Acts as an annual or a perennial depending on climate. Grows up to 35′ long with downward-pointing, rough, prickly hairs on stems and leaves. Stems are light green to reddish in color and twist counterclockwise around objects.

Legal Classification in WI: Prohibited/Restricted

Leaves: Opposite, palmately lobed in 5 or more parts, 2-5″ long. Leaf stalks (petioles) are as long as or longer than the leaves. Spines at the base of each petiol point toward the soil surface.

Flowers: Midsummer to early fall lasting for about 2 months. Male and female flowers are found on separate plants (dioecious) where the leaf attaches to the stem (leaf axil). Male flowers are dull green and borne on stalks that grow upward to 10″ long and 5″ wide. Individual flowers are only 0.12″ across. Female inflourences consist of a series of overlapping bracts that can reach 1.5″ across. At the base of each bract are two inconspicuous flowers that are pale green and grow in downward-drooping clusters.

Fruits and seeds: Small (0.12” wide), dry, scale-like seeds that are easily dispersed by wind or water.

Roots: Shallow fibrous roots.

Similar species: Common hop (Humulus lupulus) leaves are 3-lobed or lack lobes. Bur cucumber (Sicyos angulatus; native) lacks prickly hairs, has tendrils, and the leaves have much less pronounced lobes. Virginia creeper (Parthenocissus quinquefolia; native) and several cinquefoil (Potentilla) species have no prickly hairs and leaves that are deeply divided into five leaflets.

Ecological threat:
• Invades flood plains, stream banks, roadsides, old fields, forest edges, and waste areas. Prefers sunny, moist areas with bare ground, but will also grow in shadier areas, especially if they are disturbed.

For more information visit: http://dnr.wi.gov/topic/Invasives/fact/JapaneseHops.html

Photo released under creative commons license.