Monographs Details: Mimosa
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1991. Sensitivae Censitae. A description of the genus Mimosa Linnaeus (Mimosaceae) in the New World. Mem. New York Bot. Gard. 65: 1-835.
Family:Mimosaceae
Scientific Name:Mimosa
Description:Species Description - Stiffly branched microphyllous shrub with fuscous lenticellate, wide-angled flexuous branches, armed at nodes with a pair of broad-based infrastipular aculei to 3-4 mm, the lf-axes and brachyblasts minutely whitish-puberulent, the small subglobose capitula arising with lvs from brachyblasts along annotinous branches. Stipules subulate 1-2 mm, those of primary lvs deciduous, those of brachyblasts internally villosulous. Leaf-formula (so far as known from flowering specimen) ii-iv/6-9, the lf-stk of fasciculate lvs 3-18 mm, the petiole 1.5-8 mm, the longer interpinnal segments 1.5-4 mm, the lfts narrowly oblong ±1.5-2.5 x 0.4-0.7 mm, faintly 1-nerved dorsally [primary lvs of long-shoots could be more elaborate and larger]. Peduncles 1-2 per brachyblast 5-8 mm; capitula without filaments 4-4.5 mm diam., moriform, the obovoid-pyriform fl-buds glabrous; flowers 5-merous 10-androus, glabrous, "pinkish"; calyx 0.7-1.9 mm, a little less than half as long as corolla, this 2-2.3 mm, its lobes 0.6-1 mm; filaments almost free, exserted 3-3.5 mm; pod unknown.

Discussion:

The plant described above was distributed as M. grahamii, but appears more closely related to M. aculeaticarpa var. biuncifera, of which it may even be an extreme xeromorphic form. Normally, the capitula of M. aculeaticarpa are borne exclusively on coevally expanding long-shoots, whereas here all are produced from hemispherical brachyblasts on annotinous branchlets. Furthermore the calyx is shorter than normal in even the smallest, most xeromorphic expressions of var. biuncifera. Cajeme (now Ciudad Obregón) is situated on the floor of the Sonoran Desert in the lower Yaqui valley, in the Foothills of Sonora zone as defined by Shreve & Wiggins (1964, vol. 1, map 1); typical var. biuncifera is a typical element of grassland at levels well above the Sonoran Desert. The fruit is required for taxonomic evaluation.