Salix fragilis
Crack willow

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Brittle willow (Salix fragilis) is a fast-growing deciduous tree commonly found in wetland and riparian habitats. It is widely distributed across Europe and western Asia and has naturalized in many other temperate regions (Wagner, He, and Hörandl, 2021). Ecologically, it stabilizes riverbanks, provides habitat for invertebrates and birds, and resprouts readily after damage (Woodland Trust, 2026). The species is named for its brittle twigs, which break off easily and root to form new trees. Uses include basketry, bioenergy, shelterbelts, and erosion control. It thrives in moist soils, grows rapidly, and is often managed or controlled where it becomes invasive outside its native range (Woodland Trust, 2026). 

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ex situ genetic conservation unit−+
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Acknowledgements

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. Papageorgiou (Greece), Kostas Thanos (Greece), Sándor Bordács (Hungary), Csaba Mátyás (Hungary), László Nagy (Hungary), Thröstur Eysteinsson (Iceland), Adalsteinn Sigurgeirsson (Iceland), Halldór Sverrisson (Iceland), John Fennessy (Ireland), Ellen O'Connor (Ireland), Fulvio Ducci (Italy), Silvia Fineschi (Italy), Bartolomeo Schirone (Italy), Marco Cosimo Simeone (Italy), Giovanni Giuseppe Vendramin (Italy), Lorenzo Vietto (Italy), Janis Birgelis (Latvia), Virgilijus Baliuckas (Lithuania), Kestutis Cesnavicius (Lithuania), Darius Danusevicius (Lithuania), Valmantas Kundrotas (Lithuania), Alfas Pliûra (Lithuania), Darius Raudonius (Lithuania), Robert du Fays (Luxembourg), Myriam Heuertz (Luxembourg), Claude Parini (Luxembourg), Fred Trossen (Luxembourg), Frank Wolter (Luxembourg), Joseph Buhagiar (Malta), Eman Calleja (Malta), Ion Palancean (Moldova), Dragos Postolache (Moldova), Gheorghe Postolache (Moldova), Hassan Sbay (Morocco), Tor Myking (Norway), Tore Skrøppa (Norway), Anna Gugala (Poland), Jan Kowalczyk (Poland), Czeslaw Koziol (Poland), Jan Matras (Poland), Zbigniew Sobierajski (Poland), Maria Helena Almeida (Portugal), Filipe Costa e Silva (Portugal), Luís Reis (Portugal), Maria Carolina Varela (Portugal), Ioan Blada (Romania), Alexandru-Lucian Curtu (Romania), Lucian Dinca (Romania), Georgeta Mihai (Romania), Mihai Olaru (Romania), Gheorghe Parnuta (Romania), Natalia Demidova (Russian Federation), Mikhail V. Pridnya (Russian Federation), Andrey Prokazin (Russian Federation), Srdjan Bojovic (Serbia) , Vasilije Isajev (Serbia), Saša Orlovic (Serbia), Rudolf Bruchánik (Slovakia), Roman Longauer (Slovakia), Ladislav Paule (Slovakia), Gregor Bozič (Slovenia), Robert Brus (Slovenia), Katarina Celič (Slovenia), Hojka Kraigher (Slovenia), Andrej Verlič (Slovenia), Marjana Westergren (Slovenia), Ricardo Alía (Spain), Josefa Fernández-López (Spain), Luis Gil Sanchez (Spain), Pablo Gonzalez Goicoechea (Spain), Santiago C. González-Martínez (Spain), Sonia Martin Albertos (Spain), Eduardo Notivol Paino (Spain), María Arantxa Prada (Spain), Alvaro Soto de Viana (Spain), Lennart Ackzell (Sweden), Jonas Bergquist (Sweden), Sanna Black-Samuelsson (Sweden), Jonas Cedergren (Sweden), Gösta Eriksson (Sweden), Markus Bolliger (Switzerland), Felix Gugerli (Switzerland), Rolf Holderegger (Switzerland), Peter Rotach (Switzerland), Marcus Ulber (Switzerland), Sven M.G. de Vries (The Netherlands), Khouja Mohamed Larbi (Tunisia), Murat Alan (Turkey), Gaye Kandemir (Turkey), Gursel Karagöz (Turkey), Zeki Kaya (Turkey), Hasan Özer (Turkey), Hacer Semerci (Turkey), Ferit Toplu (Turkey), Mykola M. Vedmid (Ukraine), Roman T. Volosyanchuk (Ukraine), Stuart A'Hara (United Kingdom), Joan Cottrell (United Kingdom), Colin Edwards (United Kingdom), Michael Frankis (United Kingdom), Jason Hubert (United Kingdom), Karen Russell (United Kingdom), C.J.A. Samuel (United Kingdom).
 

Genetic summary

Genetic diversity and variation 

Direct, species-specific genetic studies on brittle willow are limited, and most available research focuses on its frequent hybridization with white willow (Salix alba). Broader studies on European willows indicate that species such as brittle willow show high genetic diversity within populations and low differentiation between them (Wagner, He, and Hörandl, 2021). This pattern is driven by an outcrossing breeding system, efficient wind-mediated dispersal of seed and pollen, and widespread interspecific hybridization (Wagner, He, and Hörandl, 2021). Polyploidy is also common in European willows and contributes to evolutionary flexibility (Wagner, He, and Hörandl, 2021). Most genetic variation occurs within rather than between populations, with weak geographic structure (Palmé, Semerikov, and Lascoux, 2003). 

Gene flow 

Brittle willow has high gene flow driven by wind-dispersed pollen and lightweight, tufted seeds that can travel long distances by wind and water. Its outcrossing breeding system and frequent hybridization with related willows, especially white willow, further enhance genetic mixing across populations. 


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

Further relevant genetic traits

Interspecific taxa dynamics 

Brittle willow has many interspecific interactions, especially with the closely related white willow. The two species display wide, continuous phenotypic variation, making morphological identification of pure species and hybrids difficult (Meneghetti et al., 2007). Despite this, genetic analyses show that white willow and brittle willow form two distinct genetic clusters, indicating well-differentiated gene pools (Meneghetti et al., 2007). 

Hybridization between willow species is common, with studies reporting a high frequency of hybrids in natural populations (Triest et al., 1999). Hybrids often have higher genetic variability than either parent species (Triest et al., 1999). Research shows that hybridization is widespread across the willow genus, with species such as grey willow (Salix cinerea) exchanging haplotypes and genetic material with close relatives (Palmé, Semerikov, and Lascoux, 2003). These dynamics blur species boundaries and enhance genetic variability and adaptability within natural populations (Palmé, Semerikov, and Lascoux, 2003). 
 

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

Genetic conservation

Threats 

Research on brittle willow is limited, with most genetic studies focusing on the wider willow genus or on more common species such as white willow. This makes it difficult to fully assess genetic threats specific to brittle willow, highlighting the need for further targeted research. One obvious major threat is extensive hybridization with white willow, which can erode the genetic integrity of pure brittle willow populations. Hybridization is promoted by overlapping habitats and the weakening of ecological barriers, particularly during climatic fluctuations. Future climate change may intensify this process, further threatening the preservation of distinct brittle willow gene pools (Palmé, Semerikov, and Lascoux, 2003). 

Management 

Because species-specific data is sparse, management recommendations rely on general willow genetics. Protecting genetic diversity requires identifying and conserving stands with minimal hybrid introgression. Maintaining habitat stability and reducing disturbance in riparian zones may help limit hybridization pressure. Long-term genetic monitoring is essential, and additional research focused directly on brittle willow is needed to develop effective, evidence-based conservation strategies. 
 

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

Further reading

Barcaccia, G., Meneghetti, S., Albertini, E., Triest, L., and Lucchin, M. 2003. Linkage mapping in tetraploid willows: segregation of molecular markers and estimation of linkage phases support an allotetraploid structure for Salix alba × Salix fragilis interspecific hybrids. Heredity, 90(2): 169–180. https://doi.org/10.1038/sj.hdy.6800213 

Meneghetti, S., Barcaccia, G., Paiero, P., and Lucchin, M. 2007. Genetic characterization of Salix alba L. and Salix fragilis L. by means of different PCR-derived marker systems. Plant Biosystems, 141(3): 283–291. https://doi.org/10.1080/11263500701627448 

Palmé, A.E., Semerikov, V., and Lascoux, M. 2003. Absence of geographical structure of chloroplast DNA variation in sallow, Salix caprea L. Heredity, 91(5): 465–474. https://doi.org/10.1038/sj.hdy.6800307 

Triest, L., De Greef, B., Vermeersch, S., Van Slycken, J., and Coart, E. 1999. Genetic variation and putative hybridization in Salix alba and S. fragilis (Salicaceae): evidence from allozyme data. Plant Systematics and Evolution, 215(1): 169–187. https://doi.org/10.1007/BF00984654 

Wagner, N.D., He, L., and Hörandl, E. 2021. The evolutionary history, diversity, and ecology of willows (Salix L.) in the European Alps. Diversity, 13(4): 146. https://doi.org/10.3390/d13040146 

Woodland Trust. 2026. Crack willow (Salix fragilis). Trees, woods and wildlife: A-Z of British trees. https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/crack-willow/ 

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