Monographs Details: Mimosa hypnodes 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 hypnodes Barneby
Synonyms:Mimosa adenotricha Benth., Mimosa somnians Humb. & Bonpl. ex Willd., Mimosa somnambulans Barneby
Description:Species Description - Weak shrubs or subshrubs 6-15 dm, the stems and axes of lvs and inflorescence variably pilose with erect rufous plain setae to 1-2.5 mm and viscid-setulose with fuscous gland-tipped trichomes to 0.3-1.3 mm often mixed with minute whitish villi, some internodes often and some lf-stks occasionally armed with scattered erect or subdecurved vulnerant aculei to 1.5-3.5 mm, the pallidly glaucescent foliage glabrous except for random cilia on some lfts proximal to pulvinus, the pseudoracemose inflorescence of small, rather loosely few-fld capitula exserted from foliage only at early anthesis, leafy in fruit. Stipules lanceolate or narrowly lance-setiform (3-)4-8 x 0.51 mm, plane or subinvolute, firm but not coriaceous, dorsally pubescent like stem, tardily deciduous. Leaf-stalks of major cauline lvs 3-13 cm, the petiole including little-dilated pulvinus 1.5-3.5 cm, at middle 0.5-1.2 mm diam., the longer interpinnal segments 10-25 mm, the ventral groove interrupted between pinna-pairs by an acicular spicule 0.6-1.5 mm; pinnae (2-)3-6- jug., moderately accrescent distally, the rachis of longer ones 2-5.5(-6) cm, their longer interfoliolar segments 1.5-3 mm; lfts of longer pinnae (8-)9-19-jug., a little decrescent at each end of rachis, the first pair 1-1.5 mm distant from subulate purplish paraphyllidia, all in outline oblong obtuse, the larger ones to 8-13 x 1.8-3.3 mm, the blades nerveless above, prominulously 3-nerved beneath, the midrib giving rise on each side upward from near middle to 4-5 secondary venules. Peduncles 1-3 per node, (1—) 1.5—4 cm; capitula without filaments 4-6 mm diam., prior to anthesis either conelike or moriform; bracts narrowly (ob)lanceolate 1-3.5 mm, dorsally either viscid-villosulous or subglabrous; flowers 4-merous 8-androus, the lowest staminate, the upper bisexual and a little larger; calyx 0.35-0.4 mm glabrous, or the rim with a few chaffy cilia to 0.2-0.4 mm; corolla 2.6-3 mm, the turbinate-campanulate tube glabrous, the ovate lobes ± 1 mm, faintly penniveined, dorsally either glabrous or thinly pilosulous. Pods (Anderson 6839, NY) 1-4 per capitulum, in profile 30-40 x 3-3.5 mm, cuneately narrowed at base into a stipe less than 1 mm, acuminately attenuate beyond the furthest seed into an erect beak, the replum 0.4-0.5 mm wide, undulately depressed between the 5-8 seeds, the papery valves bullately elevated over each seed, breaking up when ripe into free-falling articles 3-4 mm long and as or a little less wide, the pericarp and replum alike hispid and viscidulous with weak erect plain setae to 1-2 mm and shorter gland-tipped setulae mixed with fine villi; seeds (few seen) plumply rhomboid-ovoid ±2.8 x 2.5 mm, the testa lustrous castaneous.

Distribution and Ecology - On rocky hillsides in cerrado, 600-700 m, apparently uncommon, known only from e. affluents of upper rio Tocantins (forks of rios Manoel Alves and Paranã) between 11°30' and 13°30'S in centr. Goiás, Brazil.—Fl. II-IV(-?).

Discussion:

Between March 11 and 13, 1973 Dr. W. Anderson and companions collected within a few kilometers of Monte de Alegre de Goiás five mimosas referable to one or other of Bentham’s series Asperatae and Somniantes (all NY): no. 6833, typical prickly M. (Asperatae) adenocarpa, with tiny, indistinctly costate leaflets, 1-nerved corolla-lobes and short-stipitate pods; no. 6812, typical unarmed M. (Somniantes) somnians var. leptocaulis, with equally small but dorsally venulose, subglaucescent leaflets, pluristriate corolla-lobes and long-stipitate pods; no. 6892, type of M. somnambulans, resembling the last except for much larger leaflets (fruit unknown); and nos. 6839, 6907, here named M. hypnodes, in which the venulose leaflets of M. somnambulans coincide with aculeate stems, delicately 4-nerved corollas and the short-stipitate pods of M. adenocarpa. The two collections of M. hypnodes have the same foliage but differ in details of inflorescence, no. 6839 having the short bracts, glabrous corollas and pods exactly of M. adenocarpa, and no. 6907 longer bracts and pilosulous flowers foreign to all the rest but suggestive of widespread M. paludosa, probably present in the same region. The odd assortment of flowers, bracts and pods encountered in these collections are of a sort that might have arisen from hybrids between M. somnians and M. paludosa, but there is this difficulty: the large, dorsally venulose leaflets common to M. somnambulans and M. hypnodes, which differ from one another so greatly in venulation of the petals, occur in none of the three widespread species which could be supposed to furnish the other variable features. I am consequently obliged, though with reluctance, to describe M. somnambulans and M. hypnodes in the rank of species. If a distinction between striate-nervulose and membranous corolla cannot be upheld as significant, the taxonomy of the Asperatae will founder.

Beside Anderson’s two collections I have seen only one other of M. hypnodes, a flowerless plant collected on a tributary of rio Manoel Alves (rio Reason) by Pohl in July 1819, on his journey northward from São Felix to Porto Real (K, NY, W). This collection was tentatively referred by Bentham to a variety of M. elliptica.

Distribution:Brazil South America| Goiás Brazil South America|

Narratives:Mimosa hypnodes