In Western Australia - a relatively arid portion of the continent - wet environments are only occasionally vegetated, but well-developed communities occur in winter-wet habitats in sandplain depressions, along water courses and on rock (mostly) granite outcrops. These communities are composed of small-sized annuals, mostly belonging to the Centrolepidaceae, Asteraceae, Cyperaceae, Juncaginaceae, and Stylidiaceae. Multivariate analysis was carried out on 46 phytosociological relevés; four associations are recognized with a distinct floristic composition and ecology. Species occurring in this vegetation are mostly therophytes (66%) and many are endemics; a new vegetation class Centrolepidi-Hydrocotyletea alatae, endemic for Australia, is proposed and described.