Mimosa rocae Lorentz & Niederl.
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Authors
Rupert C. Barneby
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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.
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Family
Mimosaceae
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Scientific Name
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Type
215. Mimosa rocae Lorentz & Niederlein, Informe cient. Exped. Rio Negro, Bot. 213, lam. 3. 1881.-“[Argentina. Buenos Aires:] . . . en la Sierra Currumalan-30,IV. Sierra de la Ventana-l.V.”-Holotypus (Burkart, 1948: 127), Lorentz 13, +B = F Neg. 1433!; iso
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Description
Species Description - Prostrate unarmed microphyllous shrublet from stout woody base forming intricately branched mats of foliage 4-14 dm diam., the defoliate trunks brown glabrate, the young stems, foliage and fls sordidly gray-stellate-lepidote with multiradiate, almost stemless setulae, the small crowded lfts paler and a little more densely pubescent above than beneath, the globose capitula solitary and paired in distal lf-axils on peduncle longer than subtending lf. Stipules firm erect subulate 0.4-1.4 mm, tardily deciduous. Petioles including hard pulvinus 0.7-3(-4) mm, at middle 0.3-0.4 mm diam.; pinnae 1-jug., the rachis 4-12mm, the interfoliolar segments 0.4-1 mm; lfts of longer pinnae (5-)7-12-jug., scarcely graduated, the blades linear-oblong to narrowly elliptic from obliquely truncate base, obtuse at apex, the longer ones 1.5-4 x 0.6-1.5 mm, 2-3.5 times as long as wide, all veinless above, the simple subcentric midrib bluntly prominulous beneath. Peduncles (5-)6-27 mm; capitula without filaments 5-6 mm diam., prior to anthesis moriform, the obtuse fl-buds densely stellate, the receptacle ±1.5 mm; bracts triangular-ovate to oblanceolate 0.4-0.7 mm, persistent; flowers 4-merous 4-androus, all bisexual; calyx shallowly campanulate 0.4-0.5 mm, glabrous externally, the subundulate rim minutely ciliolate; corolla turbinate-campanulate 2.4-2.9 mm, the rather thick-textured yellowish deltate-ovate lobes 1-1.4 x 0.8-1 mm; filaments yellow, united at very base to the corolla but free from each other, exserted 1.5-2 mm; staminodia 0; ovary densely stellate after fertilization. Pods ascending, 2-10 per capitulum, sessile but cuneately attenuate at base, in profile undulately linear, nearly straight, (7-) 1020 x 3.5-4 mm, (l-)2-4-seeded, the shallowly constricted replum 0.4-0.5 mm wide, the papery valves low-convex over each seed, the replum and valves alike densely sordid-tomentulose with strictly stellate or depressed-arborescent setulae to 0.15 mm tall, the ripe valves breaking up into free-falling, individually dehiscent elliptic articles ±5-6 mm long; seeds dark brown ±4x3 mm.
Distribution and Ecology - In thin stony soil and on exposed arenitic rock, locally plentiful near 200-700 m on the sierras pampeanas of s. prov. Buenos Aires (Sa. Bravard and de la Ventana; Sa. de Tandil) and s. Uruguay (deptos. Lavalleja and Maldonado); doubtfully reported from s. end of Sa. do Mar in Rio Grande do Sul (Burkart, 1964: 397), but this is not confirmed by Lins (1984: 53).—Fl. IX-XII.—Zarza; zarzaparilla.
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Discussion
A matted shrublet, related to M. pilulifera but notably different in habit, habitat, and dense stellate indumentum, M. rocae is, with M. tandilensis, the species of Mimosa extending furthest south in South America, to latitude 38°30'S.
Mimosa rocae was collected for the first time by Friedrich Sellow, perhaps in Uruguay, but no exact locality is on record. Sellow’s material in the Hooker herbarium at Kew was annotated by Bentham as M. incana.
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Distribution
Uruguay South America| Argentina South America| Buenos Aires Argentina South America| Brazil South America| Rio Grande do Sul Brazil South America|