Mimosa acutistipula

Title

Mimosa acutistipula

Author(s)

Rupert C. Barneby

Scientific Name

Mimosa acutistipula (Mart.) Benth.

Description

63. Mimosa acutistipula (Martius) Bentham, J. Bot. (Hooker) 4: 391. 1842, based on Acacia acutistipula Martius, Flora 20(Beibl. 2): 107. 1837.—Typus sub var. acutistipula indicatur.

Tall shrubs and treelets attaining 4-5 m, commonly armed on intemodes with tough broad-based blackish, either erect or forwardly curved aculei 1.5-5 mm, but some leafy branchlets (perhaps some whole trees) unarmed, the homotinous growth pilosulous throughout or almost so with fine erect plain hairs 0.1-0.3 mm mixed with minute livid granules, the olivaceous lfts concolorous or slightly paler beneath, often brunnescent in drying, the firm plane lfts either puberulent on both faces or glabrous ciliolate, the inflorescence a pseudoraceme or narrow few-branched panicle of fl-spikes either fully exserted from foliage or leafy-bracteate proximally. Stipules erect firm, subulate or linear-lanceolate 2-7 x 0.7-0.9 mm, puberulent within and without, bluntly 1-nerved dorsally, tardily deciduous. Leaf-stalks 3.5-10 cm, the petiole including oblong-ellipsoid livid pulvinus 7-16 x 0.5-0.9 mm, the longer interpinnal segments 7-13 mm, the ventral sulcus interrupted between pinnae by a bridge sometimes produced into an inconspicuous puberulent spicule; pinnae of major lvs 4- 10(-1 l)-jug., the lowest a little shorter than the rest, the rachis of distal ones (2.5-)3-5.5 cm, the longer interfoliolar segments 1.3-2 mm; lfts of longer pinnae 20-3 l(-33)-jug., the first pair 0.7-1.5 mm distant from subulate paraphyllidia erect or deflexed from pinna-axis, the blades in outline narrowly oblong or broadly linear, abruptly acute, the longer ones usually ±5-7 x 1.2-1.6 mm, in s. Bahia to 10(—12.5) x 2.5 mm, all veinless above, the moderately displaced midrib and 1 (-2) posterior nerves from pulvinule slenderly prominulous dorsally, the midrib giving rise on each side near and beyond mid-blade to (l-)2 (-3) secondary venules. Flower-spikes 1—3(—4) per node of inflorescence, the axis including short peduncle 2-7.5(-8) cm; bracts narrowly elliptic or oblanceolate 0.6-1 mm, caducous; fl-buds plumply obovoid, not angulate, usually glabrous, sometimes microscopically papillate or puberulent at apex; flowers 4-merous 8-androus, many or almost all in some spikes staminate; calyx membranous campanulate 0.5-0.7 mm, the low-deltate teeth ±0.1 mm, the rim minutely ciliolate, often with a few gland-tipped trichomes; corolla turbinate-campanulate or obovoid-turbinate 1.8-2.1 mm, whitish pink-tinged or in age bright pink, the ovate plane or slightly concave 1-nerved lobes 0.8-1.1 x 0.7-0.85 mm; filaments white or cream-colored, free, the longer ones exserted 3.2-4.3 mm; ovary short-stipitate, glabrous or microscopically glandular-puberulent. Pod stipitate, the stipe 5-9 mm, the broad-linear planocompressed body (45-)50-70(-75) x 7-9.5 mm, cuneately tapering at base, obtuse at apex, when well fertilized 6-9(-10)-seeded, the straight or very shallowly undulate replum 0.4-0.7 mm wide, the papery lustrous purplish-red but brunnescent or finally blackish, glabrous or microscopically puberulent valves delicately reticulate-venulose and granular, breaking up into free-falling, inertly dehiscent articles 5-7 mm long; seeds discoid ±5-5.8 x 4-5 mm, the brown testa smooth but not highly lustrous.

Due to a general similarity in foliage and in white flower-spikes M. acutistipula and M. arenosa have often been confused in herbaria, but may be distinguished at anthesis by shape of the flower and in fruit by presence or absence of stipe; for details see key to ser. Leiocarpae. The more tenuous differences between M. acutistipula and M. dichroa, of which the pod is as yet unknown, are mentioned under the latter. While the individual flower and pod of M. acutistipula remain virtually constant in size and form over the whole range of the species, there is a marked difference between groups of more southern and more northern dispersal in leaf-formula and in length and density of the flower-spikes. I therefore propose to distinguish two varieties.