Old World Climbing Fern

A federally listed invasive fern that climbs 100 feet into the canopy, blankets whole tree islands, and carries ground fire into the treetops. It is illegal to move or possess in Florida. This entry is for identifying and controlling it.

How to recognize it: small oblong leaflets on a wiry, endlessly twining frond that climbs into the canopy, with fringed fertile leaflets. The ID matters - the native Hartford fern is rare and protected.

You will never plant this, so what counts is telling it apart from the two other climbing ferns you might meet. All three look like a wire hung with fern leaflets; the leaflets decide it.

Old World climbing fern (L. microphyllum) has small leaflets, 1 to 2½ inches, oblong to slightly heart-shaped at the base, blunt-tipped, with smooth, unlobed edges. They are jointed where they meet the wire, so they snap off cleanly and leave a line of tiny stalk stubs behind. Fertile leaflets are the same shape but carry a fringe of small finger-like lobes along the margin, each one hooding the spore cases. In the US it is essentially a central and south Florida plant.

Japanese climbing fern (L. japonicum) has much larger, deeply cut, lacy triangular leaflets, and it is the one spread across the Gulf South and up into the Carolinas and Arkansas. It has its own entry here; it is also invasive and controlled much the same way.

American climbing fern, or Hartford fern (L. palmatum), is native, uncommon, and legally protected in several states. Its leaflets are unmistakable once you see them: hand-shaped, palmately five- to seven-lobed, like a small maple leaf on the wire. It grows on acidic, moist, sandy ground in the Appalachians and the Northeast — far outside microphyllum’s range. If you are north of Florida and the leaflets are hand-shaped, stop and leave it alone.

The habitat is the other clue. Old World climbing fern favours wet ground: cypress swamps, wet flatwoods, sawgrass edges, tree islands, marsh margins, canal and roadside ditches. It grows in full sun and in shade, which is why it invades both open marsh and closed forest, and it climbs anything — shrubs, cabbage palms, pines, cypress, fence lines.

How it spreads and why containment fails: millions of dust-fine spores ride the wind for miles and cling to gear, mulch, and vehicles, while a tough surface rhizome rebuilds every mat you cut.

This fern has no seeds and no flowers. It reproduces by spores — and it makes them in staggering numbers, on the fringed fertile leaflets, more or less year-round in south Florida. The spores are dust-fine and wind-borne, drifting for miles, which is why new infestations appear in places no one has driven, walked, or dumped. They also cling to clothing, boots, gloves, chainsaws, mowers, ATVs, and truck tires, and they travel in mulch, fill, and harvested pine straw. Every one of those is a route you can close.

Locally, the plant rebuilds from a tough, shallow, wiry rhizome at the base of the mat. Cutting the climbing fronds is the right first move and it does real good — it breaks the fire ladder and releases the smothered trees — but the rhizome resprouts, so cutting alone is never control. It also creeps outward, so a patch expands at the edges even when nothing new arrives.

The practical consequence: control has to do two separate jobs. Kill the rhizome, with repeated foliar treatment over several seasons, and stop the spores, by timing your work for still, damp conditions, bagging what you carry out, and cleaning everything that touched the plant. In heavily infested parts of Florida, land managers treat by helicopter over thousands of acres and still return on a cycle — that is the scale of the seed-free spread you are up against.

Control, not care: cut a skirt around each trunk to break the fire ladder, treat the ground mat with a labelled herbicide over several seasons, use only aquatic-labelled products at or near water, and clean every tool.

The Florida standard is the ‘hula skirt’ cut. Working around the trunk at about waist height, cut through every climbing frond so the canopy mat is severed from its roots. It browns and drops over the following weeks; the tree is released and the fire ladder is broken immediately. Then treat the ground-level mat and the regrowth. Do it in that order — spraying a canopy mat you cannot reach wastes product and drenches everything below it.

Herbicide, honestly. This fern is not controlled by cutting, and hand-pulling only works on seedlings and small new patches. In Florida the standard actives are glyphosate and metsulfuron-methyl, usually with a surfactant, applied to green foliage. Three rules are not optional. Use a product whose label lists your site — the label is the law, and a lawn-and-garden product is not licensed for a wetland edge. Read and follow that label for rate, surfactant, protective equipment, and re-entry. And because this plant lives on wet ground — swamps, ditches, canal banks, marsh margins — anything applied in, over, or near water requires an aquatic-labelled formulation, and in many situations a permit and a licensed applicator. If your infestation is at the water’s edge, call your county extension office or water management district before you buy anything.

Then keep coming back. Expect to re-treat regrowth for three to five years, and to check the site annually after that. Time your cutting for still, damp weather to limit spore release, bag anything you haul out (never compost it, never dump it), and wash tools, boots, and tires before leaving. In Florida two host-specific biocontrol agents — the Lygodium defoliating moth (Neomusotima conspurcatalis) and the Lygodium mite (Floracarus perrepae) — have been released and provide some area-wide suppression, but they will not clear your property. Finally: report it. New infestations, especially outside the known range, are worth reporting to your county extension office or state invasive-species program. Where you clear it, replant natives — swamp fern, royal fern, cinnamon fern, and native shrubs suited to your site.

The practical questions: is this it, is it the native one, why did cutting not work, why is it back, and what to do about the fire risk.

Is this Old World climbing fern? A wiry, twining, vine-like plant that is unmistakably a fern, climbing into shrubs and trees on wet ground in central or south Florida, with small oblong leaflets under about 2½ inches, smooth-edged, jointed so they snap off leaving stubs. Fertile leaflets have a fringed margin.

Could it be the native one? Yes, and this matters. Hand-shaped, palmately lobed leaflets mean the native Hartford fern (L. palmatum) — rare, protected in several states, and found in the Appalachians and Northeast, not Florida. Large, lacy, deeply cut triangular leaflets across the Gulf South mean Japanese climbing fern — also invasive, also controlled. Check the leaflet before you cut or spray anything.

I cut it down and it came back. Expected. Cutting severs the canopy mat and breaks the fire ladder, which is worth doing on its own, but the plant regrows from a surface rhizome. Cutting has to be paired with foliar treatment of the ground mat, repeated over several seasons.

It reappeared where I had cleared it. Either the rhizome survived, or spores arrived on the wind — they travel for miles, so a clean site can be re-infested from a neighbour’s property. Annual checks are part of the job.

How dangerous is the fire risk? Real and specific. The mat is continuous fuel from the ground into the crowns, so a survivable surface fire becomes a crown fire, and burning fragments lift and start spot fires downwind. Brown dry-season mats are the worst case. Break the vertical continuity with skirt cuts, keep cured mats away from structures, and talk to your county or the Florida Forest Service before burning anything on an infested site.

Can I burn it out? No. Fire does not control it, and it can move the fern and the fire into the canopy.

Is it legal to have on my property? It is a federal noxious weed and on the Florida Noxious Weed List; introducing, moving, selling, or releasing it is prohibited. Having it arrive on your land is not an offence — moving it is. Do not transport plant material, mulch, or fill off an infested site.

What should I plant instead? Native ferns and wetland plants: swamp fern, royal fern, cinnamon fern, leather fern, and native shrubs for your county. Ask a Florida native-plant nursery.

Frost is the only thing holding it back. It is at home from roughly zone 9 south - central and south Florida - and its northern edge has been creeping upward as freezes get rarer.

Old World climbing fern is a wet-tropical plant, and cold is the only real brake on it. Its US stronghold is central and south Florida, roughly zones 9 through 11, where it grows and produces spores year-round. Hard freezes brown the fronds and can kill outlying plants, which is why it has not spread across the Gulf South the way its Japanese cousin has.

Within that range it is remarkably unfussy: it grows in full sun and in deep shade, on seasonally flooded to permanently wet ground, and it climbs anything vertical. That combination lets it invade cypress domes, wet flatwoods, sawgrass marsh edges, Everglades tree islands, and canal and roadside ditches alike, and it is the reason it has become a central problem for Everglades restoration.

Its northern edge has been creeping upward as hard freezes become less frequent, and its spores are perfectly capable of arriving well north of where it can currently survive. If you garden in north Florida or the Gulf South, the useful habits are the same ones that matter in its core range: learn the leaflet, check any climbing fern you find, and report anything that looks like microphyllum outside its known range — early detection is the only cheap stage of this problem.

An ornamental curiosity in the Florida nursery trade in the late 1950s, naturalized by the mid-1960s, and by the 2000s the single largest invasive-plant problem in the Everglades - now fought with helicopters and two imported insects.

Old World climbing fern reached Florida the usual way: as an ornamental oddity, a lacy climbing fern sold and traded in the south Florida nursery world by the late 1950s. It was collected growing wild in Martin County in 1965, and for a while it looked like a minor escapee.

Then it found the wetlands. With no natural enemies, year-round growth, wind-borne spores, and a habit of climbing anything, it moved through cypress domes, wet flatwoods, and Everglades tree islands, and by the early 2000s it covered well over a hundred thousand acres of south Florida. Land managers watched it do something few invasives do: flatten the forest structure entirely, roofing tree islands in fern until the trees died and fell.

It was added to the federal noxious weed list and the Florida Noxious Weed List, and it became a line item in Everglades restoration budgets — treated by helicopter across thousands of acres, on a repeating cycle, because it always comes back. In 2008 two host-specific insects from its native range, the Lygodium defoliating moth and the Lygodium mite, were released as biological control and have established with patchy but real effect. The lesson is the ordinary one, at an extraordinary scale: a decorative import with no local enemies, sold for a few years, is still being fought sixty years later with aircraft.