White water crowfoot (Ranunculus aquatilis) is an interesting aquatic plant whose leaves can take two forms – threadlike, branching underwater leaves or shiny, palmately-lobed floating leaves, although not all plants have “floaters. Heterophylly (leaf shape) is influenced by interplay between environmental factors such as temperature, photo-period (length of daylight), water level, water movement, light spectrum and light intensity, among other parameters, and is reversible.
A perennial that is native to Western North America, Europe and Northwestern Africa, white water crowfoot is found in our western states, including Alaska, as well as British Columbia and the Northwest Territories in Canada. Its habitat includes ponds, streams, rivers and lakes as well as irrigation or other types of canals and ditches. Water crowfoot forms extensive mats on the surface of the water and can become a weedy nusiance. Because propagation is through seeds OR stem fragments, this aquatic can be difficult to control.
White water crowfoot stems are smooth or slightly hairy and may grow to a meter or more in length. The stems are weak, branched, root at the nodes and form dense tangles. Water crowfoot underwater leaves are alternate and branch into as many as 20 or more thread-like segments in a fan shape. When taken from the water the thread-like stems collapse into a mass. The single flowers rise on a stalks about an inch above the water surface. Five white petals blushed with yellow near the base surround a yellow center. Five sepals surround the cup-like flower. As the fruit matures the petals detach and drop. The fruit is a cluster of 10 to 50 achenes (dry seeds) with pointed ends. The seeds do not split open.
Waterfowl eat white water crowfoot seeds. There is little evidence for human culinary use. Raw the plant is poisonous and must be boiled before ingestion. While records of white water crowfoot use in India to treat fever, rheumatism and asthma exist, historically and currently white water crowfoot is not generally considered a medicinal herb.
White water crowfoot is a plant of many names. Scientifically P. aquatilis is also known as P. trychophyllus. Colloquial names include water buttercup, white water buttercup, common water crowfoot and water crowfoot.
None of the white water crowfoot plants in Ash Creek near the Dan Ryan Meadow (Lassen County CA) where these photographs were taken had “floater” leaves. Find and take pictures of white water crowfoot floating leaves is now on my “to do” list.