The walnuts have always excited interest for their combination of utility and beauty, but despite this, most species of Juglans remain little known in cultivation and poorly described in the literature, while specimens in many collections are incorrectly named. This paper aims to clarify the situation with regard to the 11 hardy species and their hybrids. It should be regarded as a supplement to the information provided in the works of Elwes and Henry (1906-1913: vol. II), Bean (1973) and Krüssmann (1985).