Japanese honeysuckle
Lonicera japonica Thunb.

SOURCE: The following information on this species is taken from the Plant Conservation Alliance, Alien Plant Working Group, Weeds Gone Wild website, Fact Sheets which can be found at http://www.nps.gov/plants/alien/factmain.htm and the Virginia Tech Weed Identification Guide, http://www.ppws.vt.edu/weedindex.htm. Specific species management and control information is provided elsewhere. Check the website links provided for future updates. The last update for this PCA fact sheet is March 5, 2003.

NATIVE RANGE: Japan and Korea
DESCRIPTION: Japanese honeysuckle is a perennial vine that climbs by twisting its stems around vertical structures, including limbs and trunks of shrubs and small trees. Stems become woody with maturity, are usually hairy, but sometimes not.

Photo: Chuck Bargeron, The University of Georgia, www.invasive.org.

Leaves are oblong to oval (reaching 3 inches in length and 2 inches in width), sometimes lobed, have short stalks, occur in pairs along the stem and are hairy. In southern and mid-Atlantic states, Japanese honeysuckle often remains evergreen - its leaves remain attached through the winter. In colder northern climates, the leaves may fall off after exposure to prolonged winter temperatures.

Flowers are tubular, with five fused petals, white to pink, turning yellow with age, very fragrant, and occur in pairs along the stem at leaf junctures. Stems and leaves are sometimes covered with fine, soft hairs. Japanese honeysuckle blooms from late April through July and sometimes into October. Small black fruits are produced in autumn, each containing 2-3 oval to oblong, dark brown seeds about 1/4 inch across.

Photo: Ted Bodner, Southern Weed Science Society, www.invasive.org

ECOLOGICAL THREAT: Exotic bush honeysuckles can rapidly invade and overtake a site, forming a dense shrub layer that crowds and shades out native plant species. They alter habitats by decreasing light availability, by depleting soil moisture and nutrients, and possibly by releasing toxic chemicals that prevent other plant species from growing in the vicinity. Exotic bush honeysuckles may compete with native bush honeysuckles for pollinators, resulting in reduced seed set for native species. In addition, the fruits of exotic bush honeysuckles, while abundant and rich in carbohydrates, do not offer migrating birds the high-fat, nutrient-rich food sources needed for long flights that are supplied by native plant species.

ECOLOGICAL THREAT: In North America, Japanese honeysuckle has few natural enemies which allows it to spread widely and out-compete native plant species. Its evergreen to semi-evergreen nature gives it an added advantage over native species in many areas. Shrubs and young trees can be killed by girdling when vines twist tightly around stems and trunks, cutting off the flow of water through the plant. Dense growths of honeysuckle covering vegetation can gradually kill plants by blocking sunlight from reaching their leaves. Vigorous root competition also helps Japanese honeysuckle spread and displace neighboring native vegetation.

DISTRIBUTION IN THE UNITED STATES: Japanese honeysuckle occurs across the southern U.S. from California to New England and the Great Lakes region. Escaped populations also occur in Hawaii. Severe winter temperatures and low precipitation may limit its distribution in northern latitudes and in the West, respectively. Click here to see a distribution map.

HABITAT IN THE UNITED STATES: A ubiquitous invader, Japanese honeysuckle thrives in a wide variety of habitats including fields, forests, wetlands, barrens, and all types of disturbed lands.

BACKGROUND: Japanese honeysuckle was introduced to the U.S. in the early to mid-1800's as an ornamental plant, for erosion control, and for wildlife forage and cover. Its highly fragrant flowers provide a tiny drop of honey-flavored nectar enjoyed by children.

BIOLOGY & SPREAD: Growth and spread of Japanese honeysuckle is through vegetative (plant growth) and sexual (seed) means. It produces long vegetative runners that develop roots where stem and leaf junctions (nodes) come in contact with moist soil. Underground stems (rhizomes) help to establish and spread the plant locally. Long distance dispersal is by birds and other wildlife that readily consume the fruits and defecate the seeds at various distances from the parent plant.

For more information on Japanese honeysuckle, please contact:
Ann Rhoads, University of PA, Morris Arboretum (rhoadsaf@pobox.upenn.edu)
Corey Kudrna, National Park Service, Washington, DC (corey_kudrna@nps.gov)
Element Stewardship Abstract, The Nature Conservancy http://tncweeds.ucdavis.edu/esadocs/documnts/lonijap.html
Fire Effects Information System, USDA Forest Service http://www.fs.fed.us/database/feis/plants/vine/lonjap/all.html
Identification and Biology of Non-Native Plants in Florida's Natural Areas, University of Florida http://www.fleppc.org/pdf/Lonicera%20japonica.pdf
Invasive Plant Atlas of New England, University of Connecticut http://webapps.lib.uconn.edu/ipane/browsing.cfm?descriptionid=65
Lisa Jameson, National Park Service, Washington, DC (lisa_jameson@nps.gov)
Nonnative Invasive Plants of Southern Forests - USDA Forest Service http://www.invasive.org/eastern/srs/JH.html
Plant Invaders of Mid-Atlantic Natural Areas, National Park Service and U.S. Fish and Wildlife Service http://www.invasive.org/eastern/midatlantic/loja.html
Sue Salmons, National Park Service, Rock Creek Park (sue_salmons@nps.gov)
Vikki Nuzzo, Cornell University (vnuzzo@earthlink.net)