Monographs Details: Mimosa amnis-atri 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 gemmulata Barneby
Description:Species Description - Unarmed, elaborately microphyllidious shrub with several stout, obliquely erect, densely foliate simple stems ± 1.5 m, near middle 4-7 mm diam., passing upward into a pseudoraceme of long amentiform fl-spikes exserted in early anthesis 2-4 dm beyond coevally expanded lvs but probably hysteranthously leafy, the upper stems, lf-stks and axes of inflorescence pilosulous with erect or ascending yellowish hairs to 0.25-0.6 mm intermixed with scattered sessile spherical golden glands ±0.1 mm diam., the minute crowded plane-margined lfts bicolored, above brown glabrous, beneath thinly pilosulous and golden-glandular, finely ciliolate. Stipules subulate 2-2.5 x 0.2-0.3 mm, persistent. Leaf-stalks of major lvs 6-12.5 cm, the petiole no longer than the dilated pulvinus, the longer interpinnal segments 2-2.5 mm, the ventral groove interrupted between most or some distal pairs of pinnae by a minute stramineous spicule; pinnae 35-49-jug., of subequal length or slightly decrescent distally, the rachis of longer ones 7-18 mm, the longer interfoliolar segments 0.3-0.5 mm; lfts of longer pinnae 20-26-jug., very slightly decrescent distally, the first pair close to subulate paraphyllidia, the blades oblong or elliptic-oblong from obliquely truncate base, obtuse at apex, the longest 1.2-1.6 x 0.45-0.6 mm, all faintly costate dorsally but otherwise externally veinless. Spikes solitary or geminate, the axis including peduncle 8-15 cm; bracts lanceolate 0.3-0.6 mm; fl-buds subglobose; flowers 4(-5)-merous 8(-10)-androus, many functionally staminate with abortive pistil; calyx shallowly campanulate ±0.7 mm, the teeth 0.3-0.4 mm, separated by broad sinuses; corolla pink-cream, broadly turbinate in profile, 1.5-1.9 mm, the ovate subacute 1-nerved lobes 0.7-0.9 x 0.6-0.9 mm, thinly puberulent and gland-sprinkled dorsally; filaments pink, free, the longer ones exserted 5-6 mm; ovary thinly pilosulous; pod unknown.

Distribution and Ecology - In cerrado on summit of a chapada at 1000 m, known only from the type-locality close to the Goiás-Minas boundary at 16°5'S, 46°45'W.— FL XI-I(-?).—‘Guarapauá’ of Irwin’s field-book and labels probably = Garapuava of maps.

Discussion:

While I entertain no doubt as to the close affinity of M. amnis-atri to M. gemmulata, I am uneasy about its status as a distinct species. The long narrow leaves composed of very numerous, crowded pairs of abbreviated pinnae furnished with as many as 20-26 pairs of minute crowded leaflets are visually arresting, but could be interpreted as an extreme modification within M. gemmulata sensu lato. Reassessment of its taxonomic rank is best postponed until the fruit becomes known.

Distribution:Brazil South America| Goiás Brazil South America| Minas Gerais Brazil South America|