Claytosmunda claytoniana (Interrupted Fern)

Plant Info
Also known as:
Family:Osmundaceae (Royal Fern)
Life cycle:perennial
Habitat:part shade, shade; open moist woods, swamp edges
Fruiting season:summer
Plant height:20 to 40 inches
Wetland Indicator Status:GP: FAC MW: FAC NCNE: FAC
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information


[photo of fiddlehead] As the fern emerges in the spring it is covered in a light wool but it is quickly lost.

Leaves and stems: Leaf attachment: basal Leaf type: compound

[photo of leaf] 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.

[photo of leaf underside] 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.

Spores: Fruit type: spores on stalk

[photo of developing spores] 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, formerly known as Osmunda claytoniana, 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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More photos

Photos by K. Chayka taken in Ramsey County. Photos by Peter M. Dziuk taken in Anoka and Ramsey counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Becky - East Bearskin Lake on the Gunflint Trail
on: 2017-08-02 16:50:40

Such a big, bright fern! It grows in clumps around our cabin.

Posted by: Charles L. Argue
on: 2018-06-16 12:02:08

According to 2016 Pteridophyte Phylogeny Group, now in genus Claytosmunda, a previous subgenus.

Posted by: K. Chayka
on: 2018-06-16 15:51:47

Charles, it usually takes a while before MN accepts such name changes but it will happen eventually.

Posted by: Sandra Olmsted - Ramsey Co Parkland, Vadnais Heights
on: 2020-06-07 16:54:09

The colony appeared the season after I removed all the buckthorn from a section of the park. It was the most pleasant surprise I've had out there. I've never seen this growing here before.

Posted by: Pamela Breyen - Andover
on: 2024-05-10 01:43:09

I have two large groups of interrupted fern and cinnamon. I thought they were the same for many years. The interrupted when transplanted tend to stay in the garden without moving into the lawn, the cinnamon reproduces faster and will spread faster. Some one gave me an ostrich of some kind and I can?t get rid of it. It comes up everywhere. And suggestions on how to get rid of this?

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