Variation in the colour of the keel petals in lotus corniculatus L. 4. Morph distribution in the British Isles

Abstract

Keel-petal colour (dark versus light) in Lotus corniculatus L. has been scored for 125, 503 plants at 1348 sites throughout the British Isles. The polymorphism shows strong and regular clinal change in morph frequencies. In all areas of western Britain and in southern England the majority of plants has light keels, particularly so in coastal regions. In eastern England, north of the River Humber, and in eastern Scotland dark-keeled plants predominate. Most off-shore islands conform to this pattern. Although the range in morph frequencies is virtually complete, monomorphism is unusual except in small samples, suggesting frequency-dependent selection in favour of the dark-keeled morph when rare. At least in Yorkshire, dark-keeled plants are under-represented in the early stages of the flowering season; this is of doubtful evolutionary significance, although it is important in terms of sampling. © 1988, The Genetical Society of Great Britain.