For about eight weeks during the summer, Shrubby St. Johnswort (Hypericum prolificum) is decorated with flowers, like ornaments on a holiday tree in mid-summer.
Each bright yellow blossom has five petals that provide a backdrop to a sphere-shaped burst of stamens, the male reproductive parts of the flowers. Reaching out for a pollen deposit from the very center of the flowers are their female reproductive parts, called pistils.
This gaudy display is attractive to me, but more importantly, it’s a very effective lure for potential pollinators. Bumble Bees are among the most likely visitors and effective pollinators. While they climb around the stamens, eating and harvesting pollen from the anthers at their tips, they also pick up quite a bit of pollen on their hairy bodies. As they forage, pollen on their bodies may be brushed off on the stigma at the tip of a flower’s pistil, setting the wheels in motion for pollination to occur.
Female bees eat pollen themselves, and they also collect pollen to bring back to their nests to feed their larvae. In the photo below, you can see the ‘bee bread’ this female has collected on her hind legs. Quite a haul!
Other bees, like Sweat Bees, also visit the flowers for their pollen.
Flies are also consumers of pollen. Flower Flies (also called Syrphid flies or Hover flies) are among those attracted to this pollen banquet. They may also help with the pollination process, although their bodies are not as hairy as many of the bees.
This bounty of pollen is so successful in enticing insects for whom pollen is an important part of their diet, primarily bees and flies, that Shrubby St. Johnswort doesn’t expend any energy producing nectar, finding it unnecessary to do so.
If the inadvertent pollination activities of these insects provide the expected payoff, this shrub lives up to the designation ‘prolificum’ in its scientific name, becoming ‘very fruitful’. Fruit capsules replace the flowers, eventually opening to release their seeds for dispersal by gravity, or by hitching a ride on a passing animal. These dry fruits are visible throughout winter and into the following spring.
Shrubby St. Johnswort is related to the more well-known Common St. Johnswort (Hypericum perforatum), which is used for many medicinal purposes. Shrubby St. Johnswort shares at least one chemical compound, hypericin, with its more famous relative. Hypericin has a photosensitizing effect on its consumers, that is, it makes the skin of the animal that eats it especially sensitive to the sun, and exposure to sunlight after consumption results in rashes. Producing hypericin evolved as an effective deterrent to animals that might otherwise be tempted to eat this plant, including deer.
Shrubby St. Johnswort is a relatively compact deciduous shrub that can grow to a height of about 6.5 feet (2 meters). It does well in a variety of soils, from dry and rocky to moist, and can tolerate full sun to part shade. Shrubby St. Johnswort is native in the eastern half of the United States, and in the province of Ontario in Canada.
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Eastman, John. The Book of Field and Roadside. 2003.
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Rhoads, Ann Fowler; Block, Timothy A. The Plants of Pennsylvania. 2007
Stearn, William T. Stearn’s Dictionary of Plant Names. 1996