Purple Thistle

Facts about Purple Thistle

The scientific name for purple thistle is Cirsium horridulum Michaux, and it is a member of the Asteraceae family, which also includes all of the daisies. Purple thistle can be found along the East Coast, from Canada to Florida, and across the Southern Coast, from Florida to Texas. It can have purple or yellow flowers.

The word “horridulum” means somewhat bristly, but for those who come in contact with the sharp knife-like bristles on the plant, bristly is much too gentle a word. The spines are so sharp, in fact, that grazing cattle know well enough to leave the plant entirely alone. Purple thistle was named by Andre Michaux in his book, Flora Boreali-Americana, which was published after his death in 1803.

One of the most interesting characteristics of the purple thistle is its ability to move toward anything which disturbs it. For instance, if you were to touch the flower with your finger, the anthers (pollen producing part of flower) would move and curl themselves toward you in a protective effort. If something as small as an insect should try to crawl along the flower, the anthers would move to curl themselves around the insect, covering it with pollen at the same time. This movement is called a thigmonastic motion. The plant can use the motion to protect itself from intruders.

Purple thistle can grow anywhere from one to three feet high. The flowers often add another six inches or a foot to the height of the plant. Its leaves also have a wide range of lengths, from eight inches to two feet long. The yellow version of the purple thistle is found more along wet, coastal areas, while most of the inland plants are purple.

Purple thistle is a plant much beloved by many gardeners, who, failing to find the wild kind of plant, grow it from seeds in their gardens. It grows well in all types of soils and requires little to nothing in the fertilizer department. Purple thistle is great at self-propagation, which is also one of its problems. It reseeds itself so thoroughly that it is listed as an invasive species in many locations.

Some states have laws about growing purple thistle--these include Arkansas and Iowa. On the other end of the spectrum, the purple thistle is listed as endangered in the states of Connecticut, New Hampshire, Pennsylvania, and Rhode Island. If you do plant this thistle in your backyard garden, be sure to set its boundaries and keep the stocks pruned back. If left alone for a few years, purple thistle would entirely take over your yard.

If you are a lover of butterflies, planting purple thistle in your flower garden will attract many different types of butterflies. For example, it hosts the larvae for the Little Metalmark and the Painted Lady butterflies. Butterflies attracted to the nectar include the Black Swallowtail, Delaware Skipper, Palamedes Swallowtail, Palmetto Skipper, Three-Spotted Skipper, Twin-Spotted Skipper and others. In fact, the purple thistle will also attract bees, beetles, wasps and other kinds of insects.

As you can see, the chances are about 50/50 that you will either love or hate the purple thistle plant. The negative feeling might be based on getting pricked when trying to pick the flower or while trying to make your way through a group of these plants as you walk in nature. For people who do love the looks of the plant, or those who want to attract butterflies, it may be a perfect choice for the backyard garden. Just remember to wear gloves when weeding or pruning the plant, and don’t let its growth become invasive.