An Updated Account of the Vascular Flora of the Iles Eparses (Southwest Indian Ocean)

The terrestrial vascular flora of the Iles Eparses (southwest Indian Ocean) was widely underestimated until the end of the 20th century. Thanks to recent field surveys and plant inventories conducted between 2004 and 2017 by the Conservatoire Botanique National de Mascarin (CBNM), a total of 250 taxa (120 native, 107 alien and 23 cryptogenic) belonging to 66 families and 178 genera, was recorded. This represents an increase of 42-313% for the four surveyed islands. While Bassas da India does not show any terrestrial flora, the flora of Europa includes 94 taxa (47 native, 39 alien and 8 cryptogenic), that of Juan de Nova 147 taxa (62 native, 69 alien and 16 cryptogenic), that of the Iles Glorieuses 137 taxa (67 native, 61 alien and 9 cryptogenic) and that of Tromelin only 21 taxa (7 native and 14 alien). The native plant species density is lower for Europa (1.56/km²) and Tromelin (7/km²) and highest for Juan de Nova and the Iles Glorieuses (12.4/km² and 15.3/km² respectively). The native vascular floras of Europa, Juan de Nova and the Iles Glorieuses are mainly characterized by pantropical (24-30%) and Indo-Pacific taxa (13-22%). In Juan de Nova and Europa, the Malagasy elements sensu stricto are strongly represented (13-15%), while taxa in the Iles Glorieuses are confined to the southwest of the Indian Ocean (30%). Europa, Juan de Nova and Tromelin seem to host local endemics species while one taxon found both on Juan de Nova and Grande Glorieuse is endemic to these two islands. The alien flora of Europa, Juan de Nova and the Iles Glorieuses comprise between 64% and 97% naturalized taxa while that of Tromelin hosts 50% of non-naturalized alien taxa. The higher percentages of cultivated alien taxa are found in Juan de Nova and Tromelin (56% and 71%, respectively).