Mimosa orbignyana Barneby, 1991

Atahuachi, Margoth, Bent, M. Leontien Van Der, Wood, John R. I., Lewis, Gwilym P. & Hughes, Colin E., 2016, Bolivian Mimosa (Leguminosae, Mimosoideae): three new species and a species checklist, Phytotaxa 260 (3), pp. 201-222 : 216

31. Mimosa orbignyana Barneby

This species has remained poorly understood, known only from the type collection (d’Orbigny 743 P, Bolivia, Chiquitos, August 1831), and apparently never re-collected since, until very recently. It was described by Barneby (1991) as ‘in unknown habitat, but to be sought in campo or cerrado at or above 700 m on the Sierra de Santiago, near 18° 30´S in south-east Santa Cruz, Bolivia’ and has been considered endemic to Bolivia. Within the last two years, two collections, both from further north, on the Serranía Huanchaca have been made (J.R.I. Wood 26772, LPB, K, USZ, from the southwest part of the meseta of the Serranía Huanchaca in the Noel Kempf National Park in Bolivia, and L. Borges 787, UB, from the southern end of the Huanchaca range in neighbouring Mato Grosso in Brazil, where the range is known as the Serra do Ricardo Franco). However, despite extensive fieldwork in areas where d’Orbigny is likely to have visited in ‘Chiquitos’, no material matching this species has been re-collected from any of these areas. This is perhaps surprising, given that M. orbignyana forms a substantial shrub to 2 m height, multi-stemmed from the base, resprouting after fire from an underground woody root system that is much thicker than the above-ground stems, and with conspicuous 1–1.2 m tall efoliate pseudoracemes of bright pink flowers ( Figs. 6 & 7). Barneby (1991) placed M. orbignyana in his ser. Setosae of sect. Habbasia and indicated likely affinities to M. riedelii Benth. from the Chapada dos Guimarães in Mato Grosso and M. aguapeia Barneby from the Serra do Aguapei also in Mato Grosso. These overall affinities are confirmed by analysis of a trnD -trnT sequence of M. orbignyana as sister to a clade comprising ser. Setosae and ser. Pachycarpae (clade O in Simon et al. (2011)) plus M. corynadenia ( Fig. 1). Although no sequence data are available yet for M. riedelii and M. aguapeia , the discovery of M. orbignyana in the Serranía Huanchaca confirms Barneby’s notion that these three potentially closely allied species occupy disjunct ranges on these ancient sandstone chapadas around the periphery of the upper Rio Paraguay basin.