Mimosa leptorachis

  • Title

    Mimosa leptorachis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Mimosa leptorhachis Benth.

  • Description

    281. Mimosa leptorachis Bentham, Trans. Linn. Soc. London 30: 434. 1875 & in Martius, Fl. bras. 15(2): 376, descr. ampliat. 1876.—"Habitat inter arbusta in deserto Frio versus flumen S.Francisco, provinciae Minas Geraës: Martius."—Holotypus, M (3 sheets)! one = F Neg. 6189.

    Slender unarmed, diffusely branched shrubs of unknown stature, glabrous except for very few random gland-tipped trichomes less than 0.2 mm on some young flowering branchlets, the stems smooth lustrous purplish-brown, the lvs brown-olivaceous concolorous when dry, the small globose capitula solitary or rarely geminate in lf-axils of all distal branchlets, together forming an open leafy panicle. Stipules firm livid, narrowly ovate 1-2 mm, obscurely several-nerved, persistent. Leaf-stalks very slender subterete 1.5-4.5 cm, the petiole 7-24 mm, at middle 0.2-0.25 mm diam., the longer interpinnal segments 3-5.5 mm, the ventral groove interrupted between each pinna-pair by a spicule 0.25-0.5 mm; pinnae 3-6-jug., slightly decrescent proximally, the rachis of distal ones 3-6(-7) mm, the interfoliolar segments 0.6-1 mm; lfts of distal pinnae 5-9- jug., a little decrescent at each end of rachis, the first pair 0.7-1 mm distant from subulate paraphyllidia 0.1-0.2 mm, all in outline narrowly oblong-oblanceolate from abruptly angulate base, broadly obtuse, those near mid-rachis 3-4.5 x 0.7-1.3 mm, ±3-4 times as long as wide, the firm plane blades 3(-4)-nerved from pulvinule, the distally subcentric midrib pinnately 2-branched on each side, the venation bluntly prominulous pallid beneath, scarcely perceptible above. Peduncles 11-15 mm; capitula without filaments 4.5-5 mm diam., prior to anthesis moriform; bracts submembranous elliptic-obovate 0.4-0.6 mm; flowers 4-merous 8-androus, some proximal ones smaller and staminate; calyx membranous campanulate 0.3 mm, the rim microscopically erose; bisexual corollas turbinate-campanulate ±2.1 mm, the firm, striately several-nerved, shallowly concave lobes ±1.2 x 0.75 mm; filaments free, presumably pink, exserted 5-6 mm; ovary at anthesis glabrous; pod unknown.

    Reported from shrub thickets, presumably in cerrado climax, to be sought on the crest and w. slope of Sa. do Espinhaço in n.-centr. Minas Gerais, Brazil.—F. VII-VIII(-?).

    Mimosa leptorachis, collected once in 1818 and not since seen, is a small satellite or derivative of polymorphic M. somnians and different from all forms of it in short paucifoliolate pinnae. Bahian M. glaucula approaches it in leaflet-number, but has only two pairs of pinnae per leaf and is an altogether smaller subshrub. The type-locality, if correctly recorded (as was not always the case) by Martius, should be somewhere on the west slope of Sa. do Espinhaço between Contendas and the S. Francisco river. When the pod is discovered the status of M. leptorachis in relation to M. somnians will require reassessment.