Two species of rye-grass commonly occur in the UK: Italian Rye-grass (Lolium multiflorum) and perennial rye-grass (Lolium perenne).
Perennial rye-grass rarely occurs as a serious weed in UK arable crops, except after rye-grass seed crops, whereas Italian rye-grass is an increasing problem, especially in autumn-sown crops.
Distribution of Italian and perennial rye-grass based on 10 x 10 km grid records in the Atlas of the British Flora (2002).
Source: The New Atlas of the British and Irish Flora. C. D. Preston, D.A. Pearman and T.D. Dines, 2002 (Oxford University Press)