The Distribution of Chromosome Races of Ranunculus ficaria L. in the British Isles

Abstract

The chromosome numbers of 889 plants from 222 British populations of Ranunculus ficaria were counted. 66.1 per cent of the populations contained diploids (49.1 per cent of plants), 4.1 per cent contained triploids (5.5 per cent of plants) and 43.2 per cent tetraploids (45.4 per cent of plants); 13.1 per cent of the populations contained two or more polyplotypes. At the fruiting stage, tetraploid plants can be reliably distinguished from diploids by the presence of axillary bulbils in the tetraploids and their absence in the diploids. The production of well-developed heads of achenes, which is more characteristic of the diploids than of the tetraploids, is a less reliable character. Diploid plants are widespread throughout the British Isles but tetraploids are more common in the east than in the west; 17.6 per cent of the diploid plants had B-chromosomes and these plants were virtually confined to southern England and the Midlands. The occurrence of triploids and of mixed populations of diploids and tetraploids are both shown to be more common than previously supposed.