Japanese hops is a herbaceous annual, twining, shallow-rooted vine that can climb to heights of ten or more feet with the help of rough-textured stems covered with short, sharp, downward pointing prickles that can be very irritating to the skin. Its leaves typically have 5-7 lobes. It seems to prefer rich, moist floodplain soils and full sun. Japanese hops may be confused with the common hop(which looks like Japanese hops but is usually 3-lobed or unlobed) and native bur cucumber (which lacks prickles,has tendrils, and the leaves have much less-pronounced lobes).
How it Spreads
Japanese hops seeds are dispersed by animals, wind, and water. It appears that flowing water is the primary dispersal mechanism along rivers. Anecdotal evidence in the Blue River watershed (specifically Pleasant Valley Creek) suggests that mowing or baling equipment and bales transported for feed may be responsible for its spread between watersheds.
Impacts to Rivers
The vines grow rapidly during the summer, climbing up and over everything in their path and can form dense mats several feet deep, blocking light to plants underneath. Hop vines also twine around shrubs and trees, causing them to break or fall over. It also displaces native vegetation and prevents the emergence of new plants.
Japanese hops are noxious due to its short prickly hairs on the stems and leaves. It is unpleasant to walk through and can scrape and cut unprotected skin. Its pollen has been known as one of the important causes of hay fever and allergies in other countries where it is better established.