Friday, January 17, 2003
When and where seen: All year round, at many places in Carlisle, and most recently in the Towle woods on January 11. Since this is an evergreen fern, it stands out nicely in fall when the forest floor is brown with dead leaves. Even now with a snow cover of 'poly' inches (enough to make more than a 'pod'), you can find the Polypody on the side of rock faces. The fronds of this clump were hanging down in parallel with icicles.
Distinguishing characteristics: The Polypody is a small fern seldom more than 10 inches tall. The leaves, or fronds, may be up to 12 inches long and are 'once-cut' into 10 to 20 pairs of simple blunt-tipped leaflets. The cut in the leaf goes almost all the way to the leaf axis. (In twice-cut ferns the leaflets are divided into sub-leaflets. The thrice-cut fern is a cut above — its sub-leaflets are cut again into leaflets.) The stalk is short and smooth. The rootstock is covered with scales, is horizontal, spreading, and often exposed.
The spore-bearing fruitdots on the underside of the leaf are large, raised, reddish brown, and appear as a single row on either side of the central vein. They are round and very prominent and may remain throughout the year. While there is no difference between the fertile and sterile fronds, lower leaflets on a frond seldom bear fruit.
Habitat: The Common Polypody likes to grow in very shallow soil. I have a clump about 3 feet in diameter in the woods in my back yard, growing in less than an inch of soil on top of a flat rock. It likes rich, woody, sub-acid soil in the shade or partial shade. It will also root and grow in tiny cracks in limestone cliffs.
Reference: Peterson Field Guides, Boughton Cobb, A Field Guide to Ferns
Ed. note: Kay Fairweather is the originator of the Biodiversity Corner. She was inspired jointly by the diversity of species in her own yard and the ease of capturing them with the digital camera. She has no formal credentials in biology or photography and would love to see contributions to the column from others similarly handicapped.
© 2003 The Carlisle Mosquito