Thursday, July 1, 2010

Common St. Johnswort - The Next Invader?

Common St. Johnswort, Hypericum perforatum, is considered a common plant at Blue Jay Barrens. Primarily scattered through the former crop fields, it occurs as individual plants or in small groups. The flower is easily recognized by the dark spots along the margins of the yellow petals. The stamens seem to explode out like a 4th of July starburst.

This is one of those plants that is not native, but has not shown itself to be aggressively invasive. At least here it’s not invasive. In other parts of the country, especially in some of the western states, Common St. Johnswort is on the lists of serious invasive pests. As a non-native plant, I don’t afford it any special consideration in my management activities. Knowing that it has the potential to become a serious invasive, maybe I should actively work to eliminate it before it becomes a problem.

The leaves have rows of semi transparent spots that let light shine through like a series of sky lights. Within those leaves is a phototoxin called hypericin that makes the plant toxic to many types of animals. Eating the plant can result in a serious skin reaction causing anything from a rash to blisters and open sores. These reactions can occur in humans, so I find it interesting that Common St. Johnswort is so often promoted as a healthy herb to alleviate depression. I guess if you’re busy scratching you forget how depressed you are.

You don’t see the local wildlife paying much attention to this plant. The leaves are usually unblemished by bite marks. I haven’t read of the toxins affecting anything other than mammals, but it’s possible that there’s something in the plant that wards off insects. It could just taste bad. The flowers also don’t seem to attract many insect visitors. There were a lot of these flies around, but they just hovered over the flowers without landing.

After examining several dozen plants, this beetle is the only insect I found on any flower. It seemed to be having quite a time negotiating the stamen filaments as it tried to reach the pollen. Even with the scarcity of flower visitors, Common St. Johnswort manages to produce an abundance of seed every year. I can just imagine the seed that’s building up in the field over the years, suddenly germinating and gifting me with thousands of new St. Johnswort plants. It’s hard to know what set of conditions will turn a benign member of the plant community into a rampaging berserker. It’s just one more thing for me to watch for.

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