Common name: Arrowhead

Arrowhead or Swamp potato is a water plant originating from China and cultivated for its corms, which are cooked as a vegetable.

It grows partially submerged in clumps 0.5 to 1 m (1.5 to 3 ft) tall, made up of light green, erect herbaceous stems that hold large arrowhead-shaped leaves above the water. The corms are attached to the roots, which are submerged and anchor the plant firmly in the wet soil or mud.

The flowers are white, but the plant rarely flowers or sets seed. Individual clumps produce around six to ten small, onion-shaped corms with an elongated beak. They have thin light brown skin and crisp, white, starchy flesh not dissimilar to a potato.

Use

The corms are edible but must be cooked before eating. They are excellent when roasted, with a taste similar to potatoes. They are also peeled, thinly sliced and deep-fried to make a crisp, potato-chip-like snack that is especially popular during the Chinese New Year festivities. Fresh corms have a starch content of 16 to 23% and protein content of 4 to 7%.

Sagittaria species are known to tolerate and assimilates high levels of nutrients, particularly phosphorus. This makes them a good candidate for use in wastewater treatment systems, including wastewater catchments constructed to capture and treat stormwater runoff, and in wetland creation, enhancement and restoration projects.

It is also well-suited for cultivating in water gardens. However, its ability to spread vegetatively and become a weed has caused its cultivation to be discouraged outside of its natural range.

Climate

Grows well and is productive under submerged conditions in subtropical and tropical climates, generally areas with annual lows of 11 to 25°C, annual highs of 25 to 35°C and where there is permanent surface water, such as a pond or lake.

Growing

Where it is not a weed risk or prohibited from being grown, new plants are easily grown from corms, which are planted in rich soil and covered with shallow water 10 to 30 cm (4 to 12 in) deep. Good practice is to grow the plants in large containers, to help contain their spread. Corms are planted in spring, or at the start of the rainy season when air humidity levels are high.

Performs best on loose, friable, well-manured loam soils of a moderately acid to slightly alkaline nature, generally with a pH of 6.0 to 7.5, and on sites with full- to partial sun exposure. The time for harvesting is when the leaves turn yellow and die back or generally about six to seven months after sowing.

Problem features

Arrowhead is listed as a weed in the Global Invasive Species Database and other weed reference publications. It is described as a general nuisance in wetland crops, irrigation systems, drains and waterways in many countries. The seed, although rarely produced by the plant, float and are dispersed over long distances by flowing water. Plants also spread locally from vegetative material, including whole immature plants and underground corms.

Books

• Bladholm, L. 1999, The Asian grocery store demystified, 1st edition, Renaissance Books, Los Angeles, California

• Burke, D. 2005, The complete Burke's backyard : the ultimate book of fact sheets, Murdoch Books, New South Wales, Australia

• Hanson, B. 2007, Buried treasures : tasty tubers of the world : how to grown and enjoy root vegetables, tubers, rhizomes, and corms, Brooklyn Botanic Garden, Brooklyn, New York

• Herklots, G. A. C. 1972, Vegetables in south-east Asia, Allen and Unwin, London

• Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London

• Morgan, D. & Achilleos, A. 2012, Roots : the definitive compendium with more than 225 recipes, Chronicle Books, San Francisco

• Nash, H. & Slocum, P. D. & Stroupe, S. & Romar, B. 2003, Complete guide to water garden plants, Stirling Publishing, New York

• Norrington, L. & Campbell, C. 2001, Tropical food gardens : a guide to growing fruit, herbs and vegetables in tropical and sub-tropical climates, Bloomings Books, Hawthorn, Victoria

• Perkins, K. D. & Payne, W. 1981, Guide to the poisonous and irritant plants of Florida, Florida Cooperative Extension Service, Gainesville, Florida

• Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

• Rubatzky, V. E. & Yamaguchi, M. 1997, World vegetables : principles, production, and nutritive values, 2nd ed., Chapman & Hall, New York