ORIGIN

S. America

COMMON NAME

Egeria (oxygen weed)

BOTANICAL NAME

Egeria densa

IDENTIFICATION

Vigorous perennial grows submerged in up to 5m in water, forms a dense mat. Bottom rooting. Stems can be up to 5m long in still water, slender, brittle, much branched, buoyant. Soft linear leaves, dark grey-green, in whorls of 4 or 5 (sometimes 3-8), 10-30 mm long, abruptly narrowing to a sharp tip. Flowers to 20 mm across, 3 white petals, floating at water surface. Can be confused with Elodea and Lagarosiphon from which it differs by the denser, more leafy habit and 3-8 leaf whorls.

HABITATS

Near the surface in the shallow and still waters of lakes. Still enriched water of ponds, drains, streams and rivers.

IMPACT TO BIOTA AND ECOSYSTEMS

Forms dense growths displacing natives and degrading natural character of rivers and lakes. A serious threat to dune lake species, some of which are threatened plants e.g. Hydatella inconspicua.

DISPERSAL ROUTES, VECTORS, INFESTATION SOURCES

Stem fragments root easily. Brittle stems break and are transported by machinery, boat trailers etc. No seed in NZ. Also introduced into water bodies through disposal of contents of fish ponds and tanks.

MANAGEMENT

Physical Control
Cover weed mat to stop light access.

Disposal

Chemical Control
Diquat (Reglone) - see label rates. Within the Bay of Plenty region a consent is required from Environment Bay of Plenty before Diquat is applied to water.

Biological Control

Recommended Approach

FURTHER COMMENT

For further information on Egeria please refer to Environment Bay of Plenty's Fact Sheet pp1300-Aquatic Pest Plants

This plant is prohibited from propagation, sale and distribution within New Zealand!