''Humulus japonicus'', known as Japanese hop, is an

ornamental plant Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that ...

in the family

Cannabaceae Cannabaceae is a small family of flowering plants, known as the hemp family. As now circumscribed, the family includes about 170 species grouped in about 11 genera, including ''Cannabis'' (hemp), '' Humulus'' (hops) and '' Celtis'' (hackberries ...

. Some authorities have it as a synonym of ''Humulus scandens''. Originally native to East Asian countries such as China, Japan, Korea, and extending its habitat to Vietnam, it was imported to North America in the late 19th century as an ornamental. Since its arrival in North America, it has spread widely. It can be found throughout the Northeastern U.S. and eastern Canada, and considered an invasive species in North America. It also features on the list of invasive alien species of Union Concern since 2019. This means it can no longer be imported in the European Union. Additionally, it has become illegal to plant it, breed it, transport it, or bring it into the wild in all Member States.

Nomenclature

''Humulus japonicus'' (syn. ''H. scandens'', ''Antidesma scandens'') is known by the common name of "Japanese hop", or "wild hop". The plant is called ''lü cao'' ( zh, t=葎草, labels=no) in Mandarin Chinese, and in Japanese.

Description

Well-developed leaves with 5-9 lobes; abaxial surfaces of leaves pubescent, but not densely so; infructescence rarely longer than 2 cm, with bracts and bracteoles less than 1 cm long, and notable spinulose-ciliate Inflorescences: staminate inflorescences erect, 15–25 cm, flower anthers without glands; pistillate inflorescences spikes, conelike, ovoid; bracteole ovate-orbiculate, 7–10 mm, pilose, margins densely ciliate-hairy. Infructescences pendulous, green, conelike, ovoid to oblong, (1-)1.5-3(-4) cm; bracteoles without yellow glands.

Dispersal

Seeds germinate in early spring, but plants may continue to emerge if conditions are favorable. Seeds can be dispersed by number of agents including humans, animals, machines, and flood waters.

Distribution and habitat

''Humulus japonicus'' is native temperate parts of Asia (China, Japan, Korea, Taiwan and the Russian Far East) and the tropical environment of Vietnam and Laos, but has become an invasive species in North America since it was imported in the late 19th century. The plant has been immensely successful in North America, and is found throughout eastern Canada and the eastern half of the United States, and considered a invasive species. In the United States ''Humulus japonicus'' has a lateral range from Nebraska/North Dakota to Maine and a vertical range from Minnesota to Georgia. Japanese hops grow well given plentiful sunlight, moisture, and nutrient rich soil, and are most commonly found along stream banks and floodplains. Japanese hops do not grow as well in shaded areas and drier soils. In milder climates, it can survive the winter.

Economic uses

The plant was introduced into America in the 19th century both as an ornamental and raw ingredient for the Asian tonic. In

traditional Chinese medicine Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. It has been described as "fraught with pseudoscience", with the majority of its treatments having no logical mechanism of acti ...

this herb known as ''lü cao'' is used rather uncommonly, with supposed

diuretic A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics i ...

and heat-cooling effects. Although related to the common hop ''

Humulus lupulus ''Humulus lupulus'', the common hop or hops, is a species of flowering plant in the hemp family Cannabinaceae, native to Europe, western Asia and North America. It is a perennial, herbaceous climbing plant which sends up new shoots in early s ...

'', whose cultivars are the brewer's hop used in beer production, the Japanese hop is found to be deficient in the bitter acids and

essential oils An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the o ...

used for flavoring beer, being devoid of lupulin glands (or producing very few resin glands); hence the Japanese hop is not considered viable for use in brewing.

Natural enemies

This species is a host plant for the butterfly '' Polygonia c-aureum'', the Asian comma, hence in China the butterfly is considered a major pest affecting the cash crop used in medicine.

Ecological threat

The Japanese hop can adapt well to new environments. Its range and distribution in North America prove that it can thrive in a wide range of environments, from the southern regions of the U.S. to the far reaches of northern Canada. It can grow and cover any area quickly. Thousands of hop plants can grow in one acre, and they can blanket a majority of the local vegetation. 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 whatever plants are underneath.

References

;Citations

External links

invasive.org – Japanese hop

USDA Plants Profile: ''Humulus japonicus''
{{Taxonbar, from=Q162736 japonicus Plants described in 1846