Common Fern and Fern-Ally Species of the Northwest Forest






Terminology | Pictorial

Gymnocarpium dryopteris
Oak Fern
Polypodiaccae (Polypody Family)

Oak Fern Description

General - delicate perennial from slender, spreading, blackish rhizomes with brown, fibrous scales; stalks usually single, but often in masses, erect, 8 - 35 cm tall.

Leaves - broadly triangular in outline, 5 - 18 cm long, 5 - 25 cm wide, 2 - 3 times pinnate, hairless; 3 major, approximately equal divisions, each with 4 - 7 pairs of lobes or leaflets, smallest segments round-toothed; stalks very slender, shiny, straw-coloured, sparsely scaly at base, usually longer than blades.

Spore Clusters - small, circular dots on veins, near leaflet edges, no indusium.


Moist forests, thickets and rocky slopes; scattered across Northwestern Ontario's boreal forest north to Great Slave Lake and approximately 65 degrees N in Yukon and Alaska; circumpolar.


Also called Dryopteris disjuncta. Northern oak fern (G. Jessoense, also called G. robertianum or Dryopteris robertiana) is found on limestone and shale ledges and rock slopes across northern North America and around the world. Because of its specific habitat preferences, it is usually uncommon. Northern oak fern resembles oak fern, but its leaves are more narrowly triangular and they have dense, minute glands. The Cree used crushed oak fern leaves to repel mosquitoes and to soothe mosquito bites. These delicate little ferns can provide ground cover in shady locations. They often need soil that has been treated with lime. Oak fern is a characteristic 'indicator species' of moist sites. As moisture levels increase other species such as horsetails (Equisetum spp.) become more abundant. The genus is named Gymnocarpium, meaning 'naked fruit', because the spore clusters are not covered by an indusium.

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