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Book cover - Common Weeds of New ZealandAn Illustrated Guide to
Common Weeds
of New Zealand

 

Egeria densa
egeria

Family HYDROCHARITACEAE

Reproduced from
Common Weeds of New Zealand
by Ian Popay, Paul Champion & Trevor James
ISBN 0 473 09760 5
by kind permission of the
New Zealand Plant Protection Society

Publication or other use of images or descriptive text on these pages is unauthorised unless written permission is obtained from the authors and publisher.
Appropriate acknowledgement of the publication Common Weeds of New Zealand must always be given.

Available from Touchwood Books

Egeria densa - egeria

Wholly submerged, bottom-rooted, vigorous, aquatic perennial. Occurs in fresh water and can be up to 5 m tall in still water. One of the oxygen weeds, denser than Elodea and Lagarosiphon.

  • Flowers White, conspicuously protruding just above surface, up to 20 mm in diameter. Flowers have three petals 4-12 mm long and nine golden stamens. Flowers occur in the axils of the upper leaves, two to three enclosed in a spathe. Only male flowers are found in NZ.
  • Fruit Fruits not seen in NZ. Reproduction by regrowth from stem fragments.
  • Leaves Very dark green, up to 4 cm long, in whorls of four to six. Leaves abruptly narrowed to a pointed tip.
  • Stems Buoyant, slender, brittle, 3 mm in diameter. Stems up to 1 m or more long, much-branched, with nodes becoming closer together towards the stem tips.
  • Roots Bottom rooted.

Habitat

Still, shallow, enriched water in dams, ponds, drains, streams, rivers and lakes, in depths of up to 5 m.

Distribution

Abundant in Waikato hydro lakes, scattered elsewhere in NI, and occasional, but spreading in SI. Originally from South America.

Comments

Likely to spread to new waterways. Listed on the National Pest Plant Accord (see Introduction for details). The oxygen weeds include Egeria, Elodea and Lagarosiphon. In Egeria the leaves are dark green, in whorls of four or five and 12-30 mm long. The flowers are white, conspicuous and emerge above the water.

Derivation

Egeria (Lat.) = after a Roman goddess of water; densa (Lat.) = dense.

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Last updated: July 13, 2014