Tuesday, November 17, 2009

Rock Polypody

My handful of regular readers will know that I like ferns. One of our most common, in this land of rocky woods, is the common polypody (Polypodium virginianum). The polypody grows in cracks or small depressions in rocks and boulders or on cliffs, hence its other name, "rock polypody."

A walk in any woods around here eventually leads past a rock outcrop or a large boulder. These rocks host a miniature ecosystem -- much like the small terrariums we made as kids. Mosses, lichens, and ferns live separately or together under shade or part-shade.

Thoreau is said to have called these small ferns, "fresh and cheerful communities." They do brighten a woodland walk in November. Sometimes the polypody starts out on its own, in a small crack on the vertical face of a large boulder.

Its shallow roots form a mat, and are very shallow given their growing surface. The fruitdots, or sori, are round, prominent, and naked (no covering like most other ferns). Click on the photo above to see the sori on the underside of the frond.

The common polypody is evergreen, its leaves once-cut and leathery. Each leaflet is mostly entire (not lacy cut) and has a bit of a wave. The leaf, typically less than 10 inches, narrows to a blunt-tip.

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