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To learn more about the map elements, please download the "Pan-European strategy for genetic conservation of forest trees"
This distribution map has been developed by the European Commission Joint Research Centre (partly based on the EUFORGEN map) and released under Creative Commons Attribution 4.0 International (CC-BY 4.0)
Caudullo, Giovanni; Welk, Erik; San-Miguel-Ayanz, Jesús (2017). Chorological maps and data for the main European woody species. figshare. Collection. https://doi.org/10.6084/m9.figshare.c.2918528
The following experts have contributed to the development of the EUFORGEN distribution maps:
Fazia Krouchi (Algeria), Hasmik Ghalachyan (Armenia), Thomas Geburek (Austria), Berthold Heinze (Austria), Rudi Litschauer (Austria), Rudolf Litschauer (Austria), Michael Mengl (Austria), Ferdinand Müller (Austria), Franz Starlinger (Austria), Valida Ali-zade (Azerbaijan), Vahid Djalal Hajiyev (Azerbaijan), Karen Cox (Belgium), Bart De Cuyper (Belgium), Olivier Desteucq (Belgium), Patrick Mertens (Belgium), Jos Van Slycken (Belgium), An Vanden Broeck (Belgium), Kristine Vander Mijnsbrugge (Belgium), Dalibor Ballian (Bosnia and Herzegovina), Alexander H. Alexandrov (Bulgaria), Alexander Delkov (Bulgaria), Ivanova Denitsa Pandeva (Bulgaria), Peter Zhelev Stoyanov (Bulgaria), Joso Gracan (Croatia), Marilena Idzojtic (Croatia), Mladen Ivankovic (Croatia), Željka Ivanović (Croatia), Davorin Kajba (Croatia), Hrvoje Marjanovic (Croatia), Sanja Peric (Croatia), Andreas Christou (Cyprus), Xenophon Hadjikyriacou (Cyprus), Václav Buriánek (Czech Republic), Jan Chládek (Czech Republic), Josef Frýdl (Czech Republic), Petr Novotný (Czech Republic), Martin Slovacek (Czech Republic), Zdenek Špišek (Czech Republic), Karel Vancura (Czech Republic), Ulrik Bräuner (Denmark), Bjerne Ditlevsen (Denmark), Jon Kehlet Hansen (Denmark), Jan Svejgaard Jensen (Denmark), Kalev Jðgiste (Estonia), Tiit Maaten (Estonia), Raul Pihu (Estonia), Ülo Tamm (Estonia), Arvo Tullus (Estonia), Aivo Vares (Estonia), Teijo Nikkanen (Finland), Sanna Paanukoski (Finland), Mari Rusanen (Finland), Pekka Vakkari (Finland), Leena Yrjänä (Finland), Daniel Cambon (France), Eric Collin (France), Alexis Ducousso (France), Bruno Fady (France), François Lefèvre (France), Brigitte Musch (France), Sylvie Oddou-Muratorio (France), Luc E. Pâques (France), Julien Saudubray (France), Marc Villar (France), Vlatko Andonovski (FYR Macedonia), Dragi Pop-Stojanov (FYR Macedonia), Merab Machavariani (Georgia), Irina Tvauri (Georgia), Alexander Urushadze (Georgia), Bernd Degen (Germany), Jochen Kleinschmit (Germany), Armin König (Germany), Armin König (Germany), Volker Schneck (Germany), Richard Stephan (Germany), H. H. Kausch-Blecken Von Schmeling (Germany), Georg von Wühlisch (Germany), Iris Wagner (Germany), Heino Wolf (Germany), Paraskevi Alizoti (Greece), Filippos Aravanopoulos (Greece), Andreas Drouzas (Greece), Despina Paitaridou (Greece), Aristotelis C. 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Carob shows high genetic diversity within populations. Tunisian populations have high genetic variation, originating from a large ancestral gene pool before fragmentation and maintained through the species’ outcrossing system (Makrem et al., 2006). However, these same populations also showed signs of inbreeding, linked to fragmentation and restricted gene flow (Makrem et al., 2006). In Algeria, genetic surveys identified 38 unique genotypes and high levels of allelic richness, pointing to strong polymorphism within populations (Smaili et al., 2025). Moroccan populations likewise showed high levels of diversity, with 74.20% of total variation found within populations and 25.80% between populations (Zaggoumi et al., 2024).
Carob populations in the Mediterranean show moderate to high levels of genetic differentiation, with population structuring strongly influenced by geography and, to a small degree, bioclimatic conditions.
In Tunisia, populations exhibited high genetic differentiation dependent on geographic distance between populations (Makrem et al., 2006). This, combined with high genetic similarities between some populations, suggests that isolation has occurred recently, probably due to human cultivation causing habitat fragmentation (Makrem et al., 2006). Algerian populations show clustering linked to geographic distance and bioclimatic conditions, with five distinct genetic clusters identified in distinct bioclimatic zones, showing the species’ ability to adapt to different environments (Smaili et al., 2025). However, some level of gene flow was still present between populations, potentially facilitated by human-mediated seed dispersal and long-distance gene flow (Smaili et al., 2025). In Morocco, populations showed low levels of genetic differentiation across mountain ranges and different environments, but populations still showed isolation by distance, suggesting that geographic separation, combined with limited gene flow, still shaped population structure (Zaggoumi et al., 2024). In the western Mediterranean, genetic studies revealed an overall low level of diversification among populations due to the widespread asexual propagation of selected clones in cultivation (La Malfa et al., 2014).
Carob has a trioecious reproductive system (male, female, and hermaphrodite individuals), which enhances reproductive flexibility and contributes to its adaptability in diverse environments. The species is also dioecious, which enhances opportunities for cross-pollination and genetic exchange (Smaili et al., 2025). Pollination is mediated by both wind and insects, enabling gene flow within and between populations and supporting the maintenance of genetic diversity (Smaili et al., 2025).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.
Carob is valued for its resilience and as a food source, including syrup and molasses (Smaili et al., 2025). Most research on the species focuses on morphological variation in yield traits and seed characteristics, investigating ways to improve the species’ genetics for cultivation through breeding programmes (Zaggoumi et al., 2024; Smaili et al., 2025). Knowledge on the species’ genetics, especially in natural populations, will allow research and development of morphological characteristics for domestication
Cultivated populations across Italy, Malta, and Spain exhibit high admixture and broad intra-specific diversity, reflecting centuries of exchange, grafting, and selection (Caruso et al., 2008; La Malfa et al., 2014). Many cultivated accessions across Mediterranean countries share similar genetic heritage, reflecting homogenization through human activity. In contrast, wild populations show greater genetic structuring due to geographic isolation (La Malfa et al., 2014).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.
Carob populations in Tunisia have experienced significant fragmentation from human activities over the past two centuries, resulting in scattered individuals and populations (Makrem et al., 2006). This fragmentation reduces connectivity between populations, limiting gene flow and increasing the risk of genetic erosion.
In situ conservation strategies are needed and should focus on populations with a high level of genetic diversity and rare alleles. Appropriate conservation action should take account of bioclimatic zones. Ex situ preservation should be based on a maximum number of individuals collected within populations in each ecological group and their propagation in different bioclimates (Makrem et al., 2006).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.
Further reading
Barracosa, P., Lima, M.B., and Cravador, A. 2008. Analysis of genetic diversity in Portuguese Ceratonia siliqua L. cultivars using RAPD and AFLP markers. Scientia Horticulturae, 118(3): 189–199. https://doi.org/10.1016/j.scienta.2008.06.020
References
Caruso, M., La Malfa, S., Pavlíček, T., Frutos Tomñs, D., Gentile, A., and Tribulato, E. 2008. Characterisation and assessment of genetic diversity in cultivated and wild carob (Ceratonia siliqua L.) genotypes using AFLP markers. The Journal of Horticultural Science and Biotechnology, 83(2): 177–182. https://doi.org/10.1080/14620316.2008.11512367
La Malfa, S., Currò, S., Douglas, A.B., Brugaletta, M., Caruso, M., and Gentile, A. 2014. Genetic diversity revealed by EST-SSR markers in carob tree (Ceratonia siliqua L.). Biochemical Systematics and Ecology, 55: 205–211. https://doi.org/10.1016/j.bse.2014.03.022
Makrem, A., Najeh, B.F., Laarbi, K.M., and Mohamed, B. 2006. Genetic diversity in Tunisian Ceratonia siliqua L. (Caesalpinioideae) natural populations. Genetic Resources and Crop Evolution, 53(7): 1501–1511. https://doi.org/10.1007/s10722-005-7761-5
Smaili, O., Luca, L.P., Scollo, F., Chebouti-Meziou, N., Catalano, C., Di Guardo, M., Distefano, G., Nicolosi, E., Gentile, A., and La Malfa, S. 2025. Comprehensive genetic and morphological analysis of Algerian carob (Ceratonia siliqua L.) accessions. Plants, 14(7): 990. https://doi.org/10.3390/plants14070990
Zaggoumi, H., Bouda, S., Abd‑dada, H., Marghali, S., Trifi-Farah, N., and Haddioui, A. 2024. Analysis of genetic diversity of Moroccan natural carob (Ceratonia siliqua L.) populations using ISSR markers. Vegetos. https://doi.org/10.1007/s42535-024-01016-w
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