Mimosa acroconica 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 acroconica Barneby

  • Type

    223bis. Mimosa acroconica Barneby, sp. nov., habitu indumentoque cum M. caliciadenia arete congruens, sed foliis sessilibus (primum pinnarum par juxta folii pulvinum ipsum oritur) et stipulis magnis chartaceis, ad inflorescentiae junioris apicem imbricati

  • Synonyms

    Mimosa caliciadenia Barneby

  • Description

    Species Description - Openly branched, prickly and viscid, arborescent shrubs with incurved-ascending branches, attaining 4 m, armed on flowering stems and on back of lf-stks with few scattered, horizontal or widely acroscopic, yellowish aculei ±1-2 mm, the stems in addition densely finely villous with erect shining hairs less than 0.5 mm and hispid with many erect, gland-tipped setae 0.5-1.5 mm and a few scattered, tapering eglandular ones, the foliage olivaceous subconcolorous, the lfts facially glabrous or almost so, minutely ciliolate, the relatively loose capitula solitary and paired in the axils of a succession of coevally expanding lvs, when very young subtended and concealed by a cone of ample papery stipular bracts, the inflorescence paniculate, openly foliate. Stipules caducous from a wide lunate scar, all fallen from developed lvs and from base of peduncles at anthesis, those subtending nascent capitula papery-membranous, ovate-acuminate, dorsally gibbous, 6.5-12 x 4-8 mm, the blade silky-pilosulous but eglandular dorsally, glabrous and finely several-nerved within. Leaves sessile, the short first pair of pinnae directly next to discolored pulvinus, the rachis of lvs below the inflorescence 5-16 cm (upper lvs shorter and simpler, no further described), the longer interpinnal segments 8—12(—15) mm, the ventral sulcus narrow, bridged and minutely spiculate between pinna-pairs; pinnae 5-14-jug., accrescent distally, the rachis of distal pair 2.5-3.5 cm, the longer interfoliolar segments 1-1.5 mm; lfts of distal pinnae ± 17-24(-28)-jug., little graduated, the first pair close beyond minute subulate paraphyllidia, the blades narrowly oblong from shallowly semicordate base, broadly rounded at apex, the largest 5-7.5 x 1.7-2 mm, all almost veinless above, beneath 3—4-nerved from pulvinule, the midrib subcentric, finely 1-2-branched well above midblade, the inner posterior nerve produced nearly to blade apex, the margin plane. Peduncles 2.5-4 cm; capitula plumply ellipsoid or ovoid, prior to anthesis conelike, without filaments to 12 x 9 mm diam., the slenderly clavate receptacle to 7.5 x 1.2 mm; bracts elliptic-oblanceolate 3-5 x 1-1.5 mm, surpassing but scarcely concealing the obovoid obtuse, subglabrous fl-buds, early deciduous, the claw glabrous, the thin-textured blade brownish, dorsally pilosulous; flowers 4-merous 8-androus, many lower ones staminate; calyx shallowly campanulate ±0.5 mm, the membranous tube externally glabrous, the low-deltate lobes randomly minutely setulose-ciliolate; corolla broadly turbinate but contracted at base into a neck nearly 0.5 mm, that of longer flowers 3.5-4.1 mm, the broadly deltate-ovate, pink, 1-nerved lobes ±1-1.2 x 1-1.2 mm; filaments bright pink, monadelphous through ±0.7 mm, exserted 10-11.5 mm; ovary setulose; ovules ±6; pod not known.

    Distribution and Ecology - In campo rupestre at ±1000 m, known only from Sa. do Cabral, near 17°40'S in centr. Minas Gerais, Brazil.—Fl. II—III(—?).

  • Discussion

    Mimosa acroconica is clearly related to M. caliciadenia, of which it has the armament of scattered aculei and the pin-shaped setae concave and resiniferous at tip, but differs in two striking particulars: truly sessile leaves; and extraordinary dilated stipules, the papery sheath of which falls precociously from a lunate scar. The similar bractlike stipules that subtend nascent capitula are imbricate at the tip of inflorescence branchlets into a loose cone of scales much like that seen in some species of Desmodium, but unexpected in Mimosa. It is to this feature that the epithet alludes.

    I am much indebted to Dr. J. R. Pirani for the loan and gift of the type material.

  • Distribution

    Brazil South America| Minas Gerais Brazil South America|