Part I: Plants
By Susan Rothrock Deo
Do you have dandelions in your yard? Most grownups call them weeds because they grow where we don’t want them. We kids know better—dandelions are AWESOME! Pretty yellow flowers, puffy heads of floating seeds that scatter in the wind. The dandelion, originally from Eurasia, is an example of a non-native species that has found its way to Southern California.
For millennia species have been on the move. Some carry themselves, wind and water carry more. Humans are notorious for transporting species from afar to grow for their beauty or for food. Sometimes we move things accidentally, like when sailors of old brought their mattresses ashore and shook out the old straw bedding (including seeds and insects) to replace with fresh dried grass.
Most non-native, or “alien,” species are not a problem in their new homes. Some are even beneficial, like corn or almond trees. Trouble occurs when an alien species causes economic or environmental harm, or harm to human health. Then its INVASIVE. Harmful invasions are usually caused by species from similar climates that travel well, grow and reproduce vigorously. They may out-compete or prey on native species or disrupt the native habitat. Most do not benefit their new ecosystems, such as becoming food for native species. Here are a few of the plants scientists have designated invasive in Southern California.
Castor bean, Ricinus communis, was cultivated for castor oil and as an ornamental. The plant is extremely poisonous. Two seeds can kill a human.
Fennel, Foeniculum vulgare, related to anise and licorice, was brought from southern Europe as an herb for cooking and medicinal purposes. It is very hard to eradicate. Where naturalized, however, scientists must consider the Anise Swallowtail butterfly first. Fennel is their preferred food, so if all the fennel is removed, their population will suffer.
Pampas grass, Cortaderia selloana, is a landscaping plant originally from South America. One plume can produce 100,000 seeds or more that travel far on a windy day. It may look nice in your neighbor’s yard, but you can also see pampas grass scattered along the bluffs all the way up the coast. Non-native grasses like this crowd out our native bunch grasses. Native grasses are much more fire-resistant and are better food for local species.
Russian thistle, Salsola tragus, is one of several species we call “tumbleweed.” Seeds were first brought from Russia to South Dakota in a batch of contaminated flax seeds in 1873. Dried plants break off at the base and the ball-shaped plants tumble along dropping seeds as they go, thus tumbleweed spread throughout the West. (It didn’t arrive soon enough to be part of the old West’s story as Western movies and fiction portray, though.) Recently, a new tumbleweed has appeared in California. Because it’s a hybrid of two species it has no native range and scientists are having trouble finding insect pests to help control its population.
Want to learn more? Pick up a plant field guide or search online for invasive species. Next time, non-native and invasive animals!