Species Spotlight: Western or Pacific oak fern (Gymnocarpium disjunctum)
This month, we cast the Species Spotlight on Western oak fern!
Pacific oak fern by Susan McDougall, Mt. Rainier Flora
Walking through Washington’s forests, it’s hard to miss Western oak fern with its distinct color brightening the understory. In the spring, its fiddleheads unfurl to reveal bright green fronds. In early fall, as they senesce or die back, these fronds fade to pale yellow or even white, adding a beautiful highlight to the autumn landscape.
Characteristics
This deciduous, perennial fern typically grows from 23 to 30 cm (8 to 16 in) tall, with broadly triangular fronds measuring 20 to 68 cm (8 to 27 in) long. The genus Gymnocarpium means “naked fruit,” referring to its spores which are not covered with an indusium or protective layer like other fern species. These are found on the underside of the fronds.
Western oak fern was recently reclassified as G. disjunctum to differentiate it from G. dyopteris, which is also referred to as Western oak fern or Northern oak fern. The two can be difficult to differentiate when young, although Gymnocarpium disjunctum tends to have slightly larger leaves.
Habitat
Despite what the name suggests, Western oak fern does not grow on or near oak trees. Rather, it prefers mid to high elevation mixed coniferous forests, relying on plenty of moisture and shade. As a result, it is often found around Douglas fir trees, Western hemlock, and Sitka spruce, along with deciduous trees such as aspen and Bigleaf maple. Gymnocarpium disjunctum also thrives around native understory such as Foamflower, Vanillaleaf, and Redwood sorrel.
Western oak fern has been documented along the West Coast of the United States stretching from Oregon to Alaska and grows on both sides of the Cascade Range.
This delicate but hardy fern is also an excellent choice for landscaping, providing lush groundcover for native plant gardens.
Conservation Status
Western oak fern is currently listed as a secure plant species in Washington. For all native plants and wildlife, our stewardship work at Nisqually Land Trust aims to establish healthy, biodiverse forests, promoting the habitat that allows these unique species to continue to thrive.