Mimosa guirocobensis

  • Title

    Mimosa guirocobensis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Mimosa guirocobensis Gentry

  • Description

    25. Mimosa guirocobensis  Gentry, Publ. Carnegie Inst. Wash. 527 (Rio Mayo pl.): 127. 1942.—"Type (5956) in Shreve Herbarium, Tucson, Arizona, collected near Guirocoba, southeastern Sonora, Mexico, April 6, 1940, by Howard Scott Gentry."—Holotypus not seen; isotypi, F! = F Neg. 54792, MICH! = MICH Neg. 5956, NY!; paratypus, Gentry 3020 from Jecopaco, F!

    Drought-deciduous few-branched shrubs 1-2 m flowering in spring from defoliate gray sticklike, strongly ribbed annotinous trunk or branches, randomly armed on some intemodes and on dorsal rib of some lf-stks with scattered erect aculei 1-2.5 mm, the stems, foliage and inflorescence densely silky-pilosulous throughout with fine loose, gray or yellowish hairs less than 1 mm, the dense cylindric fl-spikes borne on newly developing branchlets and subtended by coetaneous or hysteranthous lvs. Stipules erect, linear or linear-ligulate obtuse 3-15 x 0.4-1.2 mm, subinvolute, tardily deciduous. Lf-formula ii-iv/5- 7; lf-stks of developing lvs (mature summer foliage not seen) to 8-12 cm, the stout petiole 1.5-4 cm, the interpinnal segments mostly a little shorter, the ventral sulcus concealed by pubescence, spicules 0; rachis of longer pinnae 1-9 cm, the deflexed paraphyllidia 0.6-3 mm; lfts obliquely ovate or lance-ovate, either obtuse mucronulate or deltately subacute, the larger attaining 10-27 x 5—10(—16) mm, all 3-6-nerved from pulvinule, the slightly displaced midrib pinnately branched from below middle, the inner posterior nerve anastomosing near mid-blade, the anterior nerve (when present) and outer posterior ones much shorter, the venation sharply prominulous beneath, less so or subimpressed above. Peduncles 1-2 per node, stout, l-4(-6.5) cm; spikes without filaments 7-9 mm diam., the fls contiguous, the fl-buds obtuse, the filiform bracts 2-2.5 mm pilosulous, persistent; flowers 5-merous, normally 10-androus bisexual; calyx turbinate 1.7-2.7 mm, finely prominulously 5-nerved, pilosulous externally, the subulate unequal teeth 0.7-1.4 mm, on margin with a few thickened livid trichomes; corolla turbinate-campanulate 3-4.2 mm, the ovate 1-nerved lobes 1-1.4 x 0.8-11 mm, pilosulous externally and marginally fimbriolate with minute thickened processes; filaments free above immediate base, light purple, exserted 5-6 mm; ovary glabrous at anthesis, velutinous after fertilization. Pods scattered along spike-axis, in profile broad-linear, attenuate at base into the marcescent calyx, abruptly cuspidate, straight or almost so, overall 40-60 x 7.5-9.5 mm, the straight or shallowly undulate replum 0.6-0.8 mm wide, the stiffly papery valves colliculate over each seed, when ripe breaking up into 4-8 free-falling, individually dehiscent articles 5.5-10 mm long, the replum and valves alike densely softly velvety-pilosulous overall.

    On open grassy hillsides and slopes of barrancas at lower edge of the oak-belt, 550-1050 m, localized in the w. foothills of Sa. Madre Occidental in s.-e. Sonora, Mexico.—Fl. II-IV.

    This seldom collected mimosa seems related to M. guatemalensis and M. dysocarpa, and nearer the former in leaf-formula, but may be recognized by a peculiar growth-habit and rhythm of anthesis, by lack of interpinnal spicules, by thicker denser flower-spikes, and by relatively long calyx-teeth. The mature summer foliage has yet to be collected.