Sagittaria platyphylla
NPPA pest plant
Common names
Arrowhead
Biostatus
Exotic
Category
Vascular
Structural class
Herbs - Monocots
Simplified description
A marginal aquatic plant, with lance-shaped leaves, white flowers and submerged strap like leaves.
Flower colours
White
Detailed description
Emergent rhizomatous perennial herb up to c. 1 m tall. Submerged leaves are strap-shaped, 10-50 cm long and 3 cm wide with clearly visible longitudinal veins. Leaves above the water have a long petiole (c. 40 cm) which is triangular in cross section and a lance-shaped leaf blade 10-25 cm x 2-8 cm. Flowers are 3-petalled, white with 3 petals and about 6 cm across. Tubers form on rhizomes. Flowers bend downwards when fertilised (a characteristic of this species) and fruiting heads globose, 0.5-1.5 cm across, each with many seeds. Seeds are brown, wedge shaped, 2-3 mm long, 1.3 mm wide, winged with a characteristic oblique beak.
Similar taxa
Alisma spp. Alisma species have lanceolate leaves but D-shaped rather than triangular petioles and much larger inflorescenses with smaller flowers.
Distribution
Locally naturalised, mostly Auckland and Waikato Regions.
Habitat
Still and slow flowing water bodies and wetlands.
Conservation status
Not applicable
Detailed taxonomy
Family
Ecology
Flowering
November - March
Fruiting
Autumn
Year naturalised
1998
Origin
Native to North America. First recorded at a field site in New Zealand on Auckland’s North Shore in 1988.
Reason for introduction
Ornamental pond plant
Control techniques
Notify regional council if found
Life cycle and dispersal
The plant increases density and spreads locally by its creeping root system. It spreads to other areas through seed carried by water, machinery, wildlife and humans, as well as rhizome fragments being transported by ditch cleaning machinery and spoil. Spreads by water dispersed seed, rhizomes, and tubers. Also deliberate planting.
Sagittaria forms extensive infestations in shallow waterways, seriously restricting water flow and increasing sedimentation, thus aggravating flooding.
Other information
National Pest Plant Accord species
This plant is listed in the 2020 National Pest Plant Accord. The National Pest Plant Accord (NPPA) is an agreement to prevent the sale and/or distribution of specified pest plants where either formal or casual horticultural trade is the most significant way of spreading the plant in New Zealand. For up to date information and an electronic copy of the 2020 Pest Plant Accord manual (including plant information and images) visit the MPI website.
Referencing and citations
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.
Kasselmann C (2003). Aquarium plants. Krieger Publishing company, Florida, 518pp.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA). Life cycle and dispersal information from (DoC,1998).