What does it look like?
Submerged, bottom-rooting perennial growing to 9m, with slender, brittle and branched stems (1 mm diameter). Translucent, dark green leaves (6-12 x 2 mm) in whorls of 3-8 have distinctly toothed margins, and the plant also produces small tubers and turions (hibernating buds). Only male flowers are present in New Zealand, so no seed is set.
Why is it a problem?
Grows in moderate to highly-lit submerged sites with low to high temperatures. Moderate growth rate, height, long life and density, and overtops smaller native species. Brittle stems break, and fragments and turions root downstream or wherever they are dumped. Lacks native plant competitors of similar height.