From WSU Extension:
As one of the most prevalent Northwest native plants, Sword Fern is best known for its bright green arching fronds that grace the shaded forest floor from the Yukon all the way south into southern California.
This evergreen groundcover fern grows to a height of 4’ with an eventual spread of 7’. Each frond is pinnately compound, and lance-shaped. The fronds are comprised of many simple, alternate leaflets or pinna(plural pinnae). These leaflets are finely serrated and have clusters of brown spore cases, called sori, on their undersides.
A mature plant can spread out to include as many as 100 dark-green leaves all originating from initial mother plant. In early spring, the young fronds, or fiddleheads, appear and begin to slowly unroll. Each frond may reach four to six feet long and will live for several years. Sword Fern does best in moist shaded conditions, but will survive well on dry sites once established as long as it has full shade. It can survive on nutrient poor sites as well, though it will not spread out as well.