interrupted fern

(Osmunda claytoniana)

               
Conservation Status

IUCN Red List

not yet assessed

interrupted fern

NatureServe

NNR - Unranked

SNR - Unranked

Minnesota

not listed

Wetland
Indicator
Status

Great Plains

FAC - Facultative

Midwest

FAC - Facultative

Northcentral & Northeast

FAC - Facultative

Nativity

Native

Occurrence

Common

Habitat

Open, moist woods, swamp margins, shaded ledges. Full to partial shade.

Sporulation

Late April to May

     
Height

20 to 40

     

Identification

This is a large, 20 to 40 tall, erect, perennial fern that rises on a cluster of several fronds from a very large rhizome. It forms small, dense colonies.

Each plant produces one to several fertile fronds surrounded by several shorter sterile fronds.

The leaf stem (stipe) is winged and is about as long as the leaf blade. When young it is covered with orangish-brown hairs. As it ages it becomes nearly hairless.

Sterile leaf blades are elliptic to oblong in outline, 20 to 40 long, and 8 to 11¾ wide. They are pinnately divided into 15 to 25 pairs of segments (pinnae). The lowest pair of pinnae are shorter than the adjacent pair, so that the blade is widest above the base, not at the base.

The pinnae are alternate or almost opposite, spreading, oblong to lance-shaped in outline, up to 6 long, and up to 13 16 wide. They do not have a tuft of hairs at the base. They are deeply lobed (pinnatifid), with 15 to 20 lobes (pinnules) per side. The lobes are broadly oblong, squared off at the base, and rounded at the tip. The upper side is mostly hairless. The underside is slightly hairy, especially near the tip. The margins are untoothed and do not have a fringe of hairs.

Fertile leaf blades are similar to sterile ones but taller and more erect. There are 1 to 5 pairs of fertile pinnae near the middle of the blade with sterile pinnae above and below.

Fertile pinnae are medium brown to dark brown and much smaller than the sterile pinnae immediately above and below them. They are medium brown to dark brown. They are covered with numerous spore-bearing sacs (sporangia). They wither early in the season, leaving the blade with a gap in the middle, giving this plant its common name.

Spores are produced from late April to May.

 
Similar
Species

Cinnamon fern (Osmunda cinnamomea var. cinnamomea) fertile fronds are much shorter, rigidly erect, and turn cinnamon-colored when they mature. There is a tuft of brown hairs at the base of the sterile pinnae.


Distribution Distribution Map   Sources: 2, 3, 4, 5, 7, 28.

Comments

 


Taxonomy

Order:

Osmundales

 

Family:

Osmundaceae (royal fern)

 

Genus:

Osmunda

 

Section:

Claytosmunda

 
Synonyms

Osmundastrum claytonianum

 
Common
Names

interrupted fern


 

 

 

 

 

 

 

 

Glossary

frond

A large leaf with many divisions: in ferns, the compound leaf, including the stipe and the blade; in mosses, a closely and regularly branched stem resembling a fern leaf; in lichens, a stalkless, leaf-like extension.

 

pinna

The primary division of a compound leaf or fern frond.

 

pinnate

Having the leaflets of a compound leaf arranged on opposite sides of a common stalk.

 

pinnatifid

Deeply cut, more than half way to the midrib but not to the midrib, into lobes that are spaced out along the midrib; the lobes do not form separate leaflets.

 

sporangium

A spore bearing structure, as of a fern or moss.

 

stipe

A supporting stalk-like structure lacking vascular tissue: in fungi, the stalk supporting the mushroom cap; in ferns, the stalk connecting the blade to the rhizome; in flowering plants, the stalk connecting the flower’s ovary to the receptacle; in orchids; the band connecting the pollina with the viscidium.

       

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Plant

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Fertile Frond

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Sterile Frond

  interrupted fern    
       

Fertile Pinnae

  interrupted fern    
       

Sterile Pinnae

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Fall Color

  interrupted fern   interrupted fern
       
       

 

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