Monday, June 1, 2009

Landscape - Know Your Invasive Species 3: Japanese Honeysuckle

This is the third in a series on recognizing invasive species in Delaware. This post is on Japanese honeysuckle which is in flower now across Delaware.

Japanese Honeysuckle, Lonicera japonica, Honeysuckle Family (Caprifoliaceae)

Form: Woody Vine
Flowers: May–Jul
Fruits: Sep–Oct
Native Range: Japan, Korea, Eastern China

Introduction: to Long Island in 1806, spread via the nursery trade and promoted for wildlife value.

Mid-Atlantic Range & Habitats: Wood edges, old fields, ditch banks, thickets, roadsides, throughout the region.

Ecological Impacts: Japanese Honeysuckle forms dense sprawling mats that can clamber over brush and debris, excluding virtually all other vegetation, and often inhibiting forest regeneration. The vines climb high into shrubs and trees. The resulting tangles provide wildlife cover and the berries are occasionally eaten by birds and other wildlife. However, the reduction of biodiversity in invaded areas outweighs the benefits of the plant. On the Coastal Plain, where it is most abundant, ditch banks and edges that would otherwise host a diversity of native wildflowers are typically completely overtaken by this vine.

Identification: Leaves have undersides that are paler green, but not strongly whitened, sometimes hairy All leaves are opposite and distinct from each other. Flower clusters are produced in the axils of leaf pairs along the length of the stem. Fruits ripen black. When comparing to native honeysuckle species, Japanese Honeysuckle leaves are entire to sometimes lobed, whereas the leaves of the native species are always entire. The young stems of the invasive are finely hairy, while the young stems of the natives are glaucous and hairless. Japanese Honeysuckle flowers are typically white, turning to yellow. Native Trumpet Honeysuckle flowers are reddish-pink or yellow, while those of Native Twining Honeysuckle are yellow to purplish.

Japanese honeysuckle in flower. Photo by John M. Randall, The Nature Conservancy,

Japanese honeysuckle flowers and leaves. Photo by Leslie J. Mehrhoff, University of Connecticut,

Information from "Mistaken Identity - Invasive Plants and their Native Look-alikes, an Identification Guide for the Mid-Atlantic" by Matthew Sarver, Amanda Treher, Lenny Wilson, Robert Naczi, and Faith B. Kuehn. You can download the publication at:

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