Monographs Details: Mimosa equisetum 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 equisetum Barneby
Synonyms:Mimosa heterophylla Hassl.
Description:Species Description - Small unarmed, wholly glabrous, loosely tufted herbs of idiosyncratic growth-form and foliage, the simple stems 1-3 dm either erect or incurved-ascending from a shortly branched subterranean caudex, bearing at crowded nodes up to or beyond middle delicate 1-jugate paucifo-liolate lvs and axillary peduncles, thence densely crowded subfiliform, at first red-orange but later greenish efoliate lf-stks forming a sterile grasslike terminal tuft, the solitary peduncles a little longer than or equalling the associated lf, the capitula globose. Stipules submembranous, those of lower lvs narrowly lance-subulate 1.5-2.5 mm, 1-nerved, persistent, those of distal lf-stks subsetiform shorter. Leaf-stalks of perfect lvs 1.5-2.5 cm x 0.2-0.3 mm, shallowly open-sulcate ventrally, espiculate; distal phyllodial lf-stks of same girth but 3-9 cm, shortly appendaged at apex and sometimes bearing 1-2 minute scales in place of pinnae; pinnae of perfect lvs 1-jug., the rachis 2.5-6 mm, the interfoliolar segments 0.5-1 mm; lfts 2-4-jug., the first pair 1-1.5 mm distant from the scarcely differentiated pulvinus, the paraphyllidia reduced to minute papillae or 0, or one of them resembling a minute lft; blade of lfts obovate or elliptic-oblanceolate 2.2-4.5 x 1-1.8 mm, at base obliquely cuneate or narrowly obtusangulate, at apex obtuse acuminulate, all veinless above, the subcentric midrib discolored dorsally but immersed. Peduncles 2.5-5 cm, strongly compressed; capitula without filaments 6-7 mm diam., prior to anthesis moriform; bracts linear-elliptic 1 mm long or less; flowers 4-5-merous diplostemonous, some lower ones staminate; calyx 0.4-0.5 mm, the deltate teeth 0.15-0.2 mm; corollas turbinate 3-3.5 mm, the membranous ovate, nearly plane lobes 1.1-1.4 x 0.8 mm, densely pallid-papillate around margin; filaments pink, monadelphous through ±0.5 mm, exserted 6-7.5 mm; ovary at anthesis glabrous; pod unknown.

Distribution and Ecology - In seasonally dry campo subject to periodic fire, ±400 m, known only from the Yhú—Monday watershed on the Paraguay Plateau shortly s. of 25°S, 56°W in depto. Caaguazú, Paraguay.— Fl. IX-X.

Discussion:

Hassler (l.c.) eloquently described his surprise at discovering this peculiar little mimosa flowering in early spring on campo burned the preceding fall. The perfect but greatly simplified lower leaves with axillary peduncles all crowded along the lower half or two thirds of the stem and concealed by a terminal plume of extremely fine grasslike phyllodia are unmatched in the genus. Hassler found the young phyllodia orange-red turning green in age, and likened them in mass to some species of horsetail (Equisetum). The only plausible relationship of M. equisetum seems to lie in the direction of M. paucifolia, M. piptoptera and M. phyllodinea, all endemic to planaltine Brazil, but it may nevertheless have arisen independently of these from a more generalized ancestor, perhaps akin to M. gracilis sensu lato.

Distribution:Paraguay South America| CaaguazĂș Paraguay South America|

Narratives:Mimosa equisetum