T. D. Dines; R. A. Jones; S. J. Leach; D. R. McKean; D. A. Pearman; C. D. Preston; F. J. Rumsey; I. Taylor (2005). Cheffings, C. M.; Farrell, L. (eds.). "Species Status 7"(PDF). The Vascular Plant Red Data List for Great Britain. Peterborough: Joint Nature Conservation Committee: 41. ISSN1473-0154. Retrieved 11 December 2020.
T. D. Dines; R. A. Jones; S. J. Leach; D. R. McKean; D. A. Pearman; C. D. Preston; F. J. Rumsey; I. Taylor (2005). Cheffings, C. M.; Farrell, L. (eds.). "Species Status 7"(PDF). The Vascular Plant Red Data List for Great Britain. Peterborough: Joint Nature Conservation Committee: 41. ISSN1473-0154. Retrieved 11 December 2020.