Monographs Details: Mimosa vexans 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 vexans Barneby
Synonyms:Mimosa schrankioides Benth.
Description:Species Description - Weakly frutescent scrambling vine attaining 2.5 m, the stems and both dorsal and lateral ribs of lf-axes densely serially armed with recurved stramineous aculei to 1.5-2.5 mm and also hispid with fine spreading sordid setae about as long, the foliage green, the thin-textured lfts finely pilosulous ventrally, appressed-setose-strigose dorsally, discontinuously setose-ciliate, the globose capitula (so far as known) axillary to distal lvs. Stipules linear-setiform 3-6 x 0.3-0.5 mm, becoming dry deciduous. Leaf-stalks 6-9 cm, the petiole 5.5-8.5 cm, at middle 0.7-1.2 mm diam., the one interpinnal segment 5-12 mm; spicules apparently 0; pinnae 2-jug., the rachis of longer ones 3.5-7 cm, the longer interfoliolar segments 2.5-4.5 mm; lfts of longer pinnae 15-19-jug., the first pair 1.5-4 mm distant from subulate paraphyllidia to 1.5 mm, the blades narrowly oblong from asymmetrically rounded base, abruptly acuminulate at apex, the longer ones ±10-17 x 3-4 mm, 3.3-4.5 times as long as wide, all weakly 3-nerved from pulvinule, the midrib subcentric, simple or faintly branched, the inner posterior nerve scarcely attaining mid-blade, the outer one short and weak. Peduncles (solitary so far as seen but very likely paired or fasciculate when young) in fruit 20-24 mm; capitula (not seen at anthesis) without filaments probably ±5.5 mm diam., the receptacle ±2 x 1.5 mm, thinly setose; bracts linear, to 2 x 0.4 mm; capitula (not seen at anthesis) without filaments probably ±5.5 mm diam., the receptacle ±2 x 1.5 mm, thinly setose; bracts linear, to 2 x 0.4 mm, glabrous dorsally, 1-nerved, setose-ciliate above middle; flowers 4-merous, glabrous; calyx paleaceous-pappiform ±1.2 mm, the tube ±0.4 mm, the lobes deeply dissected; corolla ±2.3 mm, the cymbiform, dorsally keeled lobes ±0.7 x 0.5 mm; androecium not seen. Pods 1-10 per capitulum, sessile, in profile narrowly oblong 15-25 x 6-7 mm, abruptly cuspidate at apex, the almost straight replum ±0.4 mm wide, together with papery stramineous valves densely hispid overall with slender erect straight tapering setae to ±2-4 mm, the valves breaking up into almost square articles 5-6 mm long.

Distribution and Ecology - In secondary forest at 1000-1200 m, known only from the type-locality, at 10°15'N, 68°29'W in the state of Yaracuy, n.-centr. Venezuela.— Fr. III.

Discussion:

The mimosa described above is as vexatious from a purely tactile as from a systematic viewpoint. In habit, in armature, in flower and in fruit it closely resembles M. schrankioides var. schrankioides, but it differs from this species, and from all other Castae, in having two pairs of pinnae per leaf, the lower pair arising shortly below the terminal pair but not contiguously. The plant could be interpreted as a variety of M. schrankioides with anomalous foliage, but the question of its rank must be deferred until more can be learned about possible variation in leaf- formula. The late Dr. Julian Steyermark observed (pers. comm.) that the type-locality is in a region rich in local endemism.

Distribution:Venezuela South America| Yaracuy Venezuela South America|

Narratives:Mimosa vexans