Species of Cyperaceae and Restionaceae were examined for presence of vesicular-arbuscular (VA) mycorrhizal fungi in natural habitat in south-west Western Australia. VA mycorrhizal fungi were detected in roots of two species of Cyperaceae (Lepidosperma gracile and Tetraria capillaris), and two species of Restionaceae (Alexgeorgea nitens and Lyginia barbata), all representing the first records for these genera. Results indicated a very short seasonal period of infection, with VA mycorrhizal fungi representing the genera Acaulospora, Glomus, Scutellospora and Gigaspora identified in roots. VA mycorrhizal fungi were prominent from late autumn to early winter (April-June) and in up to 30% of the young, new season's roots as they penetrated the upper 10 cm region of the soil profile. Mycorrhizal infection was not evident during the dry summer months. This study suggests that mycorrhizas may be important for nutrition of these hosts in these environments but their activity is restricted to a brief period of the growing season.