Nahanni Oak Fern

Appearance

At the top of the stem is a single compound leaf (frond) though appears like a whorl of 3 leaves. The leaf is generally triangular in outline, up to 15 cm long and nearly as wide, with 6 to 10 pair of branches (pinnae) oppositely arranged. The lowest pair of branches are typically twice compound, triangular in outline, to 3½ inches long, somewhat smaller than the rest of the leaf, stalked and connected to the main stem at a swollen node. Upper branches are once compound or merely lobed, stalkless, more oblong in outline but tapering to a pointed tip and generally curve upward toward the leaf tip. The leaves are held horizontally, nearly parallel to the ground, and typically bright yellow-green.

Each branch is divided into smaller segments (pinnules) that are oblong in outline but tending to curve upward toward the branch tip, divided into several rounded lobes or merely scalloped around the edges. The lowest pinnules are about as long as the second lowest. Veins are freely branched or sometimes merely forked. The upper surface is hairless, the lower surface of both leaves and stalks are sparsely to moderately glandular hairy, more densely so towards the leaf tip.

The main stem (stipe) is slender, up to about 30 cm long, dark purplish-brown at the base, greenish-brown to straw-colored above, glandular near the leaf but smooth at the base except for scattered tan scales.

The sori (group of spores) are found on the underside of the leaf. They are circular and arranged around the edges of a pinnule, at the tip of a vein, and often merge at maturity. There is no extra tissue (indusium) that surrounds or covers the spores. Spores ripen to dark brown, though not all leaves have spores.

Naming

Gymnocarpium jessoense subsp. parvulum Sarvela, Ann. Bot. Fenn. 15: 103. 1978.
Gymnocarpium jessoense (Koidzumi) Koidzumi, Acta Phytotax. Geobot. 5: 40. 1936
Dryopteris jessoensis Koidzumi, Bot. Mag. (Tokyo) 38: 104. 1924
Aspidium dryopteris (Linnaeus) Baumgarten var. longulum H. Christ
Gymnocarpium longulum (H. Christ) Kitagawa
G. robertianum (Hoffman) Newman subsp. longulum (H. Christ) Toyokuni

Distribution

Alta., B.C., Man., N.B., N.W.T., Ont., Que., Sask., Yukon; Alaska, Conn., Iowa, Maine, Mich., Minn., Vt., Wis.; Europe in Finland; Asia in Siberia, Kazakhstan.

Habitat

Acid or neutral substrates at summit of cool, shale talus slopes, and on granitic cliffs and outcrops; 0--2000 m.

Reproduction

By spores.