Monographs Details: Mimosa orbignyana 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 riedelii Benth.
Description:Species Description - Unarmed, amply microphyllidious shrubs of unrecorded stature, the stems and lf-stks hispid-pilose with incurved-ascending, basally dilated, sordid scaberulous setae to ± 1.5 mm, mixed with minute puberulence but no gland-tipped setulae, the brunnescent foliage subconcolorous, the lfts thinly puberulent on both faces and some randomly strigose beneath, discontinuously finely setose-ciliate, the inflorescence a panicle of efoliate pseudoracemes 1-2.5 dm, each from a lf-axil, the peduncles densely silky-pilose with longer flagelliform, distally smooth setae. Stipules subcoriaceous erect triangular-lanceolate 4.5-6 x 1.5-2 mm, densely setose dorsally, glabrous within, disjointing in age. Leaf-stalks to 15 cm, the petiole including hard obese pulvinus ±8-12 x 1.5-2 mm, the interpinnal segments 5-8 mm, the ventral groove obscure; spicules 0; pinnae ± 17-21-jug., decrescent proximally, the rachis of longer ones 3.5-5 cm, the longer interfoliolar segments 1-2.5 mm; lfts of distal pinnae 18-21-jug., subequilong, the first pair less than 1 mm distant from pulvinus or from minute paraphyllidia concealed by setae, the thick-textured plane blades obliquely ovate-elliptic from broadly semi-cordate base, obtuse at apex, the longer ones 4.5-6.5 x 1.7-2.1 mm, 2.7-3.3 times as long as wide, all veinless above, beneath 1(- 2)-nerved from pulvinule, the midrib displaced to divide blade ±1:2, only weakly prominulous, the one posterior nerve short, faint or obsolete. Peduncles mostly geminate 1.5-3.5 cm; capitula subglobose, without filaments 9-10 mm diam., prior to anthesis conelike silky-pilose; receptacle densely setose; bracts linear-lanceolate 3.5-5 x 0.4-0.7 mm, densely setose and sparingly glandular-setulose dorsally from base upward, deciduous; flowers 4-merous 8-androus, mostly bisexual; pedicels to 0.3 mm, setose; calyx pappiform 2.7-3 mm, decompound to within 0.3 mm of base into fine setae; corolla funnelform 4—4.2 mm, the tube glabrous to middle, the ovate 1 -nerved, shallowly convex lobes 1-1.5 x 0.7-1 mm, setose-barbellate dorsally; filaments pink, monadelphous through ± 1 mm, exserted 5-6 mm. Pods (not seen fully ripe) several per capitulum subsessile, in profile undulately linear ±30-35 x 5 mm, 3-5-seeded, the shallowly constricted replum ±0.5 mm wide, densely hispid with slender vertical straight gland-tipped setae varying from 0.5 to 2.5 mm, the livid thin-textured valves likewise densely hispid but with partly plain setae, low-colliculate over each seed and transversely cracked between them, presumably breaking up into free-falling articles, these elliptic or quadrate 6-10 mm long; seeds unknown.

Distribution and Ecology - In unknown habitat, but to be sought in campo or cerrado at or above 700 m on Sa. de Santiago, near 18°30'S in s.-e. Santa Cruz, Bolivia.—Fl. VIII-IX(-?).

Discussion:

Bentham annotated the type of M. orbignyana as "Mimosa: Ameria Pachycarpae sp. nov.," but left it undescribed. Like M. riedelii, its analogue on the sandstone caprock of Chapada dos Guimaraes in Mato Grosso, M. orbignyana has the ample multifoliolate leaves and general aspect of ser. Pachycarpae, but the pods of both are thin-textured craspedia with relatively narrow replum and valves cracking between seeds even before full maturity. In this feature, and in the paniculate inflorescence and form of calyx, these two species seem more closely akin to M. setosa, although easily set apart by the scaberulous cauline setae and range of dispersal far distant to the west. While many common features denote a close relationship between M. riedelii and M. orbignyana, the differences in leaf-formula, in length of peduncles and in vesture of the pod, summarized in the diagnosis, are specifically distinctive.

The floristic relationship between Chapada dos Guimarães in Mato Grosso and Sa. de Santiago in Bolivia, situated respectively on the east and west periphery of the upper Paraguai basin, is further exemplified by the two species of Eumimosa, M. bipennatula and M. jacobita. The chapada and the sierra are remnants of ancient sandstone caprock perhaps once continuous across what is now the valley of rio Paraguay. The possibility of a link beween these isolated floras on the heights of Sa. do Aguapei, near the Brazil-Bolivia border at 16°S, cries for investigation.

Distribution:Bolivia South America| Santa Cruz Bolivia South America|