Monographs Details: Mimosa humivagans Barneby
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.
Synonyms:Mimosa prorepens Barneby
Description:Species Description - Functionally herbaceous unarmed subshrubs from xylopodium, the pliantly humifuse, distally few-branched stems attaining ±15 dm, together with lf-and inflorescence-axes at once densely puberulent with small incurved pallid hairs and hispid with erect tapering tawny setae to 1.5-3 mm, nowhere glandular, the subconcolorous brownish-olivaceous lfts glabrous on both faces, minutely ciliolate, the lax pseudoracemes of small globose capitula efoliate or almost so, terminal to main stem and branches, exserted 1.5-3 dm from developed foliage. Stipules widely ascending or deflexed, lanceolate 3-5 x 0.7-1.1 mm, the firm blades indistinctly 5-7-nerved, puberulent on both faces, setose-ciliate, persistent. Leaves subsessile, the whole lf-stk 2.5-5.5 cm, the petiole proper and pulvinus together only 2-3.5 mm, the longer interpinnal segments 3.5-6 mm, the ventral groove bridged between pinna- pairs but spicules 0; pinnae of larger lvs 7-12- jug., a little decrescent at each end of lf-stk, the axis of longer ones 13-21 mm, the interfoliolar segments to 0.8-1.2 mm; lfts of longer pinnae 10-15-jug., little graduated, the small first pair 0.2-0.6 mm distant from pulvinus (paraphyllidia 0), the blades narrowly oblong obtuse from proximally obtusangulate base, those at mid-rachis ±3-5 x 0.8-1.3 mm and ±4 times as long as wide, all veinless above, the subcentric midrib and one short posterior nerve weakly prominulous beneath. Peduncles mostly solitary, a few geminate, 20-27 mm; capitula without filaments 6-7 mm diam., prior to anthesis moriform; bracts linear-oblanceolate to ±1.5 mm, beyond middle pectinately setose-ciliate, the cilia basally confluent; flowers 4-merous, 8-androus, some lower ones staminate; calyx shallowly campanulate or bowl-shaped 0.3 mm deep, the tube glabrous externally, the rim with a few setulae ±0.2 mm; corolla to 4 mm, subcylindric, the ovate subacute, shallowly concave 1-nerved lobes 0.9 x 0.6 mm, appressed-setulose externally; filaments lavender-pink, monadelphous through nearly 1 mm, the 4 longer ones exserted ±7.5 mm; ovary following fertilization densely coarsely setose; the full-grown pod unknown.
Mimosa humivagans and sibling M. prorepens have been collected close together, but in spite of resemblances in habit and vesture I cannot construe them as other than distinct species, so different are the numbers of pinnae and the proportions of calyx to corolla, as described in the foregoing diagnosis. The ripe pod of neither is yet known, so that their affinities within sect. Pachycarpae remain open to revision. In many respects they resemble aspects of the polymorphic M. foliolosa, but differ collectively in pliantly humifuse stems arising anew each year from a woody rootstock. In this growth-habit and further in subsessile leaves M. humivagans recalls M. (Paucifoliatae) pratincola, but differs from it (inter alia) by hispidly setose (not simply puberulent) stems and leaf-stalks, absence of paraphyllidia, leaf-formula attaining vii-xii/10-15 (not v-viii/7-10), and pubescent corolla-lobes and ovary.