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Germplasm of the perennial pasture grass Phalaris aquatica L., from Sardinia, Italy, is a potentially valuable source for grass breeders owing to climatic similarities to regions where P. aquatica is used, a relatively high incidence of acidic soils, and exposure to prolonged grazing pressure. At field sites in south-eastern Australia, Sardinian accessions were compared as spaced plants and drill-rows with accessions from southern Europe and north-western Africa and with commercial cultivars. They were also evaluated in grazed swards at three sites over 4 years under conditions that challenge persistence, including heavy grazing pressure, acid soils and drought. Morphologically, the accessions were comparatively dense, fine and short, with similarities to southern European accessions and cultivars of the cv. Australian type. However, they were earlier heading and more summer-dormant, particularly those from southern Sardinia. In drill-rows, Sardinian accessions were later heading and less productive in winter than accessions from Morocco. In swards, Sardinian accessions had lower seedling vigour and winter growth potential than modern winter-active cultivars. However, they were dense and persistent under high grazing pressure, and some accessions survived better than all cultivars on an acid, low-fertility soil. Developing cultivars that are superior to the cv. Australian type with acceptable seed production and alkaloid levels presents a challenge to breeders. However Sardinian germplasm offers a range of maturity times combined with higher levels of summer dormancy and a grazing-tolerant morphology, attributes that may expand the area of adaptation of the species into the hotter and more drought-prone margin. Germplasm of Phalaris aquatica from Sardinia is a potentially valuable source of grass cultivars for livestock production in regions that experience dry summers. Accessions from Sardinia displayed lower seedling vigour and winter growth than modern cultivars but were denser and more persistent under high grazing pressure and had good spring production, and some accessions survived better on difficult soils. The germplasm displayed attributes that could help livestock industries facing multiple stresses in the future. [ABSTRACT FROM AUTHOR]