Japanese Hop
Humulus japonicus
Description and biology 10
- Plant: 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.
- Leaves: leaves are rough-textured, paired, simple, palmate (like a hand) with typically 5-7 lobes; leaf margins are toothed.
- Flowers, fruits and seeds: flowering occurs in July and August; male and female flowers are borne on separate plants; male flowers are very small, greenish yellow and occur in branched panicles; female flowers are in pale green, plump, drooping, cone-like structures with overlapping scales that become ‘hops’; hop scales and the seeds are covered with yellow glands; seeds are about 1/8 in. in diameter, roundish with a blunt tip, and light brown with darker specks; seeds mature through September.
- Spreads: by seed which begins to germinate in early spring, but new plants may continue to emerge as the season progresses if sunlight and moisture are available; seeds are dispersed by animals (including people), machinery and floodwaters.
- Look-alikes: native common hop (Humulus lupulus) looks very much like Japanese hop but it is usually 3-lobed or unlobed; native bur cucumber (Sicyos angulatus) lacks prickles, has tendrils, and the leaves have much less pronounced lobes.
Ecological threat in the united states 11
Japanese hop can spread to cover large areas of open ground or low vegetation including understory shrubs and small trees. 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. Japanese hop is invasive in riparian and floodplain habitats where it displaces native vegetation, prevents the emergence of new plants, and kills newly planted trees installed for streamside habitat restoration. Hop can quickly cover small trees, hiding them from view and preventing mowing or application of non-selective herbicide.
Habitat in the united states 12
Japanese hop prefers plentiful sunlight and moisture, rich exposed soil, and is most commonly found along stream banks and floodplains. Growth is less vigorous in shade and on drier soils, but it can grow in disturbed areas with fairly moist soils, including roadsides, old fields, and forest edges. In milder climates, it can survive the winter.
History in the united states 13
Japanese hop was originally imported to America in the late 1800s for use as a tonic in Asian medicine and as an ornamental vine. It is still sold for these purposes today. The common hop (Humulus lupulus) contains bitter acids and essential oils used as preservative and flavoring in beer, but the chemistry of Japanese hop is less desirable for that purpose.
Sources and Credits
- (c) Susan J. Hewitt, some rights reserved (CC BY-NC), uploaded by Susan J. Hewitt
- (c) anonymous, some rights reserved (CC BY-NC-SA), http://images.mobot.org/tropicosdetailimages/TropicosImages2/100221000/44AB5C45-4ADF-4C50-8ACE-66C84D5F9B34.jpg
- (c) anonymous, some rights reserved (CC BY-NC-SA), http://images.mobot.org/tropicosdetailimages/TropicosImages2/100221000/E3E2B1A1-7B2B-433B-AE70-AEE2C5DFCC3F.jpg
- (c) Dalgial, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/5/52/%ED%99%98%EC%82%BC%EB%8D%A9%EA%B5%B4_%EC%9E%8E.JPG
- (c) Dalgial, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/c/cb/%ED%99%98%EC%82%BC%EB%8D%A9%EA%B5%B4.JPG
- (c) anonymous, some rights reserved (CC BY-NC), http://www.illinoiswildflowers.info/weeds/photos/jp_hops1.jpg
- (c) bkmertz, some rights reserved (CC BY-NC), uploaded by bkmertz
- (c) cwwood, some rights reserved (CC BY-SA), uploaded by cwwood
- (c) awright, some rights reserved (CC BY-NC), uploaded by awright
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22734007
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22948645
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22948647
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22948648
