Mimosa pycnocoma

  • Title

    Mimosa pycnocoma

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Mimosa pycnocoma Benth.

  • Description

    253. Mimosa pycnocoma Bentham, J. Bot. (Hooker) 4: 405. 1842.—"Brazil, Pohl."— Holotypus, Pohl d.1408 = 1927, collected  VII.1819 (fl) "ad Serra do S. Felix prope Rio Trahiras [centr. Goiás near 13°30'S]", K!; isotypi, GH! NY! US! W!; probable isotypus, Pohl s.n., M!—Wrongly equated by Bentham, 1875: 440, 1876: 389, with M. claussenii.

    Probably arborescent but stature not recorded, the epidermis of defoliate annotinous branches early exfoliating and exposing cinnamon-brown wood, the homotinous branch-tips densely leafy unarmed, setose with ascending, basally bulbous but distally fine silky flagelliform setae to ±6 mm, the lf-stks setose with similar but retrorsely descending setae, the smooth, when dry dark brown lustrous leaflets facially glabrous ciliate, the inflorescence (known only in early anthesis) a small subcorymbose pseudoraceme of subglobose capitula nestling in foliage. Stipules broadly triangular-ovate-acuminate ±7-8 x 4 mm, the firm blade densely pilose dorsally, glabrous castaneous within, deciduous. Leaf-stalks 9-13 cm, the petiole and obese pulvinus together 1-1.5 cm, the longer interpinnal segments ±6-7 mm, the ventral groove bridged between pinna-pairs but spicules 0; pinnae 12-17-jug., strongly decrescent proximally, scarcely so distally, the rachis of longer ones 4-5 cm, its longer interfoliolar segments ±1.5 mm; lfts of longer pinnae ±25- jug., the first pair next to pulvinus (paraphyllidia 0), all in outline narrowly oblong obtuse mucronulate, the longer ones attaining 7x1.5 mm, the blades ciliate when young with fine pliant setae, these distally eroded in age. Peduncles ±3.5 cm; capitula without filaments ± 10 mm diam., prior to anthesis densely silky-setose overall; bracts oblanceolate ± 3 mm, dorsally setose from base upward, the longer distal setae as long as the bract itself and surpassing the associated fl; flowers 4-merous 8-androus, the lowest staminate; calyx ±0.3 mm, glabrous externally, the rim densely setose with plain cilia to ±1.7 mm; corolla 3.5-4 mm, the narrowly funnelform tube glabrous, the ovate incurved lobes ± 1 mm, silky-setulose dorsally; filaments (probably pink) monadelphous through 0.7-1.2 mm, exserted ± 8 mm; pod unknown.

    Habitat not recorded, but to be sought in campo rupestre at or above 1000 m, known only from the type collection from the Tocantins-Paranã divide near 13°30'S in centr. Goiás, Brazil.—Fl. VII-VIII(-?).

    Mimosa pycnocoma, described by Bentham in his first paper on Brazilian Mimosa, was referred without comment in his summary monographs (1875, 1876) to the synonymy of M. claussenii. Its close relationship lies, I believe, in the direction not of M. claussenii but of the arborescent group clustering around M. setosissima of Sa. dos Pireneus, M. decorticans of Sa. dos Cristais, and M. densa and M. laniceps of Chapada dos Veadeiros, with all of which it shares the striking feature of exfoliating epidermis of year-old stems and, inferentially, a framework of cinnamon- brown branches. It differs from M. setosissima in the longer finer setae of stems and young leaflet-margins, in absence of glandular setulae, in larger and fewer leaflets, in smaller capitula composed of flowers shorter by one-third, and in much shorter, densely ciliate calyx. Mimosa densa and M. laniceps differ collectively from M. pycnocoma in abbreviated pinnae attaining at most 16-30 (not 40-50) mm in length, and M. laniceps, which is geographically the nearer, further in silky-tomentose vesture and substantially longer flowers.