Nuphar polysepala aka Rocky Mountain Pond Lily

Nuphar polysepala is an aquatic perennial in the water-lily family, Nymphaeaceae. Its common names include spatterdock and Rocky Mountain pond-lily. It grows from rhizomes beneath the water. Its native range spans subarctic America and the western United States. This includes Alaska, western Canada, and parts of the southwestern states. It is not native to Britain or Ireland.

This plant grows to about 6 feet [1.8 metres]. It lives in ponds, shallow lakes, and rivers with slow currents. Wild plants grow from valleys to high mountain sites. These reach nearly 9,840 feet [3,000 metres] above sea level. Its aquatic habit makes it a plant for ponds. Flowers appear in July and August. Each flower has both male and female organs. Flies and beetles pollinate them. The seeds provide one of its recorded food uses.

Grow this species in rich soil beneath the water. It prefers sun but will also grow in light shade. Still water suits it best, though it tolerates a slow current. The suggested water depth reaches 2.5 feet [0.75 metres]. It accepts sandy, loamy, and clay soils. It also tolerates mildly acid, neutral, and mildly alkaline conditions. PFAF lists USDA hardiness zones 4–8. It reports cold tolerance near −4°F [−20°C].

Roots and seeds have recorded uses as food. Roots may be eaten raw, boiled, or baked. Dry roots can also be milled into flour. Soaking them first helps reduce their strong taste. Indigenous North Americans used the roots during food shortages. Seeds may be eaten raw or cooked. Dried seeds can be ground for porridge or bread mixtures. Roasted seeds have a flavour compared with popcorn. PFAF reports no known hazards, but this is not a full safety assessment. It also records traditional root remedies for pain and bleeding. These records do not establish medical benefit or safe use.

Propagation is possible by seed or division. Sow fresh seed in submerged pots under shallow water. Move seedlings into separate pots after their first true leaf forms. Keep them growing in greenhouse water for at least two years. Plant them out in late spring. Divide established plants in May, keeping a bud on each piece. Keep divisions in shallow water until they establish.