Monographs Details: Mimosa oligosperma 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 densa Benth., Mimosa claussenii Benth.
Description:Species Description - Unarmed shrubs of unrecorded stature, sometimes of diffuse habit ("espalhado"), with slender cinnamon-brown annotinous branchlets ±3-6 mm diam. and lvs crowded toward branch-tips, the young shoots and lf-stks densely hispid with ascending attenuate setae to ± 2-3 mm, at dilated base 0.2-0.3 mm diam., glandular (if at all) only on floral bracts, the brownish-olivaceous foliage concolorous, the firm plane lfts mostly glabrous lustrous on both faces, the proximal ones of some pinnae thinly setose dorsally, all densely setose-ciliate, the axillary peduncles forming a short pseudo-corymb of globose capitula surpassed by lvs. Stipules firm triangular-lanceolate 4-7 x 2-3 mm, dorsally setose like stem, glabrous castaneous within, deciduous. Leaf-stalks 4-9 cm, the petiole including obese pulvinus 2-12 x 1.1-1.6 mm, the interpinnal segments 4-8 mm; spicules 0; pinnae of longer lvs 10-12-jug., decrescent proximally, the rachis of longer distal ones 2.5-4cm, the longer interfoliolar segments 0.6-1 mm; lfts of longer pinnae 28-40-jug., subequilong except at ends of rachis, the first pair close to pulvinus (paraphyllidia 0), all in outline narrowly lance-oblong from proximally obtusangulate base, obtuse or acute, the longer ones (3-)3.5-6 x 0.8-1.2 mm, 3.8-5 times as long as wide, all when mature externally veinless or very obscurely centri-costate. Peduncles solitary (2-)2.5-6 cm; capitula without filaments ±11 mm diam.; bracts linear-oblanceolate or -elliptic 2.5-4.5 x 0.5-1.1 mm, on back densely setose and sometimes also glandular-setulose, either glabrous or puberulent ventrally; flowers 4-merous 8-androus; calyx-tube shallowly campanulate 0.3-0.5 mm, its subtruncate rim ciliate with fine stramineous setae to ± 1 mm; corollas narrowly funnelform, those at and above mid-capitulum 4.5-5 mm, the tube glabrous, the ovate acute thin-textured lobes 1.3-1.6 x 0.9-1 mm, silky-setulose dorsally; filaments united at very base, exserted ± 8 mm. Pods 1-few per capitulum, in profile elliptic or oblong-elliptic 14-20 x 9-12 mm, less than twice as long as wide, 4-5-seeded, the replum 1-2.5 mm wide, produced into a very short cusp, the firm valves falling entire from replum, the livid exocarp 0.2-0.4 mm thick in section, the replum and valves alike densely setose with erect-incurved subcontiguous setae to 2-2.5 mm long, at base 0.2-0.5 mm diam. and commonly there stellately branched; seeds plumply ovoid-lenticular 4.2-5.2 x 3.5-4.2 mm, the testa light brown lustrous.

Distribution and Ecology - In unrecorded habitat, to be expected in campo rupestre or about sandstone outcrops near and above 1000 m, known only from s.e. tributaries of rio Tocantins between Cavalcante and Niquelândia, near 13°45'-14°30'S in centr. Goiás, Brazil.—Fl. season not established.

Discussion:

Mimosa oligosperma seems closely related to M. densa and its relatives, all of which could be envisaged as detached vicariant offshoots of one comprehensive species-complex. It differs from all these in a very small few-seeded pod, and from M. densa, a near neighbor on the southern spurs of Chapada dos Veadeiros and Chapada do Paranã, in somewhat longer pinnae and slightly larger leaflets and flowers. The only modem collection of M. oligosperma known to me (Macedo 3633, NY) is described by the collector as arbusto espalhado da serra, all that we know at present of the plant’s habit or stature.

The type and paratype of M. oligosperma were referred by Bentham to a broadly conceived and highly polymorphic M. claussenii.

Distribution:Brazil South America| Goiás Brazil South America| Tocantins Brazil South America|