Vascular – Exotic
Dicotyledonous Herbs - Composites
Sprawling emergent perennial herb, becoming upright when flowering. Leaves are dark green, opposite, and ovate to lanceolate in shape. They vary in size from 5 to 20 cm long, 2.5 to 5 cm wide, and are on shortish stalks. Leaf margins are serrate and slightly wavy. Flowers are whitish, numerous and highly scented.
Aquatic: Emergent. The plant grows in wet marshy soils and at water margins, Plant grows in wetland communities in still or flowing water.
Perennial aquatic herb to 1+ m high. Roots finely fibrous, also aerially from stem nodes. Stems erect at first, becoming prostrate, branching and rooting at nodes, 1-1.5 m long, 5-10 mm diam at first, to 20 mm with age, hollow, inflated, floating. Leaves paired with opposite stalks joined at stem, 50-200 x 25-50 mm, lance-shaped, dark green, serrate, slightly wavy. Flowerhead clover-like, with many thin white florets, Nov-Apr. Seed yellow-brown, 5 mm diam. Plant dormant over Winter, dies back to rootstock if chilled, resprouts in Spring.
Is similar to Alternanthera philoxeroides (alligator weed) when in its sprawling phase but can be differentiated from alligator weed by its narrower leaves with serrated margins and reddish tinge. G. spilanthoides also has clusters of flowers.
December, January, February, March, April, May.
Perennial. Plants are dormant in winter, producing shoots in spring from protected buds in the nodes and crown. Reproduces sexually by seed. Vegetative reproduction occurs through the production of roots at stem nodes and vegetative fragmentation.
Seed stems and root fragments are dispersed in water, on livestock hooves and machinery. Can also be spread by dumped aquaria contents when liberating fish.
Reason for introduction
Ornamental aquarium and pond plant. Was sold in the aquarium trade as costata.
Notify regional council if found
The plant is tolerant to shade, frost and poor drainage and intolerant to drought.
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).
References and further reading
Champion et al (2012). Freshwater Pests of New Zealand. NIWA publication. http://www.niwa.co.nz/freshwater-and-estuaries/management-tools/identification-guides-and-fact-sheets/freshwater-pest-species.