634 Humulus lupulus L.

As this plant has been cultivated for a long time, it is often difficult to decide whether an occurrence is native or not. The species occurs in Japan as var. cordifolius (Mig.) Maxim. It is also widely distributed in N. America, partly introduced from Europe, partly native as a special taxon, viz. var. neomexicanus Nels. & Cockerell (syn.: H. americanus Nutt.). It has also been introduced into other parts of the world, e. g. to S. America and New Zealand. In many places in Eurasia too, this useful plant has escaped from cultivation and become naturalized, e. g. Ireland, Scotland, N. England and N. Scandinavia. This applies probably also to several scattered occurrences in southcentral and eastern Asia.