Cystopteris protrusa is a common fern of eastern North America. Throughout much of its range, it is the most common Cystopteris. It is commonly known as the lowland brittle fern or lowland fragile fern. The specific name, protrusa, refers to the fact that the rhizome protrudes a short distance beyond the current year's fronds to form the following year's leaf buds. This protrusion is a positive diagnostic in the field. Sori are round and covered in...
