Polyploidy and habitat differentiation in Deschampsia cespitosa

The chromosome numbers of 114 populations of the Deschampsia cespitosa (L.) Beauv. complex, widely distributed in the British Isles, were determined from root-tip squash preparations. This revealed two widespread morphologically cryptic chromosomal races of seminiferous D. cespitosa (2n= 26, 52). The tetraploid is found throughout Britain; its range of habitats includes meadows, pastures, woodland, plantations, verges and waste ground. This is the first report of an extensive geographical distribution for tetraploid seminiferous D. cespitosa. The diploid appears to be mainly restricted to woodland, of mostly ancient, semi-natural origin. Populations with both chromosome numbers are rare. The tetraploid is usually found where invasive colonization has clearly occurred. The closely related proliferous taxon, D. alpina (L.) Roem. & Schult., was tetraploid, in agreement with published data. The prolifery itself induces changes in floret morphology. The floral morphology and cytological data together suggest that sub-specific rank is appropriate for this variant in British material.