American Hops has some resemblance to grapevines, but it is a coarser and more bristly plant that flowers late in the year, while the latter flowers during the spring. The female fruit of hops is used to flavor beer and prevent decay during fermentation from bacterial processes. It is possible that the wind-dispersed pollen may cause allergic reactions in some people. There are both European and American varieties of this species, and it is quite possible that they have interbred in the wild. Consequently, they are often hard to distinguish. There is a variety of American Hops that has unlobed leaves. A non-native species of hops that occurs in the wild, Humulus japonicus (Japanese Hops) is a shorter vine with narrower leaves. These leaves have at most 3 lobes.