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Tuberous Sword Fern


by Sharon LaPlante

Nephrolepis cordifolia is an exotic epiphytic, epilithic (on rock), or terrestrial fern in the Nephrolepidaceae or sword fern family. Other common names include: erect sword fern, tuber sword fern, fish-bone fern, ladder fern & Boston fern. Its origin is the Old World tropics.

Its leaves (fronds) can grow to three feet in length and two and a half inches wide. The petioles are up to eight inches long with brown scales. Leaflets (pinnae) can be found in numbers of 40 to 100 on each side of the main stalk (rachis). The rachis has bi-colored scales - pale brown with a distinctly darker point of attachment. The leaflets are oblong-lanceolate with a deltoid lobe at the base of each pinna and usually overlapping the stalk. Leaflets margins are entire to slightly toothed. The spores (sori) are quite abundant and are found at the end of the leaflets between the midvein and the margin with kidney-shaped tissue covering them.

Sword fern spreads by rhizomes, stolons, tubers, and spores. The tubers are globular and quite distinctive. Tuber and rhizome production increases in the presence of humus and leaf litter. This fern spreads very quickly and aggressively. This may sound like a good thing to the average gardener, but it causes havoc in natural areas. Sword fern's choice of habitat is the shade of oak hammocks and once established can take over and displace all other ground covers and low growing plants by forming impenetrable dense stands.

Florida's plants and animals depend upon functioning, biologically diverse, plant communities for food and shelter. Invasive exotic pest plants cause problems in Florida by forming monocultures. Habitat loss and alteration of plant communities has a detrimental impact on Florida's flora and fauna.

Sword fern can be confused with our native spleenwort Nephrolepis exaltata. This native does not bear the globular tubers, the main stalk has scales of only one color, and the leaflet (pinna) tips are more sharply pointed.

To learn more about invasive exotic pest plants on-line go to The Alien Plant Working Group and The Florida Exotic Pest Plant Council.


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