Genetic Scorecard Indicator - Harebell/Scottish Bluebell

Moderate risk of genetic diversity loss. Diploid race 2n=34 apparently lost (Stevens et al., 2012) or more likely has never occurred (Wilson et al., 2020) in Britain. Population declines reported, especially at range edges (Braithwaite et al., 2006) and 39% in Countryside Survey (as cited in Stevens et al., 2012). These population declines may lead to further genetic diversity loss.

Population definitions:

Populations are defined based on management units. This species is widely and continuously distributed across UK in large numbers (Stroh et al., 2023; NBN, 2025). The four Great British Regions of Provenance (Herbert et al., 1999) were selected here to represent the major population groupings / management units (treating Northern Ireland as an additional region) as they broadly reflect the environmental variation across which the species is distributed and are likely to capture major patterns of genetic structure.

Ne500: The proportion of populations that have an effective population size of more than 500. 

• Proportion of populations with Ne > 500 in Scotland = 2/2
• Proportion of populations with Ne > 500 in UK = 5/5

PM: Proportion of populations that existed in 2000 that still exist in 2025.

• Proportion of populations maintained in Scotland = 2/2
• Proportion of populations maintained in UK = 5/5

Functional variation

Population declines have been reported in the north of Scotland (Stevens et al., 2012) and this may disproportionately affect the hexaploid cytotype.

Divergent lineages

Strong local structuring is apparent in distribution of tetraploids vs hexaploids: declines in north Scotland mostly impact the hexaploid populations (Stevens et al., 2012).

Hybridisation/Introgression

Tetraploids and hexaploids are usually geographically separate, but rare hybrids occur where ranges overlap with occasional aneuploids. Notable sites at which in situ polyploidisation has occurred generate occasional pentaploids. There is potential for hybridisation between in situ populations and polyploid races or non-native genotypes in seed mixes used for habitat restoration. As hybrid introgression is biased in favour of the tetraploid, hexaploid populations are particularly vulnerable to introduction of tetraploids.

Low turnover - constraints on adaptive opportunities

Late summer mowing in road verges can prevent regeneration and spread from seed.

Scotland

• Risk: Moderate
• Mitigation: Partially effective

Great Britian/UK

• Risk: Moderate
• Mitigation: Partially effective

Overall Genetic Health status explanation

Substantial populations of the species persist in a patchy distribution across the UK. Numerous projects practice grassland habitat management that should benefit the species, so genetic diversity in the wider population is likely being maintained. 

However, in many sites population decline continues. There is little evidence of awareness of the wider genetic structuring of the UK population and so local projects may not practice active management of genetic diversity, and gaps in coverage of national genetic diversity may be present.

In situ genetic threat level

• In situ Risk for Scotland: Moderate
• In situ Risk for UK: Moderate

Losses in hexaploid range, continuing threat from land use change, agricultural intensification and nitrogen pollution.

Confidence in in situ threat level

• Confidence score for Scotland: Medium
• Confidence score for UK: Medium

Assessment based on good distribution data supported by direct data on most aspects of species’ biology including cytotypes and chloroplast haplotypes but lacking a comprehensive study of genome wide genetic diversity.

Actions:

1. Nitrogen deposition control needs to continue. Measures are beginning to show results with declines in NOx over the last decade, but approximately 40% of nitrogen-sensitive habitats in Scotland exceed critical loads, and ammonia is still rising.
2. Raise awareness of polyploid spatial structure to ensure restoration projects and seed supply chains avoid inadvertent mismatch of between local and planted races.
3. Complete ex situ collections to ensure representation of, at least, both cytotypes.

Population

Demographic

N pops assessed/monitored in Scotland = 2/2
N pops assessed/monitored in UK = 5/5

Genetic

N pops assessed/monitored in Scotland = 2/2
N pops assessed/monitored in UK = 5/5

Additional work recommended to assess variation in the strength of the reproductive barriers between tetraploid and hexaploid races and whether this varies with location (i.e. at varying distances from the contact zone). Formal quantification of the extent of nuclear genetic diversity would be valuable and enable thorough evaluation of the risks posed by transplantation and hybridisation.