Monographs Details: Mimosa somnambulans 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 somnians Humb. & Bonpl. ex Willd.
Description:Species Description - Slender, openly branched, distantly but amply leafy shrubs to 2.5 m, the smooth terete branches and lower lvs glabrous, the stems distally, peduncles and axes of paniculate, well-exserted inflorescence viscid-hispidulous with fine gland-tipped setulae 0.2-0.7 mm, the lfts mostly quite glabrous, rarely remotely ciliolate, the globose capitula as in M. somnians sensu lato. Stipules stiffly erect, narrowly lance-attenuate 4-7 x 0.51 mm, mostly 3-5-nerved, glabrous dorsally, ciliolate. Leaf-stalks of lvs below panicle 8-11.5 cm (some distal lvs shorter, no further described), the petiole 4-5.5 cm, at middle 0.6-0.9 mm diam., the longer interpinnal segments 2-4.5 cm; a spicule 0.4-1.5 mm between each pair of pinnae; pinnae (2-)3-4-jug., the rachis of longer ones 5-10 cm, the longer interfoliolar segments 2-4 mm; lfts of longer pinnae 18-34-jug., in outline oblong obtuse from inequilaterally rounded base, the larger ones 12-17 x 2-4.5 mm, all 4-6-nerved from pulvinule, the midrib subcentric, giving rise on each side to (3-)4-5 narrowly ascending secondary venules, the anterior primary nerve submarginal and produced almost to blade apex, the outer posterior ones shorter, all slenderly prominulous dorsally. Peduncles mostly 2-3 per node, 12-18 mm; capitula without filaments ±4.5 mm diam., prior to anthesis moriform; bracts membranous obovate-elliptic 0.5-0.9 mm, remotely ciliolate, 1 -nerved; flowers 4-merous 8-androus glabrous, the staminate proximal ones a little smaller than the bisexual distal ones; calyx campanulate subtruncate 0.4 mm; corolla turbinate 1.7-2.4 mm, the ovate obtuse, shallowly concave, striately venulose lobes 0.7-1.1 mm; filaments pink, free, exserted 4-5 mm; pod and seed unknown.

Distribution and Ecology - About granitic outcrops in mesophytic forest at ±600-800 m, known only from steep slopes of Sa. da Atalaia near 13°20'S, 47°20'W in e.- centr. Goiás, Brazil.—Fl. II-IV(-?).

Discussion:

The affinity of M. somnambulans to M. somnians expressed in similarity of habit, foliage and floral structure is so close that the only question confronting the taxonomist is the rank to which it is entitled. Because the plant is unarmed but glandular-setulose, it is best compared with M. somnians var. leptocaulis. The ample leaflets, which are more than twice the size of any encountered among the multitudinous races of var. leptocaulis (or elsewhere in M. somnians) and as a consequence more elaborately venulose, together with stipules narrower and fewer-veined and a more diffusely branched and further exserted panicle of pseudoracemes contribute to a strongly individual facies. I provisionally evaluate M. somnambulans as standing outside the orbit of its racially complex relative (and likely precursor) M. somnians, and suppose it to be a microspecies recently derived by saltatory evolution from it.

Distribution:Brazil South America| Goiás Brazil South America|