First insights into weed communities of rice agrocoenoses in southern Thailand

The study presents the results of geobotanical investigations conducted in rice fields in southern Thailand in 2013. It is focussed on the classification of plant communities poorly investigated from a geobotanical standpoint. Altogether 125 phytosociological relevés were collected, using the Braun-Blanquet method. We noted more than 100 species in the vegetation plots, including many rare ones. We classified the vegetation into seven communities, including six associations. Five associations are proposed as new: Nymphaeetum nouchali, Fimbristylido miliaceae-Sphenocleetum zeylanicae, Ischaemo rugosi-Cyperetum pulcherrimi, Pentapeto phoeniceae-Aeschynomenetum indicae and Marsileetum minutae. The distinctiveness in species composition compared to other Oryzetea sativae phytocoenoses justifies a new alliance: Ludwigion hyssopifolio-octovalvidis. The main discrimination factors for the data set were water depth and species richness. The study reveals that rice paddy fields are inhabited by a variety of littoral and aquatic vegetation types. In particular, non-intensively cultivated rice fields hold a diverse hydrophilous flora, especially taxa typical for mud or littoral habitats.