10 OLD WORLD CLIMBING FERN R. W. Pemberton,1 J. A. Goolsby,2 and T. Wright3 1Invasive Plant Research Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Fort Lauderdale, Florida, USA 2Australian Biological Control Laboratory, Brisbane, Australia 3Commonwealth Science and Industrial Research Organization, Brisbane, Australia. PEST STATUS OF WEED lands near infested natural vegetation. Current con- trol costs for chemical control of L. microphyllum Old World climbing fern, Lygodium microphyllum range from $325 to $1,250/ha (D. Thayer, pers. (Cav.) R. Br. (Lygodiaceae) (Fig. 1), is an aggressive comm.). But for areas that are hard to reach, such as invasive weed of moist habitats in southern Florida the L. microphyllum infestations on the Loxahatchee (Pemberton and Ferriter, 1998). This rapidly spread- National Wildlife Refuge in Florida, the cost for a ing weed colonizes new areas without the need of single application was $3,750/ha in 2000, and since habitat disturbance and frequently completely domi- the fern has regrown the infestations were retreated nates native vegetation. Herbicidal and mechanical in 2001 (M. Bailey and W. Thomas, pers. comm.). controls are expensive, temporary solutions, and are Ecological damage. Lygodium microphyllum’s damaging to non-target plants. The fern, first found ability to grow up and over trees and shrubs and to to be naturalized in 1965, has become one of the most run horizontally allows it to smother whole commu- dangerous weeds in southern Florida. nities of plants (Figs. 2 and 3) reducing native plant diversity. It is difficult for other plants to grow through the thick fern mats (up to 1 m thick). Lygodium microphyllum is common in bald cypress (Taxodium distichum [L.] Richard) stands, but also infests pine flatwoods, wet prairies, saw grass (Cladium jamaicense Crantz) marshes, mangrove communities, Everglades tree islands, and disturbed areas. Some Everglades tree islands are so completely blanketed by the fern that it is not possible to see trees and other vegetation beneath the fern mat (Fig. 3). Lygodium microphyllum also threatens rare plants. In Loxahatchee Slough in Palm Beach County, Florida, the fern is an “imminent danger” to Tilland- sia utriculata L. and other rare bromeliads (Craddock Burks, 1996). Infestations of this fern alter the im- pact of fire, which is a naturally occurring element and a management tool in many Florida communi- Figure 1. Lygodium microphyllum showing sterile ties (Roberts, 1998). Thick skirts of old fronds en- leaflets with entire margins and fertile close trees and serve as ladders that carry fire into leaflets with sporangia-bearing teeth. (Photo tree canopies. Trees that can withstand ground fires by R. W. Pemberton.) are killed when fire is brought into the canopy. Fires that usually terminate at the margins of cypress Nature of Damage sloughs during the wet season can burn into and Economic damage. Although primarily a weed of through cypress sloughs infested with L. natural areas, L. microphyllum infests residential land- microphyllum. Portions of burning fern also can scapes, horticultural nurseries, and other managed break free and spread fire to new areas. Lygodium 139 Biological Control of Invasive Plants in the Eastern United States Dickinson State Park in Palm Beach County in 1966 (Beckner, 1968), and by 1993, it was present on 493 ha (11%) of the park and the Loxahatchee National Wild and Scenic River (Roberts, 1998). In 1995, the weed was present on 6,800 ha (12%) of the Loxahatchee National Wildlife Refuge (Palm Beach Co.), where it was undetected in 1990 (S. Jewel, pers. comm.). The land area infested by this fern is esti- mated (from aerial surveys) to have increased 150% between 1997 and 1999 (A. Ferriter, pers. comm.). Present losses due to this weed are bad, yet modest compared to potential losses unless effective controls can be found and implemented soon. Geographical Distribution In the United States. Lygodium micophyllum is a sub- tropical and tropical plant that requires shallow Figure 2. Lygodium microphyllum blanketing an aquatic habitats or moist soils. At present, L. Everglades tree island in Loxahatchee National Wildlife Refuge, Florida. (Photo by microphyllum is limited to the southern third of the Amy Ferriter, South Florida Water Florida peninsula from Brevard and Highlands Management District, West Palm Beach.) County south. The area with the lowest winter tem- peratures currently infested is Polk and Highlands Counties (ca. 28°N) in south-central Florida. These areas are in the USDA Plant Hardiness Zone 9B (minimum of 3.9 to 6.6°C) (Cathey, 1990). Because Zone 9B extends up the eastern coast to the Georgia border (ca. 30°N), the weed may well be able to colo- nize this area. Zone 9B extends to just above Tampa on the west coast of Florida. If spores of the fern are carried across the Gulf of Mexico to the southern coast of Texas and Mexico, the weed could establish in those areas because of suitable climates and habi- tats. If it establishes in Mexico, it could spread south Figure 3. Adult of Cataclysta camptozonale, an to much of wet tropical America. Lygodium Australian pyralid moth currently under microphyllum also is naturalized to a limited extent study as potential biological control agent of in Jamaica and Guyana (Pemberton and Ferriter, Lygodium microphyllum. (Photo by Christine 1998), so the opportunity for it to spread within the Bennett, Florida Biocontrol Lab, USDA, Caribbean and other tropical portions of the Ameri- ARS, Florida Division of Plant Industry, cas already exists. Gainesville.) Native range. Lygodium microphyllum has an microphyllum appears to be long-lived and persistent, exceptionally large native range, occurring in much and can occupy a large proportion of suitable habi- of the moist Old World tropics and subtropics tats in a relatively short time. The fern is classified as (Pemberton, 1998). The fern’s temperate limits are a Category I invasive species (the most invasive spe- between 28°S and 29°S in Australia and South Af- cies) by the Florida Exotic Plant Pest Council rica, and 25° N and 27°N in Assam (northeastern In- (Langeland and Craddock Burks, 1998). dia) and the Ryuku Islands (the southwestern most Extent of losses. It is hard to quantify the extent part of Japan). It spans more than half of the world’s of the losses due to Old World climbing fern. The circumference from 18°E in Senegal to 150°W in Ta- explosive growth and rapid spread of the fern are rela- hiti. In Africa, L. microphyllum ranges from Senegal tively recent. It was first collected from Jonathan south and east through most of West Africa to Zaire, 140 Old World Climbing Fern then south to Angola, east to East Africa, and then Biology south to South Africa. In Asia, the fern is distrib- uted from India and Nepal, east through much of The biology of L. microphyllum is not well studied. Southeast Asia, and north through the warmer prov- The fern is a long-lived perennial vine. The aerial inces of southern China to Taiwan and Okinawa. It vines are actually very long leaves with a stem-like also occurs throughout many of the Southeast Asian rachis and leaflet-like pinnae and pinnules compris- islands to Australia and, in the Pacific, east to Tahiti. ing the photosynthetic tissue. The plant bears both fertile leaflets with sporangia bearing teeth along the edge of the blade, and sterile leaflets with entire mar- BACKGROUND INFORMATION gins. The true stems are underground rhizomes. These vines can be 30 m in length. Growth and sporu- ON PEST PLANT lation appear to occur all year. The fern produces Taxonomy large numbers of spores; more than 800 spores/m3/ hour were trapped in one Florida infestation The correct name of Old World climbing fern is L. (Pemberton and Ferriter, 1998). Spores can germi- microphyllum (Alston and Holttum, 1959; Hanks, nate in six to seven days (Brown, 1984). Dried spores 1998), but the species is occasionally referred to as taken from the plants have germinated after two years Lygodium scandens (L.) Sw., particularly in older (Lott and Pemberton, unpub.). The life cycle of L. works. As many as 40 species have been placed in the microphyllum is the same as with other ferns. The genus Lygodium (Mabberley, 1997), but a recent re- spores require moist conditions to germinate and vision has reduced this number to 26 (Hanks, 1998). grow into small, liverwort-like gametophytes. Male All but two species are from areas with tropical or and female organs are produced on the same game- subtropical climates. The genus Lygodium has usu- tophytes and fertilization occurs when the swimming ally been placed in the Schizaeaceae, a small primi- spermatozoid swims from the male organ to a female tive family that also includes the genera Actinostachys, organ to penetrate the ovule. Fertilization gives rise Schizaea, Anemia, and Mohria (Prantl, 1881; Holttum, to the familiar large leafy fern, which is the sporo- 1973; Hanks, 1998). Since Lygodium is unique mor- phyte stage. The fern spreads locally by vegetative phologically, it is sometimes interpreted to comprise growth and over long distances by wind-borne its own monogeneric family, the Lygodiaceae spores. The plant can grow in standing water and (Bierhorst, 1971; Wagner and Smith, 1993). The re- wet soils, and either in full sun or shade. lationship of the Schizaeaceae (Lygodiaceace s.s.) to other groups of ferns is unclear (Smith, 1995). Analysis of Related Native Plants in the Eastern Lygodium microphyllum is a distinctive fern in United States North America. This vine has pinnately compound fronds (pinnules), except the sterile fronds (pinnae), In addition to L. palmatum (discussed above), there which have entire margins. Lygodium japonicum are West Indian Lygodium species that are being con- (Thunberg ex.