BIOLOGY OF LEAF MARK POLYMORPHISM IN TRIFOLIUM-REPENS-L .1. DISTRIBUTION OF PHENOTYPES AT A LOCAL SCALE

The distribution of the white leaf mark polymorphism of T. repens L. was studied in a lowland pasture in North Wales and in a series of 1 m2 quadrats elsewhere in Britain. Each quadrat was subdivided into 10 .times. 10 cm quadrats to allow the study of pattern. The number of morphs found in a 10 cm square was in the range 1.5-6.0 with a mean value of 4.16. In a 5 yr old seeded ley, the mean was 2.75. The populations consisted of a large number of morphs intimately mixed. The frequency distribution of morphs per quadrat differed from the frequency distribution of species, suggesting that some selective force operated to prevent any morphs from dominating the sward even on a local scale. The frequency of morphs bearing leaf marks decreased with increasing grass length suggesting a relationship with grazing. There was a seasonal pattern in the expression of the leaf mark phenotypes and the floristic diversity of such a pasture was represented at 3 levels: the species present, the genotypes present within each species and the various phenotypic expressions of these genotypes.