Osmunda claytoniana L.
Interrupted fern
Interrupted? How can a fern be interrupted? The answer seems a little silly to me: brown fertile leaflets “interrupt” the green sterile leaflets on larger fronds. These ferns are natives of eastern Asia and North America.
Identification: Fern fronds are up to 3′ (90 cm) long and 8″ (20 cm) wide. Spore-bearing leaflets are brown, appearing in the middle of the sterile green fronds, the most obvious identifying characteristic. The leaf stalk has a round cross-section.
Habitats: Woods, hummocks in swamps.
Interrupted fern, Osmunda claytoniana, in Lac-Mégantic, Quebec, by Circeus, 7/30/2005. 
Online References:
References:
5/11/2013 · Townsend Wildlife Management Area, Townsend, Massachusetts · ≈ 7 × 9″ (17 × 23 cm) 
5/31/2010 · Mt. Lebanon St., Pepperell, Massachusetts 
5/12/2023 · Long Reach Preserve, Harpswell, Maine 
5/13/2012 · Lowell-Dracut-Tyngsboro State Forest, Lowell, Massachusetts · ≈ 1 × 1½′ (34 × 52 cm) 
5/25/2023 · Maquoit Bay Conservation Land, Brunswick, Maine 
9/13/2020 · Hidden Valley Nature Center, Jefferson, Maine · ≈ 7 × 4½″ (18 × 12 cm) 
5/11/2013 · Townsend Wildlife Management Area, Townsend, Massachusetts · ≈ 9 × 12″ (24 × 30 cm) 
5/14/2013 · Beaver Brook Conservation Area, Hollis, New Hampshire · ≈ 4½ × 7″ (12 × 18 cm) 
5/3/2025 · Merritt Mountain, Phippsburg, Maine · ≈ 4½ × 6″ (11 × 14 cm) 
5/18/2012 · Mine Falls Park, Nashua, New Hampshire · ≈ 8 × 12″ (20 × 31 cm) 
5/15/2010 · Garden in the Woods, Framingham, Massachusetts · ≈ 1½ × 1′ (52 × 34 cm) 
9/13/2020 · Hidden Valley Nature Center, Jefferson, Maine · ≈ 8 × 12″ (20 × 31 cm) 
6/9/2016 · Monhegan Island, Maine 
5/16/2024 · Ridge Trail, Freeport, Maine 
6/20/2021 · Maquoit Bay Preserve, Brunswick, Maine · ≈ 3 × 5″ (8.4 × 12 cm) 
9/20/2009 · Wild Gardens of Acadia, Acadia National Park, Bar Harbor, Maine · ≈ 15 × 10″ (39 × 26 cm) 
8/22/2020 · Crossbill Trail, Hidden Valley Nature Center, Jefferson, Maine · ≈ 6 × 10″ (16 × 24 cm) 
Once the spore-bearing fertile portions are no longer needed, they wither and disappear, leaving the “interruption.” · 6/17/2016 · Blue Trail, Willard Brook State, Ashby, Massachusetts 
5/14/2013 · Beaver Brook Conservation Area, Hollis, New Hampshire · ≈ 1½ × 2′ (47 × 57 cm) 
5/20/2023 · Knight’s Pond Preserve, Cumberland, Maine 
9/20/2009 · Wild Gardens of Acadia, Acadia National Park, Bar Harbor, Maine 
8/28/2020 · Jack’s and Litchfield Trails, Chase Reserve, Brunswick, Maine · ≈ 10 × 6″ (24 × 16 cm) 
9/20/2009 · Wild Gardens of Acadia, Acadia National Park, Bar Harbor, Maine · ≈ 1½ × 1′ (52 × 34 cm) 
5/13/2012 · Lowell-Dracut-Tyngsboro State Forest, Lowell, Massachusetts · ≈ 9 × 14″ (23 × 35 cm) 
6/20/2021 · Maquoit Bay Preserve, Brunswick, Maine · ≈ 10 × 7″ (25 × 16 cm) 
5/14/2013 · Beaver Brook Conservation Area, Hollis, New Hampshire · ≈ 6 × 9″ (16 × 23 cm) 
5/16/2024 · Ridge Trail, Freeport, Maine 
6/9/2016 · Monhegan Island, Maine 
5/15/2010 · Garden in the Woods, Framingham, Massachusetts · ≈ 2 × 1′ (62 × 41 cm) 
6/9/2016 · Monhegan Island, Maine 
6/12/2023 · Viles Arboretum, Augusta, Maine 
6/9/2016 · Monhegan Island, Maine 
5/21/2023 · Merrymeeting Fields Preserve, Woolwich, Maine 
5/13/2012 · Lowell-Dracut-Tyngsboro State Forest, Lowell, Massachusetts · ≈ 12 × 17″ (29 × 44 cm) 
5/13/2012 · Lowell-Dracut-Tyngsboro State Forest, Lowell, Massachusetts · ≈ 9 × 12″ (23 × 29 cm) 
6/9/2016 · Monhegan Island, Maine 
5/18/2021 · Cathance River Nature Preserve, Topsham, Maine · ≈ 7 × 8″ (16 × 21 cm) 
5/18/2025 · Center Point Preserve, Bowdoinham, Maine · ≈ 7 × 10″ (17 × 25 cm) 
5/17/2024 · Robert P. Tristam Coffin Wildflower Preserve, Woolwich, Maine · ≈ 5 × 8″ (13 × 20 cm) 
| Kingdom | Plantae | Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin) |
| Subkingdom | Tracheobionta | Vascular plants—plants with a “circulatory system” for delivering water and nutrients |
| Division | Pteridophyta | Ferns |
| Class | Filicopsida | “Leptosporangiate” (has to do with how their spores form) ferns—includes most ferns |
| Order | Polypodiales | Polypod ferns |
| Family | Osmundaceae | Possibly derives from Osmunder, a Saxon name for the god Thor |
| Genus | Osmunda | Possibly derives from Osmunder, a Saxon name for the god Thor |
| Species | claytoniana | For John Clayton (1694-1773), an English-born botanist in Virginia |
Osmunda claytoniana description by Thomas H. Kent, not updated.
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