The lilioid herb, Anthericum ramosum, occurs in four geographically-isolated regions (Sjaelland, Skane, Oland and Gotland) in Denmark and southern Sweden. We investigated allozyme variation at nine polymorphic loci in A. ramosum from 16 sites (33 populations) in the four regions. There was no clear overall geographic pattern of differentiation between the regions, but the southernmost Gotland and the Oland populations had similar allele frequencies, suggesting that they have had a common history. the total genetic diversity (H-tot) wa 0.458 and the between-region, site- and population components of diversity accounted, respectively, for 13%, 10% and 2% of the total diversity. The species is restricted to grassland habitats. Such habitats have become increasingly rare in the Sjaelland and Skane regions, where A. ramosum now has a highly fragmented distribution. Within three of the regions (Sjaelland, Skane and Oland) there was a negative relationship between the extend of grassland habitat and the between-site components of genetic diversity. Oland, with its extensive grassland habitats and low levels of population disjunction, showed little allelic differentiation between sites and the lowest between-site component of diversity (3%), suggesting that there is (or has been) extensive gene flow between sites. The between-site components of diversity were higher within Skane (7%) and Sjaelland (12%). The high within-region G(ST) (25%) for the fourth region, Gotland, cannot be explained in terms of recent habitat disjunction but is, instead, interpreted in terms of the restricted distribution of limestone bedrock on Gotland and the fact that the southern and northern Gotland populations appear to have had different origins. (C) 2000 Linnean Society of London.