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

Abstract

The terrestrial vascular plant diversity of the Iles Eparses was widely underestimated until the end of the 20 th century. Thanks to numerous inventories (578 days from 2004 to 2016) conducted by the Conservatoire Botanique National de Mascarin (CBNM) on the flora of the Iles Eparses we now have new information on the presence of 237 taxa (123 native, 100 alien and 14 cryptogenic) belonging to 62 families and 173 genera. This represents an increase of 42-340% for the various territories. The flora of Europa [30 km 2 ] includes 94 taxa in 34 families (47 native, 39 alien and 8 cryptogenic), that of Juan de Nova [5 km 2 ] 147 taxa in 49 families (66 native, 69 alien and 12 cryptogenic), that of the Glorioso islets [4.37 km 2 ] 123 taxa in 49 families (72 native, 49 alien and 2 cryptogenic) and that of Tromelin [1 km 2 ] only 20 taxa in 17 families (6 native, 13 alien and 1 cryptogenic). The native plant diversity per km 2 is lower for Europa (1.56) and Tromelin (6) and highest for Juan de Nova and the Glorioso islets (13.2 and 16.5, respectively). In comparison with the Aldabra group, the Iles Eparses almost have the double native plant diversity per km 2 (1.53 and 3, respectively). The native vascular floras of Europa, Juan de Nova and the Glorioso islets are mainly characterized by pantropical (24-31%) and Indo-Pacific taxa (12-19%) In Juan de Nova and Europa, the Malagasy elements sensu stricto are strongly represented (12-15%), while taxa in the Glorioso islets are confined to the West of the Indian Ocean (29%). Only Europa and Juan de Nova seems to host local endemics species ( Achyranthes sp.3, Amaranthaceae, and Euphorbia sp.1, Euphorbiaceae, on Europa; Hypoestes juanensis Benoist, Acanthaceae, on Juan de Nova), while Perrierophytum glomeratum Hochr., Malvaceae found both on Juan de Nova and the Glorioso island is endemic to the Mozambique channel. The alien floras of Europa, Juan de Nova and the Glorioso islets include 58-84% naturalized alien taxa while that of Tromelin hosts 54% of non-naturalized alien taxa. The majority of cultivated alien taxa are found in Juan de Nova and Tromelin (56% and 77%), respectively.