Monographs Details: Mimosa piresii 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 piresii Barneby
Synonyms:Mimosa macropogon Barneby
Description:Species Description - Stout, amply leafy macrophyllidious, erect or sometimes subsarmentose shrubs or subshrubs attaining 12 dm or more, with few large lvs below or mostly below mid-stem, strigose-pilose throughout with forwardly incurved or subappressed tapering, minutely scaberulous setae ±0.5-1.5 mm, the foliage bicolored, the dried lfts dark brown sublustrous but setulose above, beneath paler brown and, especially along primary nerves, more densely pubescent, the paniculate-thyrsiform efoliate inflorescence rising up to 9 dm above foliage. Stipules firm, lance-ovate 3-6 x 2-3 mm, densely setose dorsally, glabrous within, persistent. Leaf-stalks 9-18 cm, the petiole 3-6 cm, at middle 2-3 mm diam., subterete, the interpinnal segments 1.5-3.3 mm; pinnae 4-7-jug., a little accrescent distally, their often backwardly arched rachis (5-)6-10 cm, the interfoliolar segments mostly 10-18 mm; lfts 5-9-jug., little or markedly accrescent distally, the subequilong first pair 3-6 mm distant from subulate paraphyllidia 1-1.5 mm, the blades obliquely oblong-elliptic, ovate or obovate, obtuse but minutely apiculate, (17-)20-35 x 10-25 mm, 1.4-2 times as long as wide, at base deeply cordate on proximal side and shallowly so or merely rounded on distal one, the plane margin strigulose like the faces, the dorsal face palmately (3-)4—5-nerved from short pulvinule, the stout straight midrib displaced to divide blade ± 1:1.5-2, pinnately 4-6-branched from below middle, the inner posterior nerve produced beyond mid-blade, the outer primary nerves short and weak. Peduncles solitary and 2-3 per node, (0.7-) 1-2.5 cm, 1-3-bracteolate above middle or immediately below the globose capitulum, this prior to anthesis conelike, the ellipsoid receptacle becoming 2-3 x 1.5-2 mm; bracts linear-oblanceolate or spatulate 2-3 x 0.3-0.4 mm, densely silky-setulose distally, about as long as the densely silky fl-buds; flowers 4-merous 8-androus, mostly bisexual; calyx paleaceous-pappiform 1.5-2.7 mm, the externally glabrous or setulose tube 0.3-0.5 mm, the lobes decompound nearly to base into stiff whitish setae to ± 1.1-1.5 mm; corolla narrowly turbinate 3-3.8 mm, the tube glabrous externally, the ovate involute 1-nerved lobes 1.2-1.6 x 0.8-1 mm, densely setulose externally; filaments pink or seemingly whitish, monadelphous through 0.5-1.3 mm below the ovary, exserted ± 3.5-5.5 mm. Pods to nine per capitulum, subsessile, when well fertilized undulately linear in profile 25-42 x 5-6 mm, 5-8-seeded, the shallowly constricted replum 0.6-1 mm wide, the stiffly papery valves low-convex over each seed, the replum and valves alike strigose overall with subappressed scaberulous setae to ± 1 mm long and to ±0.2 mm diam. at dilated base, these mixed with a few short capillary trichomes, the ripe valves breaking up into free-falling, individually indehiscent articles 5-7 mm long; seeds compressed-obovoid ±4x3 mm, the testa dull brown.

Distribution and Ecology - In open stony campo, sometimes near rock outcrops, ±300 mm, local between 6°-9°35'S and 48°-55°W in s. Pará and immediately adj. Mato Grosso (middle Xingú valley s.-w. to Sa. do Cachimbo) and far n. Goiás (Cachoeira dos Mar- tirios on rio Araguaia) in Amazonian Brazil.— Fl. (?-)III-VII(-?).

Discussion:

Ample leaves that resemble, except for setose indumentum and lack of nectary, those of M. (Mimadenia) pithecolobioides are combined in M. piresii with an effusely branching panicle of small globose capitula, a pappiform calyx, and basally monadelphous filaments. In collections from southern Pará and Mato Grosso the calyx tube is glabrous externally and the filaments appear to have been white, whereas in those from northern Goiás the calyx is silky-setose externally and the petals are reported pink.

Distribution:Brazil South America| Mato Grosso Brazil South America| Goiás Brazil South America| Pará Brazil South America|

Narratives:Mimosa piresii