Long-held fears of losing the beloved British bluebell species (Hyacinthoides non-scripta) through hybridisation with a rampant non-native may have been unnecessary. New research indicates the genetic threat to native plants from ‘Spanish’ bluebells is relatively minor – and has generally been aided by well-intentioned humans bulking-up plant populations. What’s more, say the scientists in the Royal Botanic Garden Edinburgh (RBGE) led study, the “invader” is not what we thought it was.

For centuries the British bluebell has shared habitats with non-natives, commonly referred to as ‘Spanish’ bluebells (Hyacinthoides hispanica) and a hybrid of the two. This has caused widespread speculation that – like the Scottish wild cat and the native wild apple – ongoing interbreeding could intermix the gene-pools to such an extent that pure British bluebells become extinct.

To understand the true nature of the potential threat, the new study set out to quantify the extent of hybridisation between the native and non-native species. But, the starting point had additional complications through taxonomic uncertainty over the exact identity of the non-native bluebells in the UK.

Genetic analyses of 501 bluebell samples from 56 populations around Britain and the Iberian Peninsula brought to light the fact that the non-native bluebells collected in Britain were not actually the ‘Spanish’ bluebell but a hybrid of it and the British species. Furthermore, Portugal, not Spain, was actually the country of origin of the first H. hispanica introductions to the UK.

Under closer examination, not only did hybrids make up just 16 per cent over the overall number studied but backcrosses between the hybrid non-native bluebell and the British species were primarily found in public parks. Of native bluebells sampled from natural habitats, only two per cent showed evidence of introgression - the transfer of genetic information back and forward from one species to another as a result of hybridisation.

Dr Markus Ruhsam, a molecular ecologist at RBGE and lead author on the research paper explained: “Although hybridisation might be frequent in locations where non-native bluebells have been introduced, we found no evidence of large-scale introgression in natural H. non-scripta populations.

“This might explain the widespread nature of the non-native hybrid in the UK. Rather than hybrid vigour and enhanced competitive ability, it is likely that planting of the non-native in private and public gardens – combined with mislabelled nursery stock - might have facilitated its country-wide distribution.”

Professor Peter Hollingsworth, Director of Science and Deputy Keeper at RBGE concluded: “The key message emerging from this study is that, while hybridisation might be frequent in locations where non-native bluebells have been introduced on a large scale, such as in the grounds of stately homes or residential areas, gene exchange does not appear to be widespread beyond the immediate contact zone.

“With lack of human intervention, hybridisation is limited in native bluebell habitats such as woodlands and rural hedgerows. Even in residential areas bordering natural bluebell populations, hybrids rarely spread out of the contact zone. Far from worrying about ‘extinction-by-hybridization’ of H. non-scripta in the UK, we should be comforted by the fact that, left to their own devices, our native bluebells have massive advantages over non-natives.”

The full research article 'Is hybridisation with non-native congeneric species a threat to the UK native bluebell Hyacinthoides non-scripta? is published in the Open Access journal 'Plants, People, Planet'.