Humulus japonicus (Japanese Hops)
|Also known as:|
|Habitat:||part shade, shade, sun; disturbed soils; roadsides, fencerows, waste places, river and stream banks, woodland edges|
|Bloom season:||July - August|
|Plant height:||3 to 20+ foot vine|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Separate male and female flowers on separate plants (dioecious). Female flowers are in short, dense, cone-like spikes about ¾ inch long at the tips of stalks arising from leaf axils and at branch tips, with a few to several flowers in a cluster. Female flowers have 2 long thread-like styles, no petals, and each surrounded by a green bract that is sparsely hairy and gland-dotted on the surface, and fringed with white hairs all around the edge.
Male flowers are in branching clusters arising from upper leaf axils and at branch tips, with 20 to 100+ flowers in a cluster. Male flowers have 5 stamens and 5 spreading sepals that are fringed with hairs. Color ranges from greenish to yellowish to pinkish-brown.
Leaves and stems:
Leaves are opposite, 1 to 6 inches long, about as wide as long, sharply toothed and finely hairy around the edges, broadly heart-shaped to nearly round in outline. Leaves are palmately lobed, most with 5 or 7 lobes, the lobes sharply pointed at the tip; some leaves may have as many as 9 lobes and occasionally those at the stem tip may have only 3. Surfaces are minutely stiff-hairy, the lower surface with scattered, long, stiff, downward pointing hairs along the veins that stick to other surfaces like Velcro™. Minute, whitish glands dot the lower surface. Leaf stalks are usually longer than the blade.
Surrounding the stalk at the leaf node are two pairs of leafy appendages (stipules) that are narrowly triangular and fringed with hairs. Stems are branched, green, and covered with a mix of short hairs and longer, stiff, downward-pointing hairs that grab onto trees and other structures and help the vine to climb. Plants can form dense monocultures, climbing surrounding vegetation and sprawling along the ground.
The story of invasive Japanese Hops in Minnesota is a sad tale. It was first recorded here in 1992 in two locations in Fillmore County, along the Root River just west of Peterson. The state's invasive species (CAPS) co-ordinator at the time attempted to round up agency and academic partners to address up-and-coming weeds, including this one, but was essentially told since the state wasn't likely to take any action they weren't interested in participating. Even the exact locations of the two known populations weren't revealed. So the hops was left to roam free and now has taken over a 40+ mile stretch of the Root River from the Mississippi River all the way to Preston. What could have been an easy eradication in 1992 has become an expensive, long-term project with much less chance of success.
Besides the Root River, Japanese Hops has also been more recently discovered in the city of Winona, along the Mississippi near the Iowa border, and on the Wisconsin side of the St. Croix River just north of Sunrise (is anyone in MN watching this one??). Expect it to continue spreading down river from those locations. Its progress is currently being tracked at EDDMapS.
Japanese Hops is very similar to the native Common Hops (Humulus lupulus), which is distinguished by nearly hairless stems (just sparse downward pointing hairs), leaf stalks mostly shorter than the blade, leaves unlobed or with 3 to 5 lobes, soft leaf hairs, and the stipules, leaves and floral bracts and sepals lacking a fringe of hairs around the edge. Japanese Hops is also an annual, where Common Hops is perennial.
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- Japanese Hops plants
- Japanese Hops plants
- an infestation of Japanese Hops
- Japanese Hops climbing over invasive Poison Hemlock
- most leaves have 5 or 7 lobes
- leaf stalk is usually longer than the blade
- fruiting branches
- close-up of late season floral bracts
- female plant coming into bloom
- male plant coming into bloom
Photos by K. Chayka taken in Fillmore and Winona counties. Photos by Peter M. Dziuk taken in Fillmore County.
Have you seen this plant in Minnesota, or have any other comments about it?