Sagittaria platyphylla (ALISMATACEAE) Sagittaria, Arrowhead

Weeds to Whack

Sagittaria is a new weed from North America emerging in the Enoggera catchment and spreading rapidly. It has escaped from ponds, aquaria and other aquatic gardens, probably in many cases by dumping. It spreads by rhizomes, tubers, seed, tubers and entire plants which can detach and float downstream. Widespread from northern Victoria to South-East Queensland.

 Sagittaria in foreground. Photo: Robert Whyte

Foliage and Flowers

Leaves lanceolate to 25 cm, submerged translucent leaves can be 50c m with no leaf blade. The Auckland Regional Council (2002) reports, “S. platyphylla has fleshy rhizomes that are usually submerged below the water surface, while leaves are held above the surface by rigid stems. There are two kinds of leaves: emergent leaves that are linear to ovate, tapering abruptly to a point with stems that are triangular in cross-section and winged towards the base; and submerged leaves that are strap-shaped. The white or sometimes pink flowers are found in clusters of three-flowered whorls at the end of the flower stem.”

Photo: Robert Whyte

Male Flowers – Yellow Anthers

Flowers on a leafless stalk in whorls mainly in autumn. They have 3 white petals and 3 sepals. Fruit a cluster to 15 mm across, consisting of flattened, winged 1-seeded segments. reports that “The inflorescences are racemes of 3-9 whorls. Flowers can be 1.8 cm in diameter and the sepals can be spreading to recurved. Fruiting heads are 0.7-1.2 cm in diameter”.

Photo: Sheldon Navie

Female Flowers – Green Ovaries

 FNZAS classifies S. platyphylla as a swamp plant. “In Australia, S. platyphylla has become increasingly more common in irrigation supply channels, drains, shallow creeks and wetlands” (Parsons and Cuthbertson, 1992). Synonyms: Sagittaria graminea var. platyphylla Engelm, Sagittaria mohrii J.G. Sm.