Monographs Details: Mimosa myuros 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.
Family:Mimosaceae
Scientific Name:Mimosa myuros Barneby
Synonyms:Mimosa cylindracea Benth., Mimosa verrucosa Benth.
Description:Species Description - Unarmed shrub or tree (stature not recorded) with amply microphyllidious foliage, pubescent with arborescently or, by shortening of the seta’s primary axis, substellately branched trichomes, the subconcolorous lfts either thinly strigulose or glabrate above, beneath thinly stellate overall or only on posterior half, the extremely slender flower-spikes usually 2-3 together in the axil of coevally expanding lvs. Stipules narrowly lanceolate 5-10 x 1-1.3 mm, firm, dorsally 1-nerved above middle, persistent. Leaf-stalks 6-11.5 cm, the petiole 20-40 x 0.6-1 mm, the interpinnal segments 6-15 mm; pinnae 5-9-jug., the larger ones at or beyond middle of lf-stk, their rachis 4-8 cm, the longer interfoliolar segments ±1.5 mm; lfts of longer pinnae (18-)25-37-jug., decrescent at both ends of rachis, the first pair 0.4-1.5 mm distant from subulate or minute conic paraphyllidia 0.3-1.5 mm, the blades oblong-ovate obtuse, the larger ones ±4-5.5 x 1.5-2 mm and 2.3-2.7 times as long as wide, all plane, veinless above, faintly 2-nerved beneath, the midrib a little forwardly displaced, the posterior nerve weak. Flower-spikes including short peduncle to 4 cm long and just prior to anthesis 3 mm diam.; bracts ovate, ±0.7 mm, thinly pilosulous dorsally; flowers 5-merous haplostemonous; calyx brownish, shallowly campanulate 0.5 mm, irregularly 5-6-toothed, the teeth low-deltate; corolla densely pallid-pubescent with entangled trichomes, ±1.3 mm, the ovate lobes ±0.6 mm; filaments (in bud) united basally into an obscure corona and alternating with minute blunt vestiges of staminodia; fruit unknown.

Distribution and Ecology - In unrecorded habitat but to be expected in moist montane woodland near 1600 m, collected twice, just prior to anthesis, high on Sa. da Mantiqueira near the s. border of Minas Gerais, Brazil: Fda. do rio Preto, near Itatiaia; Fda. S. Bento, near Passa Quatro, near 22°30'S, 45°W.—Fl. XII-?.

Discussion:

When I first encountered Glaziou 8651, mis-identified as M. verrucosa, I felt confident that the specimens represented an undescribed taxon of sect. Calothamnos, but the immaturity of the inflorescence precluded sure observation of the flower-structure. Toward the end of this study I came across confirmatory material in the National Herbarium at Rio de Janeiro, which, although again immature, has flowers on the verge of opening, sufficiently advanced to show that they are pentamerous, unlike those of other spicate Calothamnos, and haplostemonous, unlike those of M. verrucosa. Mimosa myuros, so named for the extremely narrow mouse-tail flower-spikes, is evidently a close relative of M. cylindracea. The leaf-formula is similar, except that both pinnae and leaflets attain slightly higher numbers, and the indumentum is similar, except less dense. The flower-spikes at comparable age and state of development are only 3 (not 4.5-5) mm in diameter. The extremely small size of the flower and its pentamerous perianth are, however, the decisive differential characters.

Distribution:Brazil South America| Minas Gerais Brazil South America|

Narratives:Mimosa myuros