Monographs Details: Mimosa rhodostegia 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
Synonyms:Mimosa regina Barneby
Description:Species Description - Arborescent shrubs attaining 4 m, the trunk-diam. unknown, the unarmed, densely amply leafy branchlets to ±4 mm diam., except for glabrous upper face of very numerous small lfts softly viscid-villosulous throughout with fine white eglandular hairs intermixed with slender gland-tipped setulae, the lf-axes in addition hispid with fine yellowish setae to 2-6 mm, the inflorescence in early anthesis a congested terminal pseudoraceme ±1.5 dm of subglobose capitula subtended by dilated papery stipules and emergent juvenile lvs, the fruits (known only from annotinous examples) probably immersed in foliage. Stipules ovate-acuminate 15-25 x 7-13 mm, united behind petiole through 1/3-½ their length, the early deflexed persistent blades papery reddish-brown, striately many-nerved, villosulous on both faces, the exterior margin often obscurely denticulate. Leaf-stalks 10-22 cm, the petiole ±5 x 1.5 mm, the longer interpinnal segments 4-6 mm; spicules 0; pinnae 25—44-jug., decrescent proximally but otherwise subequilong, the rachis of longer pinnae 22-32 mm, the first pair of lfts close to pulvinus (paraphyllidia 0), the longer interfoliolar segments 0.5-0.8 mm; lfts of longer pinnae 30-45-jug., very densely obliquely imbricate, in outline linear-oblong obtuse straight, the larger ones 3-4 x 0.6-0.8 mm, all 3-nerved from pulvinule, the centric midrib 1-2-branched beyond middle. Peduncles slender 2.5—4 cm; capitula without filaments ±12 mm diam., prior to anthesis comose with emergent bracts, these narrowly lanceolate, attenuate from middle toward each end, (4-)5-7 x 0.6-0.8 mm, the firm blade thinly villosulous and glandular-setulose dorsally, pectinately setose-ciliate; flowers 4-merous 8-androus, the lower ones staminate and a little shorter than the bisexual ones; calyx campanulate 0.6-1 mm, externally glabrous, the rim with unequal cilia to 0.4-0.7 mm; corolla 4.5-6 mm, the narrowly funnelform tube glabrous, the ovate 1 -nerved membranous lobes 1.1-1.3 mm, thinly villosulous dorsally; filaments pink, at base connate through 0.5 mm or more around the ovarian stipe, exserted ± 10 mm. Pods solitary ascending subsessile, in profile broadly linear-oblong obtuse 45-5 5 x 11-13 mm, abruptly cuspidate by a beak 3-5 mm, the replum 1-5 mm wide, the valves firm, when dry ±0.4 mm thick in section, low-convex over each of 7- 10 seeds, together with replum densely villosulous and thinly glandular-setulose overall, when ripe separating from replum entire; seeds in broad profile ±6x4 mm, the testa fuscous-castaneous, brightly lustrous.

Distribution and Ecology - On stream-bank in campo, probably near or above 1000 m, known only from the type-locality on the w. slope of Chapada dos Veadeiros, near 14°10'S in e.-centr. Goiás, Brazil.—Fl. IX- X(-?).

Discussion:

Mimosa rhodostegia resembles M. regina in enlarged connate stipules, a character unique to these sibling species of ser. Pachycarpae. I am apprehensive about describing from single collections two species so clearly related, for new samples may very well devaluate some characters that at present appear sharply diagnostic. The differences in pubescence may prove illusory, but the stature of the plants, the differing texture and venation of the stipules, and different size of capitula and flowers cannot be passed over. It is noteworthy that M. rhodostegia and M. regina were collected in like stages of early anthesis at different seasons of the year, the former in late September, at the beginning of the wet season, the latter in late March, at the outset of the dry season. They may be differentiated in their life-cycles as are M. melanocarpa and sympatric forms of M. setosa. Further observation of these strangely modified mimosas is required.

Distribution:Brazil South America| Goiás Brazil South America|

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