Osmunda claytoniana (Interrupted Fern)
|Also known as:|
|Family:||Osmundaceae (Royal Fern)|
|Habitat:||part shade, shade; open moist woods, swamp edges|
|Plant height:||20 to 40 inches|
|Wetland Indicator Status:||GP: FAC MW: FAC NCNE: FAC|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Leaves and stems:
Leaves are 20 to 40 inches long, once compound, generally elliptic to oblong in outline, tapering at both ends but more abruptly at the tip end; the lowest leaflets about 3 inches long. The sterile leaves grow arching in a circular clump with the fertile leaf (if present) growing more erect in the center.
Leaflets are toothless, have deep lobes, divided almost to mid-nerve, blunt at the tip and with forked lateral veins on the underside. The stem is green and slightly grooved, initially with light brown hairs but becoming smooth with age.
Bead-like capsules containing the spores attach to a stalk growing in the middle of the leaf. The capsules are initially dark green but turn dark brown with maturity. After releasing the spores, the capsules whither away leaving a large gap (i.e. “interruption”) in the middle of the leaf.
Interrupted Fern can form large colonies and has been known to hybridize with its relative Royal Fern (Osmunda regalis) but not with its relative Cinnamon Fern (formerly Osmunda cinnamomea). Since the leaves, size and overall structure of Interrupted Fern, Cinnamon Fern and Ostrich Fern (Matteuccia struthiopteris) closely resemble each other, they can most easily be distinguished by the fruiting fertile fronds—Interrupted Fern's spores are in the middle of a leaf where the other two are on separate stems. If spores are not present, the easiest way to distinguish the 3 species is to turn over the leaf and see if there is a tuft of hair at the junction of the main stem and leaflet - only Cinnamon Fern has this feature. Interrupted Fern can be distinguished from Ostrich Fern by the forked veins on the underside of the leaflets. In outline, Ostrich Fern leaves are also widest at the tip end and taper more gradually to the base, nearly to the ground, the lowest leaflets only about 1 inch long.
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Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Anoka and Ramsey counties.
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