Hypericum perforatum / St. John’s wort

Adjectives: disturbed, exposed, forest openings, interesting bits, invasive, LSRP, non-native, noxious

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August is St. John’s wort’s favorite time, when its bright yellow, star-shaped flowers appear. Each flower has many long stamens that stick out every which way. The flowers are clustered at the tops of stems with 25 or more per individual stem. The clusters actually have multiple branchlets with two flowers at each node.  Both the petals and the leaves have oil glands, especially visible as black or white dots when back-lit and as black lines on the petals (see the gallery photos). The petals are often crenelated (wavy edged).

There are several species of St. John’s Wort in Wydaho and they are not easily distinguishable. After trying to make the one’s shown here into something native and wonderful, even consulting with a couple recognized experts who specialize only in this genus, I’ve failed. I have been forced to admit that this species is non-native, highly invasive and listed as a noxious weed in Wyoming and Idaho. Too bad. The photos here are from the Laurance S. Rockefeller Preserve in Grand Teton. I have not yet seen it west of the Tetons.

H. perforatum  is found in a variety of habitats ranging from riparian to high and seemingly dry. Sometimes, it forms very large patches in large forest gaps (photo in gallery).

The stems, up to 3 feet tall, are rusty-yellow to rosy in color, especially at their woody bases. The bases persist through the winter and sprout new growth with flower buds in the following year; first year growth does not produce flowers.

The leaves are opposite and sessile. They vary in shape but are mostly oval. They range in length from about 0.4 to 1.5 inches and have scattered, translucent dots where the glands are. The edges of both the leaves and the flowers usually have scattered black dots. Crushed, they smell a bit resinous, like balsam.

The St. John’s wort fruit is a capsule about ⅓” across. The seeds are contained in three valved chambers. Interestingly, the capsules contain chemicals that inhibit germination; seeds that separate from the capsule have much higher rates. As shown in the gallery photos, capsules may develop even as flowering continues. They develop from green, to red, to brown.

One reason St. John’s wort is capable of colonizing very large areas is that eEach plant may produce between 15,000 and 35,000 seeds and germination rates are high.

Interesting bits – This species contains a host of bioactive chemicals. The best known are hypericin, pseudohypericin, and hyperforin. These have a sort of cult following, but the concentrations of the chemicals   vary widely depending on the individuals, the population and the microhabitat. Using wild plants for medicinals is not recommended. Also before going off and harvesting these plants, please check out the NIH summary of the uses and safety.