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Water Shamrock (Water Clover, Pepperwort)
Marsilea quadrifolia
Water shamrock, despite its common name, is not related to shamrocks (or clover or pepper) -- it is a fern. It is native to Europe; it was introduced to America in 1862. It is considered to be potentially invasive in New England, as it may crowd out native wetland plants by forming dense stands. More on this topic from Invasive Plant Atlas of New England.
• Family: Marsileaceae
• Habitat: shallow water of lakes, ponds, or quiet sections of rivers and streams and on wet shores
• Height: leaves 1/2 inch across
• Location of spores: in hard-shelled cases borne near the roots
• Stipe (leaf stalk): green; slender and flexible
• Growth pattern: random
• Persistence: deciduous
Water shamrock is an aquatic fern.
The spores are contained in the round, brown cases. They are carried just above the roots, most often under water.