hatschbach 34279 from Goiás (NY), which has peduncles to 20 (not 5-14) mm long, and by W. R. Anderson 8803 from Minas Gerais (NY), with abnormally stout pods attaining 32 x 5.5 mm. An outstanding Mexican form with pods twice as long and seeds twice as many as in normal M. diplotricha is described below as var. odibilis.