To me, one of the quintessential summer-blooming wildflowers is the common St. John’s wort. By, or shortly after the summer solstice, you should start to see its sunny yellow blossoms everywhere. Common St. John’s wort (Hypericum perforatum) can be distinguished from other Hypericum species by its five-petaled yellow flowers (with black dots on the margins) that are approximately 1-inch across, and its many branching stems, growing to a height of 1 to 3 feet, as well as its oblong oppositely arranged leaves, which when held up to the light, display numerous tiny dots that appear to be perforations. While these dots provided the inspiration for this plant’s species name, they are actually a translucent layer of oil glands. 

Common St. John’s wort flowers – note the black dots at the margins of the petals. 

Common St. John’s wort leaves – tiny perforation-like dots are visible when held up to the light.

The common name of this plant is a tribute to St. John the Baptist, as the plant typically blooms near his birthday (June 24th) and the red oil produced by the flower buds and seed pods is said to represent the blood spilled upon his beheading. 

Although native to Europe, common St. John’s wort is now widely naturalized across much of temperate North America and is common in fields and meadows, as well as along roadsides and forests. Common St. John’s wort has been used for centuries in folk medicine to treat a variety of medical conditions. It is still widely used today in herbal medicine as an antidepressant, and is well-known for its ability to relieve anxiety and tension. Although the flowers can be harvested when in full bloom and dried for tea for this purpose, caution is warranted when using this plant due to its potential interactions with other medicines. It has been shown to reduce the effectiveness of other drugs, including oral contraceptives, anti-epileptic medications, and some antibiotics, as well as others.