Mimosa grahamii

  • Title

    Mimosa grahamii

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Mimosa grahamii A.Gray

  • Description

    40. Mimosa grahamii  A. Gray, Pl. wright. 2: 52. 1853.—Typus infra sub var. grahamii indicatur.

    Shrubs 6-20 dm, armed at most nodes with a pair of straight, widely ascending hornlike infrastipular aculei 3-10 mm and randomly on intemodes with a solitary recurved infrapetiolar one, the young stems, foliage, and usually the aculeate lf-axes pilosulous with soft erect-ascending hairs 0.2-0.4 mm, exceptionally subglabrous, the pale green concolorous lfts either facially glabrous ciliolate or pilosulous on both faces, the globose capitula axillary to coeval lvs on homotinous branchlets. Stipules papery brownish 2-6(-12) mm, usually ligulate obtuse, incurved and 2-3-nerved distally, or some lower ones ovate, rarely the longer ones attenuate subsetiform. Leaf-formula v-ix(-xii)/(7-)9-l 7(-20), the lf-stks (3—)3.5—11 cm, the ventral sulcus continuous (spicules 0), the pinna-pairs seldom exactly opposite; rachis of longer pinnae 12-33 mm; lfts lance- or ovate-oblong, obtuse or acute apiculate, the larger ones (2.5-)3-6(-6.5) x 1-2.1 mm, 2.2-3.5(-3.8) times as long as wide, all vein-less ventrally, dorsally 2-3-nerved from pulvinule, the moderately displaced midrib pinnately 2-3-branched on each side, the inner posterior
    nerve brochidodrome beyond mid-blade, the venulation becoming prominulous and pallid in age. Peduncles solitary and 2-3-nate, (1-) 1.5-3.5 cm; capitula without filaments (6-)7-9.5 mm diam., moriform, the fl-buds either glabrous or pilosulous, the clavate receptacle 1.5-4 mm long; flowers 5-merous 10-androus, sessile or almost so, all bisexual; calyx narrowly campanulate (1.2-) 1.5-2.2 mm, the minute teeth 0.1-0.2 mm, sometimes tipped with a reddish granule, the orifice otherwise either glabrous or ciliolate; corolla subtubular (3-)3.3-4.8 mm, the almost erect lobes 0.8-1.2 mm, either glabrous or thinly pilosulous externally; filaments whitish, sometimes fading cream-color, united at very base to corolla, exserted 4-6 mm. Pods 1-7 per capitulum sessile or contracted at base into a stipe to 2 mm, in profile narrowly oblong to linear, straight or gently decurved, (15-)20-57 x 4.5-7 mm, 3-8-seeded, the stout, straight or shallowly undulate replum randomly armed with few distant erect aculei     0.5-2.5 mm, the stiffly papery, dark brown, vestigially puberulent but often densely granular valves low-umbonate over seeds, when ripe falling from replum in one piece.

    In the context of its group M. grahamii is distinguished by relatively ample leaves and by prominulous dorsal venulation of the leaflets. In the typical variety the pod is relatively short and broad, with replum not or scarcely constricted, and provides space for the seeds to lie obliquely across the cavity. In the habitally identical M. prolifica, which is here considered only varietally distinct, the longer narrower, undulately constricted pod confines the seeds to an essentially vertical orientation. The pubescence of foliage and flowers varies notably between populations of M. grahamii, but the less common glabrate form occurs entirely within the range of its pubescent counterpart, and intermediates between the extremes (noted as numerous by Kearney & Peebles, Arizona Flora 401. 1970, but denied by Isely, 1971b: 418) make precise definitions difficult.