The Carlisle Mosquito Online

Friday, May 23, 2008


Interrupted Fern

The dark spore cases halfway up the fronds identify the Interrupted Fern. (Photo by Susan Emmons)

The Interrupted Fern is easily identified by the dark spore cases which appear conspicuously about halfway up the fertile fronds. Unlike many ferns which need a lot of study to determine which they are, this fern seems to shout “I am interrupted.”

The Interrupted Fern (Osmunda Claytoniana) is one of the first ferns to appear in the spring, and by mid-May it is often seen along woodsy roadsides. The name Osmunda may come from the Saxon word for the god Thor, with the Claytoniana from the 18th-century botanist, John Clayton.

This week, I saw this fern growing along Stearns Street, and also along the Tophet Trail in Great Brook Farm State Park. It is common along paths and roads in Carlisle. It grows in dry, stony areas rather than in the wetlands preferred by the similar species, the Cinnamon Fern.

This fern is a large graceful plant with coarse, curving fronds, arching out from a central point. It often reaches a height of four to five feet. The fiddleheads are covered with a wooly brown fuzz, but the green stalks become smooth, which also helps distinguish it from the Cinnamon Fern. The fertile fronds with the spore cases are similar to the sterile fronds, except that they grow more upright. The spore cases, which are on small leaflets, are green when young and turn brown with age, and by early summer have dropped off, leaving an interrupted space.

Ferns are usually described by the number of divisions on the fronds. One frond is considered the leaf, and all the subdivisions are considered leaflets. The division into leaflets is described by the “cut” – “once-cut,” “twice-cut” or even “thrice-cut,” this last one describing the laciest fronds. The Interrupted Fern is “twice-cut.” The leaf segments are rounded and deeply cut.

The Interrupted Fern occurs throughout eastern North America and also in eastern Asia. It has the oldest fossil record of any living fern. It is believed to have been in existence for 200 million years.

References. Ferns of the Northeastern United States by Farida A. Wiley, A Field Guide to Ferns by Boughton Cobb. ∆

© 2008 The Carlisle Mosquito