Mimosa macrocephala Benth.
-
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
-
Type
420. Mimosa macrocephala Bentham, Trans. Linn. Soc. London 30: 398. 1875 & in Martius, Fl. bras. 15(2): 320, descr. ampliat. 1876. —"Habitat inter Goyaz et Cavalcante: Burchell n. 7518 et 7694."—Lectotypus, Burchell 7518, collected between Ribeirão dos Ma
-
Description
Species Description - Erect, amply leafy, functionally herbaceous unarmed subshrubs 3-7 dm from xylopodium, the few simple stems, lf-axes and peduncles hispid with erect tapering rufescent setae to 4.5-5.5 mm mixed with minute puberulence, the olivaceous foliage subconcolorous, the dorsally venose lfts puberulent or finely pilosulous on both faces and in addition thinly appressed-setose dorsally, ciliate with widely ascending setae not retrodecurrent into a continuous margin, the ellipsoid capitula solitary on stout ascending peduncle much longer than subtending petiole, often as long as or longer than the whole lf. Stipules erect firm reddish-brown lanceolate-acuminate 7-11 x 1.2-2.2 mm, coarsely 3-6-nerved, setose on back and margin, persistent. Leaf-stalks including discolored pulvinus 4-30(-35) mm, progressively shorter upward along stem, at middle 0.5-1.2 mm diam., the petiole almost or quite as long; pinnae of few early (often deciduous) lvs 1-jug. but of all middle and distal lvs 2-jug., the pulvini of the two pairs subcontiguous, the pinnae palmately spreading, recurved in sleep, the rachis of distal, usually longer pair (3-)4.5-8.5 cm, the interfoliolar segments 3-6.5 mm; lfts of distal pinnae (6-)10-16(-17)-jug., subdecrescent at each end of rachis or only proximally, the first, often unequal pair 1.3-3 mm distant from narrowly lance-attenuate paraphyllidia 1.3-3 mm, all in outline obliquely ovate- or lance-elliptic from broadly semicordate base, mucronulate-apiculate, those near mid-rachis 11-16 x 4-7 mm, 2-3.3 times as long as wide, all 5-6-nerved from pulvinule, the midrib displaced to divide blade ± 1:2-2.5,4-6-branched on each side from near middle upward, its posterior neighbor and the weaker submarginal anterior nerve brochidodrome well beyond mid-blade, the outer posterior ones much shorter. Peduncles widely or narrowly ascending 4-11 cm; capitula without filaments 8.5—10 mm diam., nearly twice as long, prior to anthesis conelike and hispid with bracteal setae; bracts linear-attenuate 2-4 x 0.25-0.5 mm, long-ciliate distally; flowers 4-merous 4-androus, some lower ones staminate or neuter and much smaller than the rest (no further described); calyx paleaceous spathiform 1.2-2.2 mm, asymmetrically developed on anterior side of fl, very short or obsolete on posterior side, the 1—2(—3) developed lobes irregularly setiform-decompound; bisexual corollas narrowly vaseshaped (2.8-)3-4.3 mm, the ovate apiculate navicular lobes 0.7-1 x 0.5-0.7 mm, weakly keeled and not thickened; filaments pink drying brown, monadelphous through 0.6-1.1 mm, exserted 3-4.5mm. Pods ±3-12 per capitulum, in profile linear-oblong, including stout terminal cusp 25-33 x 5.5-7(-7.5) mm, mostly 3-4-seeded, the undulately constricted replum 0.5-0.8 mm wide, densely hispid with stout pluriseriate, divaricate or ascending, tapering or flagelliform, stramineous sometimes brown-tipped setae to 5-7 mm, the firmly papery reddish-brown glabrous valves breaking up when ripe into free-falling biconvex articles 5-8 mm long; seeds plumply lenticular, in broad view ±5x4 mm, the testa dull reddish- brown, smooth.
Distribution and Ecology - On sandy or rocky soils in cerrado at ±700-800 m, apparently local on both slopes of the Maranhão-Corumbá watershed between 14°30' and 16°S in centr. Goiás.—Fl. XII-II.
-
Discussion
Bentham considered M. macrocephala distinct from other members of his ser. Hirsutae because of its ellipsoid rather than subspherical capitula, but it is now known that other so-called Hirsutae, including the very closely related M. procurrens, may have flower-heads longer than wide. Mimosa procurrens and M. macrocephala are alike in indumentum, foliage, corolla and craspedium, the most immediately striking difference being in habit of growth, the former having pliantly humifuse stems whereas the latter is erect. Closer scrutiny reveals that the calyx of M. macrocephala is better developed on the flower’s posterior side, where it is plainly paleaceous, whereas the equivalent lobe in M. procurrens may be reduced to a few random setae. Both species are known to occur in Goiás on upper forks of rio Corumbá in the foothills of Sa. dos Pirineus, but M. macrocephala extends northward from there to the sources of rio Maranhão and M. procurrens eastward into Distrito Federal. They are not known to occur in direct association where their ranges overlap and they appear to be sibling species, doubtless differentiated from a common progenitor but now effectively vicariant in dispersal. Fieldwork is required to determine whether the separation is as abrupt as it now appears.
-
Distribution
Maranhão Brazil South America| Goiás Brazil South America|