Mimosa papposa

  • Title

    Mimosa papposa

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Mimosa papposa Benth.

  • Description

    397. Mimosa papposa Bentham, J. Bot. (Hooker) 4: 375. 1841.—Typus infra sub var. papposa indicatur.

    Stiffly erect subshrubs ±7-10 dm, closely resembling M. pyrenea and M. venatorum in habit, inflorescence and individual fl, the former especially in subsessile lvs and glaucous stramineous-marginate lfts, but different from both in shorter lf-stks and fewer lfts per pinna, the pseudoracemes of capitula rising 1.5-2.5 dm above developed lvs. Stipules (few seen) linear-lanceolate 5-6 mm, caducous. Leaf-stalks including pulvinus less than 3 mm; rachis of longer pinnae 4-7 cm, the longer interfoliolar segments 1-2 mm; lfts of longer pinnae (25-)28—45-jug., linear-oblong or lance-ovate, acute or apiculate, straight or a little arched forward, those near mid-rachis 5-10.5 x 1-2.5 mm, 2.4-5.5 times as long as wide, all smooth above, beneath faintly 3-6- nerved from pulvinule but the nerves only weakly prominulous, the midrib, when perceptible, dividing blade ±1:2. Peduncles solitary (2-)4-35 mm; capitula globose, without filaments 7.5-9 mm diam., prior to anthesis moriform, the fl-buds minutely papillose-puberulent; bracts linear-spatulate 1.3-2 x 0.3 mm, thinly setulose at tip; flowers with paleaceous 1.6-2.4 mm calyces, the deeply decompound lobes subpappiform; corolla 2.8-3.6 mm, the cymbiform lobes 1.1-1.5 x 0.5-0.6 mm; filaments pink, monadelphous through ±1.5 mm, exserted 5.5-6.5 mm. Pods (few seen) few per capitulum, in profile undulately oblong, to 4-seeded and ±30x7 mm, the replum 0.5-0.6 mm wide, the planocompressed, free-falling indehiscent articles 7-8 mm long, like the replum densely pilose with forwardly subappressed, tapering yellowish, microscopically scaberulous setae to 1-2.5 mm.

    Mimosa papposa, M. pyrenea and M. venatorum constitute a replacement-series of which the collective range is nearly repeated in sect. Habbasia ser. Pachycarpae by M. setosissima, and M. densa, each group having a member endemic to or represented on Chapada dos Veadeiros, Sa. dos Pireneus, and Sa. dos Cristais, islands of arenitic caprock rising from an ocean of cerrado. Each group consists presumably of relic expressions of a homogeneous, widespread type, their insular nature having encouraged genetic drift and the fixation of a new specific identity. Mimosa papposa differs from its two closest relatives, M. pyrenea and M. venatorum, in fewer leaflets (in larger leaves less, not more than fifty pairs); further from M. pyrenea in longer, less crowded leaflets, and in completely leafless pseudoracemes; and further from M. venatorum in abbreviated leaf-stalk in all leaves, pinnae only half as long, and glaucescent leaflets almost nerveless dorsally. The less closely related M. hypoglauca, allopatric to the north and east, differs in mostly foliate pseudoracemes and leaflets essentially 2-, not 3-6-nerved from pulvinule. So far as known today M. papposa is of sparing occurrence on the headwaters of rio Maranhão in the northwestern comer of the Federal District and in adjoining Goiás, and is represented on Sa. dos Cristais by a weakly differentiated variety, these separable as follows: