The Carlisle Mosquito Online

Friday, February 17, 2006


Biodiversity Corner Spinulose woodfern

This spinulose woodfern was found before last weekend's snowstorm.

Name: The spinulose woodfern, also known as the toothed woodfern, is Dryopteris spinulosa. The genus name comes from the Greek "drys" meaning oak and 'pteris' meaning fern. These ferns are usually found in oak woods. "Spinulosa'"means bearing small spines and may refer to the little scales on the stalk — but they are not exactly what I would think of as spines. There are several varieties of spinulose woodfern which are difficult to differentiate at the best of times and to make it even harder, they crossbreed readily. The spinulose woodferns as a group can be distinguished fairly easily from other Dryopteris species.

Presidents Day: A more appropriate fern for this week's topic would have been Clinton's fern, Dryopteris clintoniana, although it was not named for President Clinton. George W. Bush on the other hand has a beetle named in his honor — the slime-mold beetle, Agathidium bushi. I would like to have found any one of those, or a Lincoln's sparrow or a Jefferson salamander, but I didn't and I cannot tell a lie.

When and where seen: The spinulose woodfern is very common in woodsy wetlands. Last Saturday, before the blizzard, this evergreen fern was easy to spot against the brown of the leaf litter. There are many clumps beside the mountain bike bridge on the Tophet trail in Great Brook Farm State Park. Also, if you take the Rockstrom trail off School Street and then cross the new bridge and walk along the Poole Swamp trail you will see many clumps, some of which are sharing the habitat with another evergreen fern and close relative, the marginal woodfern or Dryopteris marginalis.

Fern language: The entire frond of a fern is considered a single leaf; the subdivisions on the frond are called leaflets. The degree of laciness of the leaflets is one of the identifying characteristics for ferns. If the leaflet is subdivided once, like the common polypody, it is called "once-cut." If the subleaflet is divided again, like the marginal woodfern, it is called "twice-cut" and if divided yet again like the spinulose woodfern it is called "thrice-cut." Ferns reproduce by spores which are formed either on specialized fertile fronds, or on the underside of the leaflets as in the spinulose woodfern. Clusters of spore cases are called sori from the Greek word meaning heaps. The location of the sori on the underside of the fern is another useful identifying characteristic.

Identification: The foliage is thrice-cut and therefore rather delicate-looking. The subleaflets have teeth which point towards the tip of the leaflet. The sori are small and located near the tips of the veins. The fronds, which are lying on the ground this time of year, are about 30 inches long. There are light brown scales on the lower part of the stalk.

Other evergreen ferns: There are two other common evergreen ferns, easy to find in any of the conservation land in Carlisle throughout the winter. They are the common polypody which is the smallest and often grows in shallow soil on rocks or in cracks in rocks, and the marginal woodfern which is comparatively leathery and has the sori positioned along the margins of the leaflets. The Christmas fern is also evergreen but much less common in Carlisle — it likes lime in the soil. It can be distinguished by the "thumbs" on the leaflets.

Clusters of spore cases are called sori and appear on the underside of the fern. Photos by Kay Fairweather

Reference: Boughton Cobb, A Field Guide to Ferns.

Submissions for the Biodiversity Corner are encouraged from everyone. You can write the column or tell me what you saw and I will write it. The only requirements are that the species exists in the wild and was seen in Carlisle. Send a note to Kay Fairweather at

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