Duck Potato or Broad-Leaved Arrowhead: A Wetland Plant in BC

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Duck potato in a creek (Photo by Linda Crampton)

Duck potato is an attractive wetland plant with large and very impressive leaves. The leaves are arrow-shaped, which gives the plant one of its common names. The mature leaves may be six to twelve inches long.  The plant grows rapidly and can be a nuisance, but it’s also interesting and even useful. I enjoy observing it.

Duck potato has the scientific name Sagittaria latifolia. The genus name is related to the word sagittate, which means arrow-shaped. The plant belongs to the family Alismataceae, which is also known as the water plantain family. It has multiple common names, including duck potato, broad-leaved arrowhead, broadleaf arrowhead, and wapato. I use all of these names interchangeably. The plant is native to North America. The word “potato” in the first common name refers to the edible tubers of the plant.

A large population of duck potatoes grows in a creek near my home. As the plant spreads, it fills the water and interferes with its flow. Every fall, the city clears the plants, since in the fall and winter the water level in the creek is often high and the water fast-moving. Next spring, the plants always reappear. They are very persistent.

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The male flowers of broad-leaved arrowhead (Photo by Linda Crampton)

The plants live in shallow and standing water. The leaves are borne on tall stems and form a rosette around the flowering stems. Submerged leaves may be narrower than the visible ones and lack the distinctive arrow shape. The male flowers have three white petals surrounding yellow stamens in the centre. The female flowers also have three petals and have green carpels in the centre. Male and female flowers may be borne on the same stems or on different ones. They are arranged around the stem in whorls of three.

The rhizomes (underground stems) of the plant are thin and white. They bear white protuberances or tubers that have a purplish tinge. These are the so-called “duck potatoes”. Ducks rarely eat them, but humans do. As always, it’s vital to identify a plant correctly when foraging for food if you decide to sample duck potatoes and to clean the tubers thoroughly.  They have to be collected from mud.

It’s said that the tubers can be eaten raw but don’t taste very nice. I’ve never eaten them myself and don’t whether the raw tubers are completely safe. When the tubers are roasted or boiled, they reportedly taste good. They have been used by indigenous people in the past and are still eaten by some people today. They are said to taste like potatoes or chestnuts when roasted.

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Himalayan balsam flowers. wapato leaves, and female wapato flowers (Photo by Linda Crampton)

In 1806, a contemporary observer named Meriwether Lewis reported that First Nations women living in the Pacific Northwest traditionally collected the tubers. They would wade in the water—sometimes up to their neck— and loosen the mud with their feet. The  tubers would then rise to the surface, enabling the women to place them in a canoe, which was used to collect the harvest. The tubers were roasted for immediate eating or pounded into a powder for future use.

Wapato is sometimes deliberately planted so that people can harvest the tubers.  Historically, the plants provided a staple crop for members of the Katzie First Nation. An interesting archaeological discovery has been made in Pitt Meadows, a city located about twenty miles from Vancouver.

A 3,800-year-old platform made of flattened stones packed together has been discovered in Pitt Meadows. Researchers say that in the past the platform was covered by water. Archaeologists have found digging tools and evidence of 4,000 wapato tubers associated with the platform. They have concluded that the platform was used as a garden for growing wapato and for preventing the tubers from developing too deep in the water to be harvested.

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Himalayan balsam flowers with wapato flowers in whorls of three (Photo by Linda Crampton)

The plants can be and have been useful. They can also be a nuisance. They are sometimes considered to be invasive. They often grow vigorously and can form masses that clog waterways and drainage ditches, potentially interfering with the flow of water. They would likely have that effect in my neighbourhood creek if the visible growth wasn’t removed every fall.

Broad-leaved arrowheads are herbaceous perennials and survive in the mud as long as their roots aren’t removed. They can also regenerate from seed, so removing their roots may not be sufficient to eliminate them. Some people don’t want to eliminate them. They are sometimes deliberately planted in water gardens for their beauty or for their tubers. They grow in USDA Plant Hardiness Zones 5 to 10.

Some people love broad-leaved arrowheads while others hate them. The plant certainly needs to be kept under control, but I enjoy seeing it regenerate in my local creek in spring. I can’t help admiring its repeated ability to overcome the stripping of plants from the creek. The large and distinctively-shaped leaves of the plant and the other plants that associate with it is an enjoyable sight.

References

  • Broad-leaved arrowhead information from E-Flora BC (a University of British Columbia website)
  • Sagittaria latifolia facts from the Missouri Botanical Garden
  • Discovery of a historical wapato garden in British Columbia from The Smithsonian Magazine
  • Information about the plant from the CABI (Centre for Agriculture and Bioscience International) Invasive Species Compendium