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Department of Botany, Faculty of Science, Tanta University, Tanta, Egypt and Department of

Botany, Faculty of Science, Mansoura University, Mansoura, Egypt

ABSTRACT

The present study analyses the vegetation along the irrigation and drainage canals in Al- Hassa Oasis, Eastern Saudi Arabia. A total of 98 plant species were recorded. The annuals decrease, and the biennials and perennials (many are rhizomatous) increase along the moisture gradient from the terraces to the free-water zone. This appears to be correlated, at least partly, with the instability of the substratum along the banks. Twelve vegetation clusters were identified after application of the TWINSPAN procedure. The most important are the cluster characterized by Suaeda aegyptiaca, Phragmites australis and Salsola vermiculata, and that dominated by Phragmites australis. The identified vegetation clusters were compared with the plant communities of the irrigation and drainage canals in the Nile Delta region.