Old World climbing fern, Lygodium microphyllum, is a large and distinctive
ground-to-crown climbing fern species. It has long climbing, stem-like fronds
(= leaves) and wiry brown rhizomes. Fronds spread along the ground, overgrow
shrubs, and also climb up and overgrow trees and other structures by twining
around them. The rhizomes can accumulate to form dense (1 m or more) mats on
the ground. The leaflets (pinnules) are of two types: non-reproductive
leaflets are unlobed along their margins, and oblong to lanceolate (pointed);
reproductive leaflets (see below) have tiny lobes along their margins covering
the sporangia (Langeland and Craddock Burks 1998).
Potentially Misidentified Species
In Florida, L. microphyllum may potentially be confused with its
congener L. japonicum, the Japanese climbing fern which is also
non-native to the state and highly invasive in habit. The
non-reproductive leaflets of L. japonicum are lobate rather than
oblong-lanceolate in form.
HABITAT AND DISTRIBUTION
L. microphyllum is believed native from Africa to Southeast Asia,
Australia, and the islands of the South Pacific (Langeland and
Craddock Burks 1998).
In Florida, Pemberton et al. (2002a) report that L. microphyllum is a
common invader in wet habitats such as bald cypress (Taxodium
distichum) stands, wet prairies, saw grass (Cladium jamaicense)
marshes, Everglades tree islands and mangrove marshes. Upland pine
flatwoods are also vulnerable to invasion as are disturbed
As of 2002, L. microphyllum was thought to be limited to
approximately the southern one-third of Florida from Highlands
County south on the Gulf coast and from Brevard County south on the
east coast (Pemberton et al. 2002a). The species is particularly
threatening to tree islands within the Everglades region where both
the density and spread of L. microphyllum are steadily increasing
(Ferriter et al. 2005).
Within the IRL watershed, L. microphyllum occurs in all counties
except Volusia County. It is substantially more abundant and
problematic in the southern half of the watershed, primarily within
Martin and Palm Beach counties (Langeland and Craddock Burks 1998). This
part of the southern IRL watershed (essentially the Loxahatchee
River basin) has been identified as the center of dispersal of Old
World climbing fern in Florida (Beckner 1968, Nauman and Austin
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
L. microphyllum is a long-lived perennial vine that can overgrow
trees to reach a height of more than 30 m (Langeland and Craddock Burks
1998, Langeland and Hutchinson 2005).
Vegetative growth and spore/gamete production reportedly occur
year-round (Langeland and Craddock Burks 1998, Pemberton et al. 2002a).
Old World climbing fern is more abundant in the southern half of
the state and the acreage occupied by this pernicious invader is
rapidly expanding. A 1993 South Florida water management District
regional survey estimated the species occupied approximately 11,000
acres in South Florida. By 1997, this number had climbed to more
than 15,000 acreas, and by 1999 the coverage was estimated at an
alarming 43,000+ acres (Pemberton and Ferriter 1998, SFWM 2004).
Old World climbing ferns employ a reproductive strategy that is
typical of ferns, alternating between vegetative and sexual
reproductive forms in successive generations. As with other ferns,
spores require a moist environment to germinate and grow
(Lott et al. 2003).
Sporangia along the margins of the reproductive leaflets produce
vegetative spores which disperse and give rise to the haploid (one
set of chromosomes) gametophyte generation of the fern. The sexual
reproductive gametophytes are small, cryptic plants similar to
liverworts. These plants are monoecious, having the reproductive
organs of both sexes present on the same plant. Male and female
swimming gametes are produced and these unite (often through
self-fertilization) to form an embryo that gives rise to the
familiar diploid sporophyte form of the fern. Production of
reproductive pinnules and sporangia occurs year-round (Langeland
and Craddock Burks 1998).
Lott et al. (2003) demonstrated that intragametophytic selfing (the
union of egg and sperm originating from the same gametophyte) is a
common reproductive strategy of both Old World climbing fern and
Japanese climbing fern in Florida. These authors and others
speculate that intragametophytic selfing has facilitated the rapid
spread of both of these invasive ferns across the state and that it
is likely the primary sexual reproductive mode at the beginning of
a new infestation. Lott et al. (2003) support this contention by
noting that the strategy is employed by other pioneering
(colonizer) ferns (e.g., Asplenium platyneuron, Onoclea
Spores typically germinate in six to seven days (Brown, 1984).
They represent the hardy dispersal stage of L. microphyllum and remain
viable for an extended period (at least two years). An 80%
germination rate has been reported for 5-month old spores, and
spores can remain viable for at least two years (Brown 1984). Spores can be transported through dispersal facilitated by
wind or water with wind being the typical mechanism of long-range
Invasive stands of L. microphyllum are capable of producing large
numbers of spores. Pemberton and Ferriter (1998) reported more
than 800 spores/cubic meter/hour were captured from a sporulating
Florida L. microphyllum infestation.
L. microphyllum is a subtropical to tropical species thus far limited in
Florida to the southern 1/3 of the peninsula although climatic analysis
indicates the northern thermal limits of the species on the east coast of
Florida may be up near the Georgia border and north of Tampa on the Gulf coast
of the state (Pemberton et al. 2002b).
Old World climbing fern is capable of growing in wet soils and even
in standing water, under light conditions ranging from shade to
full sun (Pemberton et al. 2002a). The spores require moist
conditions to germinate (Brown 1984).
L. microphyllum can be killed back by wildfire or controlled
burn, but the species is difficult to completely eliminate
(Maithana et al. 1986).
L. microphyllum tends to overgrow and dominate co-occurring vegetation (see below), reducing habitat value for associated community fauna.
A broad native range is reported for L. microphyllum, essentially extending
throughout the moist habitats of the Old World tropics (Lott et al.
2003). Much of tropical Asia, Africa, India, Australia, New Guinea,
and several Indo-Pacific nations fall within the reported native
range. Although the species is highly invasive where it has been
introduced, within its native range, it rarely if ever exhibits the
traits of an invasive species.
L. microphyllum was first found to be naturalized in Florida in
1965 (Pemberton et al. 2002a). The putative center of dispersal in Florida is within the
Loxahatchee River basin straddling Martin and Palm Beach counties.
The spread of the species across the state has been rapid, and it
can now be found on the Gulf coast north into Hillsborough County
(Pemberton and Ferriter 1998).
Old World climbing fern is listed as a Category I invasive species
(most invasive) by the Florida Exotic Plant Pest Council (Langeland
and Craddock Burks 1998).
Potential to Compete With Natives
Authors have noted that the species often becomes initially
established at the ecotone (boundary) between wetlands and drier
upland pine habitats (Langeland and Craddock Burks 1998). It can quickly
overgrow, smother, and completely dominate the native vegetation in
these habitats, resulting in reduced native biodiversity.
Moreover, it is capable of spreading into new areas in the absence
of prior habitat disturbance (Pemberton et al. 2002a).
In addition to conveying a competitive advantage, the overgrowing
and tree-climbing habit of Old World climbing ferns likely enhances long-range, wind-facilitated spore dispersal
ability of the species (Lott et al. 2003).
Once L. microphyllum has invaded and overgrown an area, it is
unlikely that native species will regain space because growing up
through the thick rhizome mats is difficult.
Because it is a ground-to-crown climbing species, Old World
climbing fern can have a significant effect as a fire carrier,
allowing fire to travel upward into the canopies of trees that
would be otherwise protected (e.g., by standing water or lack of
fuel at trunk height) from most wildfires or prescribed burns
(Roberts 1998, Pemberton et al. 2002a).
Craddock Burks (1996) indicate that some rare Florida plant species
are particularly vulnerable to L. microphyllum overgrowth,
including arboreal bromeliads such as Tillandsia utriculata which
have suffered population decline in the Loxahatchee Slough (Palm Beach
County) due to climbing fern infestation.
Possible Economic Consequences of Invasion
L. microphyllum is a non-native species that is considered an
invasive weed in Florida's natural areas. It is an aggressive
invader currently threatening many moist habitats of south and
central Florida (Pemberton and Ferriter 1998). Pemberton et al.
(2002a) refer to the species as "one of the most dangerous
weeds in southern Florida."
Limited uses have been found for L. microphyllum, including use as
a handicraft weaving material and assorted uses as an herbal
remedy, e.g., as an anti-diuretic and an anti-inflammatory agent
Chemical herbicide and mechanical control of L. microphyllum are
employed as partial remedies, but they are expensive and not
entirely effective. Such strategies can also cause unintentional
harm to native vegetation that is usually intertwined with the
Where infestations are fairly accessible (e.g., roadsides and
residential areas), herbicidal control can cost less than
$1,000/ha. Treatment of infestations in more remote settings may
be more costly, however. Bailey and Thomas (reported
in Pemberton et al. 2002a) noted that chemical treatment of L.
microphyllum infestations within Florida's Loxahatchee National
Wildlife Refuge in 2000 cost approximately $3,750/ha. These
authors noted that L. microphyllum grew back afterward and
re-treatment in 2001 was required.
Scientists from the USDA Agricultural Research Service have
investigated a couple of insects as potential biological controls
of L. microphyllum in Florida. One candidate that appears
promising at this point is a mite, Floracarus perrepae, that has
been documented to preferentially consume L. microphyllum in
Australia and Thailand (Wood 2004).
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