A New Mascarene Sesuvium (Aizoaceae)

Abstract

Dr. Philip B. Ayres (1813-1863), while serving in the Mauritian Civil Service, intended writing a Flora of Mauritius. It was he who first recognized the Sesuvium described below as a new species, which he intended to call S. ovatum. Baker, in his Flora of Mauritius and the Seychelles, treated this plant as S. portulacastrum (L.) L., ignoring Ayres' detailed description and the name on his specimen at Kew. During the course of preparing an account of the Aizoaceae for the Flore des Mascareignes it was possible to distinguish the Mascarene plant from the almost pantropic S. portulacastrum. The following description is based largely on a manuscript description by Ayres in the library of the Sugar Industry Research Institute, Mauritius, and on notes by H. H. Johnston in his copy of Baker's Flora of Mauritius and the Seychelles now at the Royal Botanic Garden, Edinburgh. The seven gatherings not seen by Ayres show considerable variation in leaf-shape, and his original epithet 'ovatum' is no longer entirely apt. Whether this variation is in part due to the degree of salinity of the habitat should be studied in the field. Johnston also lists sight records for the species from Ile au Fouquets, Ile Vacoas, Ile aux Fous, Rocher des Oiseaux, and Ile aux Benitiers. Almost all the labels giving information indicate that the species is confined to 1 5-7 m above sea level, on coral rocks, exposed to salt spray. The exception is the type whose label states 'on sand surrounding salt-water pools near Fort William'.