No sex at all? Extremely low genetic diversity in Gagea spathacea (Liliaceae) across Europe

Most vascular plant taxa are able to reproduce vegetatively in addition to sexual reproduction. Some plants even survive despite of (near to exclusive) sexual sterility. However, very few of these taxa are non-apomicts with a wider distribution range.Here we present the rare case of a virtually sexually sterile, non-apomictic plant, which was able to colonise its Central European range solely by clonal multiplication of a single genotype via subterranean bulbils: the geophyte Gagea spathacea (Liliaceae) occurs in forests in northern Germany and adjacent southern Scandinavia, with scattered populations spread all over Central Europe; recently the species was recorded from the Caucasus. We used AFLP fingerprinting to genotype 138 samples from 52 populations throughout this range. The analyses revealed an extremely low genetic diversity (simple matching distances 0–0.1353). By using a threshold for clone identity of <0.02, 136 of 138 samples were assigned to a single clone, the two deviating plants originated from one German population and from the Caucasus. The “megaclone” was present in all analysed Central European populations. A subset of 22 plus four additional populations was studied by DNA sequencing of the ITS region and of psbA-trnH IGS; these sequences were also found to be highly uniform.The absent spatial genetic structure throughout the species’ range lends strong evidence that G. spathacea is a sexual sterile, nearly monoclonal taxon. Most probably this can be explained by either the high ploidy level (nonaploidy) and/or the assumed hybridogeneous origin of this taxon. However, the purely clonal state with bulbils as sole means of dispersal poses further questions concerning species’ origin and putative colonisation history.