Mimosa orbignyana Barneby

Margoth Atahuachi, M. Leontien Van Der Bent, John R. I. Wood, Gwilym P. Lewis & Colin E. Hughes, 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 (díOrbigny 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, Boliviaí 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 Guimar„es 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.

Figures

FIGURE 1. Chloroplast phylogeny of Mimosa. A. 50 % majority-rule consensus tree based on Bayesian analysis of 382 trnD - trnT noncoding plastid sequences. Numbers above branches are posterior probability values. The major clades proposed by Simon et al. (2011) are indicated with letters and sizes are proportional to the number of accessions included. B. Detail of clades containing new species here described from Bolivia and other newly generated sequences of species of doubtful identity are highlighted in grey.

FIGURE 6. Mimosa orbignyana. A. Habit and flowering shoots; B. Stipules; C. Leaflets; D. Floral bracts; E. Flower; F. Longitudinal section of flower, all from J. R. I. Wood et al. 26772 (LPB, K). Drawn by Rosemary Wise.

FIGURE 7. Mimosa orbignyana. A. Habit; B. habitat; C. multiple stems from base resprouting after fire; D. leaves; E. indumentum; F. inflorescences. All from L. Borges 787 (UB), Serranía Huanchaca. Photos by Leonardo Borges.