Nov 9, 2009

Climbing fern

Climbing fern is an unusual fern found in the higher elevations of East Tennessee. It grows like a vine, draping itself over other vegetation, but it is a fern. Ferns do not have woody stems. This plant actually produces very long fronds with leaflets every couple inches. The texture of the leaflets makes it apparent that this is a fern and not a woody plant. The stems are thin, more suggestive of tendrils than vines, and the plant has a delicate, lacy posture.

Fronds grow reproductive structures near their tips, and these have the same shape as the leaflets, but in miniature. Spore-producing organs form on the underside of these fertile leaflets.

This photograph was taken on the Obed River segment of the Cumberland Trail. American climbing fern (Lygodium palmatum) occurs throughout the Cumberland Plateau and is less common in the Smokies. Northern populations have squared-off leaflets different from the round-tipped leaflets seen here. There are also distinct coastal populations on the Atlantic and Gulf of Mexico. I wonder if anyone has studied whether we have more than one species.

There is a Japanese species of climbing fern sold as an ornamental, and an Asian species has invaded Florida, causing major problems in the Everglades. Stem-boring moths are being tested as potential biocontrols. I hope they are testing whether the moths pose a threat to native climbing ferns, though the distribution suggests they would have a difficult time spreading northward.

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