What Does It Look Like?
What is it?
Arrowhead (Sagittaria montevidensis) is an erect tufted aquatic annual or short-lived perennial to about 1 m tall, with 2–12 whorls of flowers at the apex. There are two kinds of leaves, emergent and submerged. The emergent leaves, which rise out of the water, are broadly arrow-shaped to 25 cm long and 20 cm wide, with long basal lobes. The submerged leaves are strap-like and translucent.
The flowers are white, sometimes with a purple patch in the centre, about 2.5 cm wide and in whorls of three, that is, three flowers arising from the same position on the stem. The lower whorls are female and the upper ones male. Both male and female flowers have 3 petals.
The fruit is a cluster about 2 cm wide with 1-seeded segments, each seed being flattened, winged and 2–3 mm long. The roots are brown and fibrous when growing as annuals but with short fleshy rhizomes (underground stems) when growing as perennials (Parsons & Cuthbertson 2001; Thorp & Wilson 1998–; Department of Agriculture and Food undated). Two subspecies of Arrowhead (Sagittaria montevidensis) have been identified in Australia. They are Sagittaria subsp. montevidensis in which the petals are white with a purple patch at the base, and Sagittaria subsp. calycina, in which the petals are white only. There are other differences in internal flower structure (see Parsons & Cuthbertson 2001).
For further information and assistance with identification of Arrowhead contact the herbarium in your state or territory.
Growth form (weed type/habit)
Where it currently grows? Preferred habitat
Arrowhead is found in shallowly flooded or marshy areas along rivers and streams. It is often cultivated in garden ponds and occurs commonly in drainage ditches, rice fields and swamps associated with irrigation systems (Parsons & Cuthbertson 2001; Thorp & Wilson 1998–).
Are there similar species?
Arrowhead may be confused with Sagittaria platyphylla, Vallisneria species, Ottelia ovalifolia and Alisma plantago-aquatica, as the submerged strap leaves of Arrowhead are similar to the juvenile leaves of these three species (Thorp & Wilson 1998–). The arrow-head shape of the emergent leaves of Arrowhead is distinctive.