Wednesday, December 9, 2020

A perfect storm of weeds

 A weed is sometimes defined as a plant out of place - or more often an overwhelming mass of plants popping up where we don't want them. It's a definition based on our futile attempts to to remake a landscape into something a human vision of tidiness. To be fair weeds are often exotic plants - invasive species from another continent freed from their usual constraints of competitors and predators. And so, weeds are also bad for our natural ecosystems, not just to our landscaping vanity.

Weeds are mostly plants that are really good at spreading into disturbed habitats. They multiply rapidly, often asexually, and fill vacant ground or the exposed sides of forests. They are a vital part of succession, preserving soil, nutrients and moisture. And so such plants are good for their native ecosystems. Our native grape vines and blackberries, however, can also become a nuisance at the edge of woods, sometimes creeping into yards, and so give the landscaper an ethical dilemma.

A native species of morning glory begins to reclaim an abandoned logging road in Papua New Guinea.

Up north, fastidious weed-haters spend hours in the 

Syngonium (Nepthytis) podophyllum is valued as
a house plant, but it can escape into native woods.
Here it clambers into a conservation area near a
housing development in Florida.

spring and summer pulling up dandelions one-by-one from their lawns, only to have them repopulate the next season from the one that got away, its seeded parachutes having been blown across the yard by a visiting grandchild.

While you in the north can relax during the winter, we in Florida, continue to battle with the "Vines from Hell" that never take a rest. Our nastiest weeds are climbers and creepers that can smother a bush within months, or just as easily march through beds and across lawns. They are vines that not only grow upward, but also on the ground, sprouting roots as they go, and this is where they are most troublesome. A simple vine can be severed at the base and pulled from the trees, but removing the rooted bits of one of these creepers from the soil is a nightmare. We chop them up, pull them up, dig them up, but if we leave one tiny fragment, it will come to life again like the splinters of the broomsticks in the Sorcerer's Apprentice. All it takes is a single node, with a single tiny bud.

Missed bits of Syngonium resprout in an area that
was recently cleared of it.

So in our Florida yards some of our worst weed nightmares are Nepthytis (Syngonium podophyllum), flame vine Pyrostegia venusta), air potato vine (Dioscorea bulbifera), and skunkvine (or stinkvine), (Pedaria foetida). Skunkvine comes from tropical Asia and air potato from tropical  Asia and Africa. Flame vine and Nepthytis come from tropical America. 

The air potato is a member of the true Yam Family (Dioscoreaceae), while sweet potatoes, which are sometimes called yams, are in the Morning Glory Family (Convulvulaceae). Real potatoes are in the Tomato Family (Solanaceae).  Air potatoes can evidently now be controlled by a beetle from Nepal, and so is not seen in Florida quite as much.

There are a couple more that don't climb trees, but are even more adept at creeping horizontally through beds and lawns. The Boston fern (Nephrolepis exaltata), a popular house plant, will escape into moist woods and form dense colonies in Florida. It is a native of tropical regions around the world, and will actually freeze to death if it attempts to escape anywhere near Boston! Marsh pennywort (Hydrocotyle vulgaris), native to Europe and North Africa, can choke out lawn grass, particularly in moist areas near ponds.

One of the most rampant vining weeds in central Florida is Skunkvine, here twining its way through a Ligustrum hedge.

Flame vine is an attractive ornamental vine, 
but it can smother trees and also spread across
the ground, rooting as it goes.


Boston fern seems to be an innocuous house or bedding
plant, but can form thickets in moist woodlands when it
escapes. It extends horizontally through the soil by
slender runners that sprout new plants every few feet.


The flowers of pennywort are in umbels, demonstrating its 
relationship to members of the Carrot Family (Apiaceae or 
Araliaceae). Seed production is not important for local
spreading, but is likely responsible for long-distance dispersal.

Air potato vine is a member of the true Yam
Family (Dioscoreaceae). It clambers into

Air potato vines produce small tubers on their
stems, which fall to the ground and start new vines.
Caution - they are not edible. Photo by Karen Brown;
University of Florida; posted on USDA National
Invasive Species Information Center. 

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