AbstractThe botanical composition of grass fields in Iceland was investigated during the years 1990-1993. The investigation included 1294 grass fields on 191 farms. More than 50 species were recorded. The most common species were Poa pratensis, Festuca rubra, Phleum pratense, Deschampsia caespitosa and Agrostis sp. Other common species were Poa annua, Alopecurus pratensis, Alopecurus geniculatus, Stellaria media, Ranunculus acris, Taraxacum spp., Cerastium fontamum and Rumex acetosa. The most important factors affecting the proportion of the species were region and age of the sward. Other important factors were soil type, soil moisture, winter kill, spring grazing, height above sea level, and distance from the sea.