Japanese hop

(Humulus japonicus)

Conservation Status
Japanese hop
 
  IUCN Red List

not listed

     
  NatureServe

NNA - Not applicable

SNA - Not applicable

     
  Minnesota

not listed

     
           
Weed Status
   
 

SN – State prohibited noxious weed:
Eradicate List

     
           
Wetland Indicator Status
     
  Great Plains

FACU - Facultative upland

     
  Midwest

FACU - Facultative upland

     
  Northcentral & Northeast

FACU - Facultative upland

     
           
 
Description
 
 

Japanese hop is a annual vine that rises from a long taproot. It can form dense mats several feet deep covering all other vegetation.

The stem is stout, non-woody, light green, and branched. It is solid at maturity and usually finely ridged or angled. It is rough and prickly to the touch, and is densely covered with stiff, 2-branched hairs on the ridges. Each hair has two rigid branches that spread in opposite directions. These hairs facilitate climbing by anchoring the vine to adjacent plants or structures. The stem is hairiest at the nodes, and is hairless or minutely hairy between the branched hairs. It climbs by turning clockwise at the tip (twining). Charles Darwin observed that it made a complete revolution every 128 minutes during daytime in hot weather.

Leaves are opposite, broadly egg-shaped in outline, and heart-shaped at the base. They are on 1¾ to 8 long leaf stalks (petioles). The petioles are as long or longer than the leaf blades. They are sometimes twining and are sparsely to moderately covered with stiff, 2-branched hairs. At the base of each leaf is a pair of lance-shaped, leaf-like appendages (stipules). The stipules are sometimes fused, appearing as a single stipule. Leaf blades are 1¼ to 6 long, and 1½ to 7 wide. They are palmately divided into usually 5 lobes, sometimes 7 or 9 lobes. The lobes are broadly to narrowly egg-shaped, taper to a sharp point at the tip, and are somewhat narrowed at the base. The upper surface of the leaf blade is rough to the touch and is sparsely covered with stiff, prickly hairs. The lower surface is rough to the touch. It is sparsely to moderately covered with stiff, spreading, bulbous-based hairs along the veins, and is hairless but has yellow glands between the veins. The margins have sharp, forward pointing teeth and stiff, prickly, bulbous-based hairs.

Male and female flowers are borne on separate plants. The male inflorescence is loose, erect, branched cluster (panicle) of 20 to 100 or more flowers at the end of the stem and rising from leaf axils. The panicles are 6 to 10 long, and ¾ to 1½ wide. The female inflorescence is a pair of dense, cone-shaped, to ¾ long spikes (aments) drooping from leaf axils. The ament consists of overlapping, dull, pale green bracts.

Male flowers are star shaped, 1 32 to long, and about ¼ wide. There are 5 reddish sepals, no petals, and 5 stamens. The anthers are not glandular. Female flowers consist of an ovary with a long, slender stigma. They are paired between overlapping bracts of the ament.

The ament elongates when in fruit, becoming to 13 16 long. The bracts are ¼ to ½ long, egg-shaped to broadly egg-shaped, densely hairy along the margins, and sparsely to moderately hairy on the outer surface. They are not glandular. The fruit is a light brown to yellowish-brown, broadly egg-shaped to nearly spherical, to 3 16 long, 1 16 to wide seed capsule (achene) enclosed in a persistent, enlarged calyx and covered by a papery bract. It is not glandular.

 
     
 

Height

 
 

Vine: 20 to 16 or more in length

 
     
 

Flower Color

 
 

Pale green (female) and reddish (male)

 
     
 

Similar Species

 
  Common hop (Humulus lupulus) leaf blades have usually 3, occasionally 5 lobes, and sometimes no lobes on leaves near the end of the vine. The underside is hairless or softly hairy, soft to the touch. The petioles are shorter than the leaf blade. The bracts on the ament do not have hairs on the margins. The outer surface of the bracts, the anthers, and the achenes have stalked glands. The fruit structure is fragrant when crushed due to these glands.  
     
 
Habitat
 
 

Moist. Bottomland prairies, bottomland forest edges, banks of streams and rivers, roadside ditches, disturbed areas. Full sun. Rich soil.

 
     
 
Biology
 
 

Flowering

 
 

July to August

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

2, 3, 4, 7, 22, 28, 29, 30.

 
  6/2/2018      
         
 

Nativity

 
 

Native to Asia and Vietnam. Introduced and escaped cultivation. Now naturalized in North America.

 
         
 

Occurrence

 
 

Rare in Minnesota. Established in extreme southeastern counties, adventive elsewhere.

 
         
 
Taxonomy
 
  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (dicots)  
  Subclass Rosidae  
  Superorder Rosanae  
 

Order

Rosales (roses, elms, figs, and allies)  
 

Family

Cannabaceae (hemp, hop, and hackberry)  
 

Genus

Humulus (hops)  
       
 

Subordinate Taxa

 
 

 

 
       
 

Synonyms

 
 

Humulus scandens

 
       
 

Common Names

 
 

Japanese hop

 
       

 

 

 

 

 

 

 

 

 

 

 

Glossary

Achene

A dry, one-chambered, single-seeded fruit, formed from a single carpel, with the seed attached to the membranous outer layer (wall) only by the seed stalk; the wall, formed entirely from the wall of the superior ovary, does not split open at maturity, but relies on decay or predation to release the contents.

 

Ament

A cylinder-shaped, spike-like inflorescence bearing unisexual flowers that have no petals.

 

Axil

The upper angle where a branch, stem, leaf stalk, or vein diverges.

 

Bract

Modified leaf at the base of a flower stalk, flower cluster, or inflorescence.

 

Calyx

The group of outer floral leaves (sepals) below the petals, occasionally forming a tube.

 

Palmate

Similar to a hand. Having more than three lobes or leaflets that radiate from a single point at the base of the leaf.

 

Panicle

A pyramidal inflorescence with a main stem and branches. Flowers on the lower, longer branches mature earlier than those on the shorter, upper ones.

 

Petiole

The stalk of a leaf blade or compound leaf that attaches the leaf blade to the stem.

 

Sepal

An outer floral leaf, usually green but sometimes colored, at the base of a flower.

 

Stipule

A small, leaf-like, scale-like, glandular, or rarely spiny appendage found at the base of a leaf stalk, usually occurring in pairs and usually dropping soon.

 

Twining

Growing in a spiral usually around a stem of another plant that serves as support.

       
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Plant

  Japanese hop   Japanese hop
       
  Japanese hop    
       

Leaves

  Japanese hop   Japanese hop
       

Stem and Petioles

  Japanese hop    
       

Japanese hop (top) and common hop (bottom)

  Japanese hop    
       
       
       

 

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Other Videos
 
  Japanese Hop, identification of the Wisconsin Invasive Species Humulus japonicas
University of Wisconsin Extension
 
   
 
About

Published on Jul 26, 2011

This is part of a series of videos providing key characteristics for the identification of invasive plants listed in Wisconsin's invasive species administrative rule NR 40. These videos are produced by Dr. Mark Renz of the University of Wisconsin-Madison. For more information on invasive plants and invasive plant management in Wisconsin visit http://fyi.uwex.edu/weedsci

   
       
  Riparean Forests + Japanese Hop
Sarah Lancry
 
   
 
About

Published on Jun 6, 2016

This video is about the affect Japanese Hop (an invasive species) has on riparean forest's.

   
       
  BEES COLLECTING POLLEN FROM JAPANESE HOPS
Ellen McGlynn
 
   
 
About

Published on Sep 2, 2012

Bees collecting pollen from Japanese Hops (Humulus japonicus) at Big Bear Bee Farm, Clarks Summit, PA. 9/2/2012

   
       

 

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