Sword Fern - Native or Not?

Florida’s Native and Non-Native Sword Ferns

by: Lara Miller, Natural Resource Agent

Jennifer Jones, Brooker Creek Preserve Intern

Florida is home to many native fern species, including the
Boston fern (Nephrolepis exalta) and
giant sword fern (Nephrolepis biserrata),
which can be difficult to distinguish from non-native ferns that grow in the
same environments, such as Tuberous sword fern (Nephrolepis cordifolia) and the Asian sword fern (Nephrolepis multiflora). Each of these
are often still sold in the nursery and landscape trade, and often confused or
misidentified as the native species of fern.

The Natives

The native Boston fern (Figure 1) has erect fronds that can
reach up to 3 feet long and 6 inches wide. The round sori (clusters of
spore-bearing organs) are in two rows near the underside of the pinnae
(leaflet). It is commonly found in humid forests and swamps of Florida,
although is native to other regions such as South and Central America. It is
grown outdoors as well as indoors for ornamental value; their high humidity
tolerance makes them a good candidate for both indoor and outdoor use.

Figure 1. Native
Boston Fern

The native giant sword fern (Figure 2) has fronds that extend
several feet and can be found in moist to wet soil. The species name comes from
tiny teeth that alternate with larger teeth along the edge of each lance-like
pinna. Underneath each pinna, round sori occur evenly around the entire edge. The
petioles (stalk) are sparse to moderate with reddish to light brown hair-like
scales. Tubers are never present in this
species.

Figure 2. Native
Giant Sword Fern

The Non-Natives

Since the non-native ferns can be invasive and disruptive to
native plant communities, it is very
beneficial to be able to recognize the differences between them. The Asian
sword fern and Tuberous sword fern are sold under various names, often ones of
native origin.

Tuberous sword fern (Figure 3) sometimes produces tubers, and
it is the only one of the four ferns mentioned that is capable of doing so. The presence of these tubers alone is a
distinct way to identify the species. The presence of scales on the upper
side of the rachis (stem) that is distinctively darker at the point of
attachment is another way to distinguish the tuberous sword fern from the other
three species. Native sword fern has scales on the upper side and are
homogenously colored.

Figure
3. Non-Native Tuberous Sword Fern

Tuberous sword fern can be distinguished from Asian sword
fern (Figure 4) by its glabrous central vein of the pinnae contrasted by the
presence of short stiff hairs that occur on the central vein of the pinnae of
Asian and giant sword fern. The most
distinguishing characteristic for Asian sword fern is a dense covering of dark
brown, pressed scales with pale margins on mature petioles. Petiole scales
of tuberous sword fern are dense, spreading, and pale brown, while those of
native sword fern are sparse to moderate, reddish-brown, of a single color or
slightly darkened at the point of attachment and have expanded bases with small
hairs.

Figure 4. Non-Native
Asian Sword Fern

Resources:

http://www.floridata.com/ref/n/neph_exa.cfm

http://edis.ifas.ufl.edu/uw217

http://edis.ifas.ufl.edu/pdffiles/AG/AG12000.pdf