Arbutus unedo - EUFORGEN European forest genetic resources programme

Genetic summary

Genetic diversity and variation

The strawberry tree shows variable patterns of genetic diversity across its range. Tunisian populations display low diversity due to genetic drift, selfing, and bottlenecks linked to fragmentation and deforestation (Takrouni and Boussaid, 2010), whereas Portuguese populations retain high variability(Gomes et al., 2013). At the species level, most genetic variation occurs within rather than among populations (Takrouni and Boussaid, 2010). Overall, the species maintains high levels of variation and appears relatively insensitive to genetic erosion or isolation, as even genetically depleted populations have similar genetic diversity to healthier, more central populations (Santiso et al., 2016).

Genetic distribution and clustering

Genetic differentiation in the strawberry tree is low to moderate. Studies found low–moderate differentiation among Tunisian and Portuguese populations, attributed in part to the species’ capacity for long-distance seed dispersal (Takrouni and Boussaid, 2010). In Tunisia, differentiation levels varied regionally (Takrouni and Boussaid, 2010), while Ribeiro et al. (2017) found moderate differentiation among populations in Portugal.

Genetic clustering in the strawberry tree does not follow clear geographic or environmental patterns (Gomes et al., 2013). Tunisian populations were grouped into three clusters, suggesting differentiation occurs at a local spatial scale (Takrouni and Boussaid, 2010). In Portugal, two well-differentiated genetic clusters were identified (one in the centre of the country, one in the south), with both clusters containing populations of high genetic diversity (Ribeiro et al., 2017). Genetic diversity is significantly lower in north-western Iberia and Ireland than in populations from other areas. Populations in Ireland showed stronger genetic similarity to those in north-western Iberia than to those in nearby Atlantic France, suggesting a postglacial stepping-stone colonization along the Atlantic coast (Santiso et al., 2016).

Gene flow

Strawberry tree is a diploid species that reproduces sexually through seeds and can also spread vegetatively via root suckers (Takrouni and Boussaid, 2010). Gene flow occurs primarily through pollination by bees and other insects and seed dispersal by birds, mammals, and gravity (Takrouni and Boussaid, 2010; Gomes et al., 2013). Across the species’ range, gene flow is often restricted at small scales, with limited exchange even between trees within 500 m of each other; however, long-distance seed dispersal by frugivores, particularly birds, can occur, connecting populations over larger distances (Gomes et al., 2013). Patterns of isolation-by-distance are observed along the Atlantic coast, while Mediterranean populations maintain higher connectivity (Santiso et al., 2016).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Further relevant genetic traits

Cultivation and human intervention

Human cultivation and intervention have significantly shaped the genetic diversity and distribution of the strawberry tree. The species has long been valued for its edible fruits, medicinal uses (antiseptic, diuretic, laxative, and vascular treatments), and traditional roles such as fuelwood (Takrouni and Boussaid, 2010). Widespread and long-term human use in the Mediterranean has blurred the species’ natural geographic genetic patterns, reducing the ability to clearly distinguish between natural and human-influenced variation (Gomes et al., 2013). Despite its economic and cultural importance, breeding programmes have rarely been attempted, and most material still comes from wild populations, leading to limited selection of high-quality cultivars (Takrouni and Boussaid, 2010). However, the species is currently undergoing intense domestication in the Iberian Peninsula, especially for fruit quality traits and the production of aguardente in Portugal, where clonal propagation of selected genotypes is increasingly used (Ribeiro et al., 2017). This domestication and commercialization, including the use of clones and seed transfer from unknown origins, has the potential to alter the genetic structure of natural populations (Ribeiro et al., 2017). The species remains categorized as a neglected or underutilized crop, with growing research interest in its genetics for breeding, conservation, and industrial applications (Gomes et al., 2013).

Glacial biogeography evolution

During the Last Glacial Maximum, the strawberry tree likely survived in refugial areas in Portugal and possibly northern Africa, with most Iberian populations undergoing a postglacial expansion (Ribeiro et al., 2017). There is a clear division between Atlantic and Mediterranean lineages, suggesting the persistence of independent glacial refugia in these regions rather than more recent biogeographic barriers (Santiso et al., 2016). This historic separation explains the distinct genetic structure observed today, including the presence of the strawberry tree in Ireland but not Britain (Santiso et al., 2016). Colonization of the Atlantic coast appears to have followed a stepping-stone model, resulting in a gradual northward decline in genetic diversity, especially in Ireland (Santiso et al., 2016).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Genetic conservation

Threats

Strawberry tree faces multiple threats to its genetic resources. In North Africa, particularly Tunisia, populations are being severely reduced by deforestation, over-collecting, and their small, scattered, and declining nature (Takrouni and Boussaid, 2010). The species is increasingly threatened by climate change, habitat fragmentation, and wildfires, reducing effective population sizes and eroding genetic diversity through repeated disturbance (Ribeiro et al., 2017). Additionally, domestication practices and reliance on vegetative propagation may exacerbate risks of genetic erosion and inbreeding (Ribeiro et al., 2017). Fragmented, small populations are particularly vulnerable to genetic drift, reduced gene flow, and elevated differentiation (Takrouni and Boussaid, 2010; Gomes et al., 2013).

Management

Effective management requires both in situ and ex situ measures, with in situ protection tailored to local conditions, and ex situ collections emphasizing within-population sampling to capture local diversity (Takrouni and Boussaid, 2010). Conservation strategies should prioritize populations based on allelic richness, haplotypic uniqueness, and genetic structure (Ribeiro et al., 2017). This includes identifying key populations for conservation, such as those in Portugal as identified by Ribeiro et al., (2017). Long-term strategies should also consider the impacts of frequent wildfires, ongoing domestication, and breeding programmes, ensuring that genetic improvement efforts mirror the natural diversity and haplotypic richness of the species (Ribeiro et al., 2017).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Arbutus unedo
Strawberry tree

Environmental zones

Status of Arbutus unedo conservation in Europe

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Cultivation and human intervention

Glacial biogeography evolution

Genetic conservation

Threats

Management

Genetic Characterisation of Arbutus unedo and its GCUs

Availability of FRM

Further reading

References

Arbutus unedoStrawberry tree

Environmental zones

Status of Arbutus unedo conservation in Europe

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Cultivation and human intervention

Glacial biogeography evolution

Genetic conservation

Threats

Management

Genetic Characterisation of Arbutus unedo and its GCUs

Availability of FRM

Further reading

References

Arbutus unedo
Strawberry tree