Flora of New Zealand Series

American horsebane

Procumbent or floating and ascending, aquatic biennial to perennial, with fibrous roots. Stems hollow, striate, grooved, up to 150 cm long, usually rooting at nodes. Mature stem lvs usually 2-pinnate, sometimes 3-pinnate at base, petiolate; ultimate segments ovate, lobed or not, serrate, 10-35 mm long; lvs associated with infl.-branches reduced and 1-pinnate with smaller segments; submerged lvs similar. Umbels terminal or lf-opposed, shortly pedunculate or sessile, 2-5 cm diam.; rays 10-20; rays and pedicels somewhat thickened at fruiting; bracts 0-1, linear; bracteoles numerous, linear. Fls numerous, white, c. 2 mm diam. Fr. cylindric, 2.5-3.5 mm long; ribs prominent, broad and corky; styles slender, c. = length of fr.

S.: Westland (confined to streams near Greymouth).

W. North America 1975

Aquatic of stream edges and swamps, locally well established.

FL Dec-Feb.

Poisonous (Connor 1977).