In addition to the true roots and aerial vine, the crown also produces underground stems called rhizomes. Rhizomes resemble roots but possess numerous buds and are used for vegetative propagation. Thus propagated, all plants of a given variety are genetically identical. Hops are dioecious, which means they have separate male and female plants. Only the female produces the flowers that are used for brewing or medicinal purposes.
Male plants have no commercial value, but are used to pollinate females.
Pollination stimulates higher yields by increasing cone size and seed set, but because brewers prefer seedless hops, males are only grown with other wise poor yielding female varieties. Hop seed from a pollinated female is only planted when a cross between the male and female is desired to obtain a new variety. Hops are native to the temperate zones of the northern hemisphere. They are found wild in western Europe, Asia and certain parts of North America. Commercial hops are generally grown between the 30th and 50th parallel north or south latitude and at various altitudes.