Marsh Fern
Family: Thelypteridaceae
Genus: Thelypteris
Species: T. palustris
This native perennial fern has erect to ascending compound leaves about 1–2½' tall and 4-7" across. Fertile leaves tend to be a little smaller in size than infertile leaves; they are both deciduous and die down during the winter. The compound leaves are pinnate-pinnatifid in structure and lanceolate to lanceolate-oblong in outline; their petioles are pale tan or pale purplish tan and mostly glabrous. The blade tissue of these leaves is light green and hairless on both the upper and lower sides. In contrast, the central stalk (rachis) of the compound leaf and the lateral stalks (rachillae) of the pinnatifid leaflets are finely pubescent on their lower sides. Each compound leaf has 10-40 pairs of leaflets; these leaflets are deeply pinnatifid and narrowly lanceolate-oblong. Often, a compound leaf and its leaflets are slightly curved and twisted. The lobes of the leaflets are oblong or oblong-lanceolate in shape, while their margins are smooth and strongly involute (curved downward). The lobes are spaced close together along the length of each leaflet. On the lower surface of each lobe, there is a central vein with several lateral veins. Each lateral vein becomes forked and divides into two veins. On fertile leaves, round sori (spore-bearing structures) are located above the forks of each lobe. Immature sori are covered by an indusium (protective membrane) that eventually withers away. The spores are produced and released during the summer or fall. The root system is rhizomatous and fibrous. Dense colonies of compound leaves are often produced from the spreading rhizomes.
Special Adaptations:
The caterpillars of Fagitana littera (Marsh Fern Moth) feed on the leaves of this fern. The Marsh Fern is the only known host plant of this uncommon moth. Because this fern often forms dense colonies of leaves, it provides good cover for the smaller kinds of wildlife.
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