Emerging Invasives
Cheilanthes viridis, the green cliff brake fern, is growing wild in Houston natural areas and most aren't even aware. And it isn't the only emerging invasive species on the horizon.
Every region is home to an invasive species. What is native here in Texas is invasive somewhere in Africa. And vice-versa. We can thank hundreds of years of the horticulture and agriculture trade for introducing flora and fauna, both intentionally and by accident, to our ecosystems. Here in Greater Houston, where I live, we have everything from Chinese tallow, Japanese and Chinese privets, taro, cogon grass, Brazilian pepper and Brazilian vervain, King Ranch bluestem, island apple snails, nutria, and beyond. And plenty more that aren’t characterized formally as invasive, but actually are once you start noticing them (because limited budgets and personnel can’t stay on top of it all): I’m looking at you mulberry weed and chamberbitter!
What is an invasive species?
Contrary to what many people will say, and what you will hear used colloquially in the gardening world, it does have a definition.
Executive Order 13112 defines an invasive species as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” In the Executive Summary of the National Invasive Species Management Plan the term invasive species is further clarified and defined as “a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” - From Invasive Species Advisory Council
I frequent Kleb Woods Nature Preserve in far NW Harris County fairly frequently because it is a natural area that is relatively easy for me to get to from where I live and work. It isn’t the most pristine ecosystem, having been the former homestead of Elmber Kleb who farmed on the land with his family until, long story short, he became a hermit and was unable to pay his tax bills. Eventually the county was able to purchase the property and allow him to live on the land until his death in 1999.
The park has several hiking trails, a nature center and butterfly garden, as well as a museum of sorts of Elmer’s old homestead, including plenty of antique farm equipment. The staff at the nature center also keep up an edible garden and I always enjoy seeing various plants that are grown there from cotton to luffa to okra and much more, including, until February 2021’s Snowpocalypse, several mature citrus trees. Much of the property is in somewhat of a natural state after having been cleared and farmed in the early and mid-20th century. Loblolly pines tower above the property and there are several bottomland or wetland areas with interesting natives. Entwined in these wetlands are the invasive Chinese tallow tree, and there are several large live oaks at the southern end of the property. The understory is dominated by yaupon holly and the property is in need of a good burn, which won’t happen because of the increased encroachment of the city nearby. Mixed in with the yaupon you can find various non-native privets as well as Japanese climbing fern throughout, and plenty of chamberbitter along the edges of the pathways.
During one of my trips last year I ventured into a cleared area that I had noticed the park had thinned within the previous year or so. I went to poke around to see what I could find to add to the inventory of species on iNaturalist. That’s when I came across many clumps of a fern I didn’t recognize. I thought it was rather pretty and was excited about a potentially interesting native fern that I was unaware of. Oh, little did I know!
Once I identified it as green cliff brake fern, I soon came to find out that this plant is slowly becoming problematic, in Houston in particular, but likely throughout the south. Starting about 8 years ago, some biologists in the region began taking notice of the plant and as the years have gone on more plants have been popping up in wild spaces. Now, Kleb Woods’ problem is that they actually have this fern planted up near their nature center and labeled, as they would any of their other plantings, because this fern is in cultivation at nurseries and garden centers. In fact, one website I found that sells it says, “Easy, deer resistant, suitable for Texas gardens!” Well, imagine that! Now, I don’t know if that clearing at Kleb Woods helped the spread of the fern into that area or if it was already there before they cleared out some of the yaupon, but I do know that I’ve found it in plenty of other places in the park. And it hasn’t taken me long to start finding it in other natural areas, either.
Green cliff brake fern is naturally found in South Africa and up through Tropical East Africa, and some other areas in that general vicinity. It has also become naturalized in other countries such as Australia which already has its fair share of invasive species. Once I pinpointed this species on iNaturalist, I quickly ended up taking a deep dive into the current status of its colonization of North America through a paper called The Status of the Non-Native Fern Cheilanthes viridis (Pteridaceae) in the United States from December 2020 by George Yatskievych. In the paper, the author details the specimens collected from South Carolina all the way to Austin, Texas and includes detailed taxonomic information on how to key the plant out. On iNaturalist you can see that the epicenter for now is in the Houston area, with those handful of specimens in Austin, and a few in Louisiana. I suspect there are plenty more hiding in other southern states because folks just haven’t noticed them yet. I recently found one in Burroughs Park, another Harris County park that borders Spring Creek, that hadn’t had any documentation yet, but there it was. And I’ve also found many plants along a creek in Conroe.
In Houston, sightings are primarily on the north side of Harris County and southern Montgomery County, with a prevalence along natural areas in the Lake Creek and Spring Creek drainages, which all lead to the San Jacinto River. Naturally, it wouldn't take much for floods to spread spores or uproot plants and move them downstream. Of course, not all are along a riparian corridor, such as the plants at Kleb Woods. There, they could easily be managed in a work day or two and yet, they are still there, allowing spores to continue to be released and flying wide into other areas nearby.
This isn’t the first fern to escape. There are plenty of houseplant and landscape ferns that have escaped; Boston fern, Salvinia sp. (a major clogger of waterways), Japanese and Old World climbing ferns—I could go on. This feels like such an early stage that we could do something about it and…not much is going on with it in agencies or even being discussed from what I can tell. Not that I should expect anyone to be doing anything—the Texas response to invasive species is weak at best and typically focused on those affecting waterways. And certainly the horticulture industry won’t do anything about it because they still grow and sell invasive nandina.
My point being, is that you never know what is going to become the next invasive species or when the turning point of being a well-behaved garden plant becomes an invasive exotic, colonizing habitats it doesn’t belong in. What are the environmental costs, and later the economic costs? Maybe if we are lucky this plant won’t expand far beyond Houston, but I doubt it. I think in 10 years it will have spread dramatically. Seeing the maps for locations throughout Houston makes me want to go to each location and dig them up with a shovel—which I would suggest you do if you came across one. Bag it, toss in the garbage.
I do wants to invite you to think about your own gardens for a minute and think about the seedier or runnier non-native species—those that you constantly find moving about the garden into places you didn’t put it. In 10, 20, 30 years, how will they be impacting your local natural areas? Consider your local invasive plant lists and even if it is still available in the horticulture trade, stop purchasing those species (hello nandina!), and remove them from your garden. Even supposed sterile plants are often not nearly as sterile as the horticulture industry proclaims them to be.
By exploring your local natural areas within the state you can become familiar with changing ecosystems. Even if you don’t use citizen science apps like iNaturalist or eBird, taking photographs or making notes will suffice in the long term. You can easily look through previous years to determine how things have changed, when you first noticed a plant or animal within the area and if its population has changed over time. In a world of increasing ecosystem blindness, the more people willing to dive into nature and share it with others, the better.
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