Japanese Eelgrass
Nanozostera japonica
Washington State Classification
Class C — Widespread, County-Selected Control
Japanese eelgrass is non-native, difficult to control and negatively impacts the shellfish industry.
Quick Reference
Identification
Growth Habit
Japanese eelgrass is an annual to perennial, aquatic, herbaceous plant with stems growing up to around 12 inches.
Leaves
Leaves are alternately arranged and have open sheath that have 2 membranous flaps. Blades are variable in length and can be up to 13.5 inches and are very narrow (1-1.5 mm).
Flowers
Male and female flowers alternating in two rows on a thickened stem (spadix). Flowers are without petals and sepals and are small. Each male flower has a single anther and each female flower a pistil with 1 style and 2 stigmas.
Fruit & Seeds
Fruits are urticles, ellipsoid and beaked, 2.5 mm long and have one seed.
Impact
Japanese eelgrass is non-native, difficult to control and negatively impacts the shellfish industry. It was listed as a Class C noxious weed on commercially managed shellfish beds only.
Ecology & Spread
Habitat
It grows in intertidal marine waters in open tidal mudflats and sandflats, generally growing from 0.1 to 1.5m mean lower low water (MLLW). Japanese eelgrass generally grows higher in the intertidal zone than the native, common eelgrass (Zostera marina). The two species can also grow in an intermixed, mosiac pattern on mudflats with variable elevations. Please click here to see a county level distribution map of Japanese eelgrass in Washington.
Spread Mechanisms
Reproduction
It reproduces vegetatively by rhizomatous growth and it produces seeds.
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