National Park Mystery Plant 1: Will This “Lime-Green Cancer” Derail Everglades Restoration?

The mystery plant climbs and smothers. Photo by homeredwardprice via Wikimedia Commons.

This is the inaugural posting in our new National Park Mystery Plant series. We hope to eventually make the mystery plant quiz a regular feature of Traveler.

This virulently invasive plant, sometimes called the “lime-green cancer,” is arguably the most dangerous plant in Florida. It already infests Everglades National Park, and if it isn’t controlled it might obliterate decades of ecosystem restoration efforts. Do you know what this nightmare plant is?

It’s native to wet or moist subtropical habitats in Africa, Southeast Asia, and Australia, but it’s been in southern Florida for many decades and has been infesting areas of the Everglades since at least 1965. By 2003, the infestation reached at least 150,000 acres in total extent. Some areas of Everglades National Park are already infected.

The NPS is very concerned about the implications for the park. And no wonder! People who know what this exotic plant is and what it can do to the ecosystems it invades can’t help but feel a sense of dread.

You have to give the darn thing credit for being amazingly adaptable. Blown by the wind, its spores can infect new areas up to 40 miles away. It’s not real choosy, either. It can grow in sawgrass prairies, marshes, piney woods, hardwood hammocks, cypress sloughs, tree islands, mangrove swamps, roadside ditches, and a variety of other habitats.

Once established, it grows rapidly and lives for a long time. Unfortunately, this rapidly spreading menace not only extends horizontally, but also climbs into the uppermost branches of trees, sometimes reaching as high as 90 feet. Spreading laterally in the canopy, it covers the underlying branches and leaves with a dense mat that can be up to three feet thick in places.

The effect on native vegetation can be positively devastating. Plant diversity plummets in seriously infected areas as the understory vegetation is overwhelmed and whole stands of trees are smothered. Even rare plants are not spared by this relentless aggressor.

One of the more dangerous impacts of this nasty plant is the heightened risk of fire damage to trees. Ground fires that might otherwise yield generally beneficially results can end up being extremely destructive crown fires because the invader provides a “ladder” for the fire to reach into the canopy. Once there, the blanketing mat provides fuel as well as burning masses that may be spread by the wind to start new fires.

Even bald cypress trees growing in standing water can be placed at risk in this way. Whereas ground fires stop at the edge of cypress sloughs, being unable to advance because of the soggy ground or open water, crown fires can sweep through cypress trees infected with the lime-green menace and severely damage or kill them.

Controlling this dangerous invader is anything but easy. Once the plants are established, you can’t get the upper hand by simply severing the fronds wrapping around tree trunks and extending into the canopy. The plant will simply regrow if you do that, and you will get the same result if you try hand-pulling or burning. You can kill the plant with herbicides (assuming that’s feasible), but you still have to get rid of the dead material -- a time-consuming and expensive task – while taking great care not to release vast quantities of spores that can spread the infection. Leaving the dead material in place is not a good option, since the mat inhibits the growth of understory vegetation, starves trees of sunlight, supplies fuel for fires, and provides a means for fire to reach into the canopy.

Unless something is done soon (a self-sustaining biological control?) this nightmarish invader could cancel out efforts to restore the Everglades ecosystem to some reasonable semblance of health. Scientists are especially worried that the invader may have a ruinous effect on the native plants and animals inhabiting the vulnerable hardwood hammocks and tree islands.

Nearby Big Cypress National Preserve is infected as well.

Can you name this dangerous plant pest?

Answer: It’s the Old World climbing fern (Lygodium microphyllum), which is sometimes called (in addition to simply Lygodium) the snake fern, the small-leaved climbing fern, or the climbing maidenhair. See the Bugwood Network website for detailed information about the OWCF. An integrated management plan for the OWCF devised by the Florida Exotic Pest Plant Council Lygodium Task Force (2nd edition, 2006) can be viewed at this site.

Comments

As I try to clear vines and honeysuckle from overgrown gardens and cut down treees that have grown up I recall that Leif Erickson wanted to call this land " Vineland" I think that is very appropiate. It is an exhausting struggle to clear vines and this seems to a similar situation. Kudzu has taken over vast track and I saw a show on using sheep to graze the areas down and the use of border collies to round them up. The persn trailers sheep to an area and then another area just to keep thes pest from infesting areas.

Kudzu is a whole 'nuther matter, RAH. Being a South Carolina resident, I'm thoroughly familiar with "the plant that ate the South." Some people say that you can only kill kudzu by driving a stake through it's heart, but I suspect that may be an exaggeration. I've seen goats used for kudzu control, but this is the first I've heard of sheep being used for that purpose.

Well I may have been wrong and it was goats. it was while since I saw that show. I have not heard about this climbing fern before but reminded me of kudzu which has reached MD now. This is just nature at its worst or best with a new interloping sucessfully crowding out existing lifeforms.

The qustion is do we want to try and bring it back to it's past or adapt to the new situation? This is the eternal question of parks. We had gypsy moth infestations and pine beetles. Mankind has been struggling since existence fighting against nature and in the most we have suceeded.

It is amazing to me to see orderly farmlands revert to scrub and then forests. Volacanoe ravaged areas spring back with new growth. Life is determined to survive.

I remember this plant when I lived down south. It was all over, but most times you could see the hanging vines from where people were cutting it down to make use in home decorations. I pulled up a website for this blanket vine and found many people harvest this plant for not only medicinal purposes but for design as well. Is there a way that we can also harvest this plant to the benefit of our nation? I also read there is yet any type of "killing device" for this plant. So then, how does Japan and China, which this is most native to, keep theirs "under control"? There has got to be a way. The goats sounds great, but goats can be as invasive as well. Also, thriving in the Everglades may damper a "harvest" as it wouldn't be an easy thing to acquire. I just wonder why we haven't gone to the "source" to find out how to "control" this thriving if invasive plant.

You'll have to forgive my ignorance in my previous comment. I found there is also much research going on to find a "killer" for this plant. I read scientists and biologists have been working on finding natural enemies of this plant in many of the areas where it originated from. On that note, I will remember to learn before I speak.

I won't hold you to that promise, Donna. If they ever start enforcing a "learn before you speak" rule here at NPT, I'll be out of business!

Sorry I'm late to this party: our connection to the rest of the internet died again yesterday.

If you want to see a graphic image of Lygodium collapsing and killing a tree island, look at:
http://bio.fiu.edu/lygodium/images/DSCN1108.jpg I shot this in the Loxahatchee NWR not Everglades National Park. Currently, on the order of 1/3 or 1/2 of the tree islands in Loxahatchee are infested with Lygodium. Lygodium is still sparse in ENP: a few patches in Brazilian Pepper (itself another exotic invasive species) and mangroves on the western park of the park. [The last I knew, there actually is more Lygodium in Big Cypress than in ENP.] Tony Pernas and Jonathan Taylor of NPS deserve credit.

While Lygodium _can_ grow on sawgrass, marshes, ditches, and prairies, it doesn't grow very large there. It grows large and produces billions of spores when it climbs on trees. The reason folks are more scared about Lygodium than about Melaleuca or Australian Pine (Casuarina) or Brazilian Pepper (Schinus) or even kudzu (not a problem in south Florida) is that for the other exotic species, control actions can start on one side and roll back the infestation, because seed dispersal isn't that great. Melaleuca is "officially" extirpated in ENP because they first went after the small outlying patches that served as seed sources or foci of further spread, then they systematically went after the solid stands on the edges of the park. Lygodium doesn't have local dispersal: the spores that started the infestations in the southwest part of ENP likely blew in from Loxahatchee, 40-75km away. Therefore, Lygodium must be controlled over very large areas simultaneously.

This report is a bit out of date in the last comment about biological control. Bob Pemberton of USDA in Davie is pretty far along in testing biological control agents (a weevil and a rust fungus). However, the patchy "islands" of habitat (tree islands, bay heads, etc.) are a major problem for biological control to be effective. Lygodium produces billions of spores, which disperse very long distances, so almost every tree island receives new spores every month, and new Lygodium infestations can pop up anywhere. Effective passive biological control would require a control organism that can colonize new patches of Lygodium at least as fast as Lygodium colonizes new tree islands: a pretty tough race against a fern with spores. My little project on spore germination & growth requirements and a bit of math suggests that biological control may be feasible, but not self-sustaining: someone is likely to have to culture the rust and weevils and release them on 5-10% of the tree islands each year.

Thanks for the information and that amazing photo, Anon. There's clearly a lot more to this Lygodium business than meets the eye. I'll watch for updates and hope that some sort of breakthrough will soon happen on the biological control front. Meanwhile I've made a few edits to the article based on the new-to-me information you've supplied. I never cease to be amazed at the breadth and depth of NPT reader expertise.