Ontario Ferns website

Interrupted Fern
Osmunda claytoniana

Interrupted Fern (Osmunda claytoniana) Other common names: Clayton's Fern

Other scientific names: Osmunda interrupta

French names: Osmonde de Clayton

Family: Flowering Fern Family (Osmundaceae)

Distinctive features: Fertile leaflets are located partway up fronds.

Similar species:
  •   Cinnamon Fern (Osmundastrum cinnamomeum) - grows in wet areas; has downy stems near base; separate fertile frond; lacks the "interruption".

  •   Ostrich Fern (Matteuccia struthiopteris) - has separate fertile frond; all stems grow from a black knobby growth; lacks the "interruption".

  •   Marsh Fern (Thelypteris palustris) - crooked stem; lacks the "interruption".

Height: 1 m (2-4 ft)

Sori: Fertile leaflets partway up the frond - this is unique and distinctive.

Habitat: Forests

Native/Non-native: Native

Status: Common.

Notes: Interrupted Fern has the oldest known fossil record of any living fern in the world - it's been around for 200 million years!

Photographs: 180 photographs available, of which 15 are featured on this page. SCROLL DOWN FOR PHOTOGRAPHS.

Range Map is at the bottom of the page

Interrupted Fern (Osmunda claytoniana)

One plant growing right up against a tree.

Interrupted Fern (Osmunda claytoniana)

Another one doing the same thing.

Interrupted Fern (Osmunda claytoniana)

A nice grove of Interrupted Fern in the forest. It's a real treat to come across such a large patch of this living fossil.

The fossil record for this species goes back 200 million years, making it the oldest known fern species still living in the world!

Interrupted Fern (Osmunda claytoniana)

View from above of an Interrupted Fern. Note that all the fronds grow from one point.

Interrupted Fern (Osmunda claytoniana)

Typical frond.

Interrupted Fern (Osmunda claytoniana)

Closeup view of a frond.

Interrupted Fern (Osmunda claytoniana)

Closeup view of leaflets. Once you get to know this fern you will see that the shape of the leaflets is distinctive.

Interrupted Fern (Osmunda claytoniana)

Underside of the frond.

Interrupted Fern (Osmunda claytoniana)

Water beads up nicely on Interrupted Fern.

This photo also shows spent fertile leaflets.

Interrupted Fern (Osmunda claytoniana)

Fronds unfurling in spring (late May). Note the fertile leaflets that "interrupt" the sequence of infertile (sterile) leaflets along the stem.

Interrupted Fern (Osmunda claytoniana)

Another view of an unfurling frond in late May. Note the interruption along the stem. The dark leaflets are the fertile ones, which "interrupt" the fertile ones. No other fern in Ontario is like this. However, not all Interrupted Ferns grow fertile leaflets in a given year.

Interrupted Fern (Osmunda claytoniana)

Closeup view of young fertile leaflets.

Interrupted Fern (Osmunda claytoniana)

Spent fertile leaflets in later summer (early September).

Interrupted Fern (Osmunda claytoniana)

Herbarium specimen showing overall form.

(Royal Botanical Gardens Herbarium,Burlington,Ontario).

Interrupted Fern (Osmunda claytoniana)

In fall (early November).

Range map for Interrupted Fern (Osmunda claytoniana)

PLEASE NOTE: A coloured Province or State means this species occurs somewhere in that Province/State.
The entire Province/State is coloured, regardless of where in that Province/State it occurs.

(Range map provided courtesy of the USDA website and is displayed here in accordance with their Policies)