Hypericum perforatum (Common St. John’s wort) and Hypericum punctatum (Spotted St. John’s wort) closely resemble each other, with yellow, five petaled flowers about 1/2 inch in diameter and similarly sized plants (about 1 to 2 feet in height). Both bloom in early to mid-summer. From a distance, they appear identical, but can be distinguished upon closer examination.
The flowers of both species are yellow with black dots. However, the black dots of Hypericum perforatum are present almost exclusively along the edges of the petals, while in the case of Hypericum punctatum, the dots are spread evenly across the petals. Sometimes, streaks can be seen on the interior of petals of Hypericum perforatum, but these are always faint.
The greatest difference between the two species is in the appearance of the leaves. In the case of Hypericum perforatum, lighter colored, translucent dots are scattered across the leaf. If a leaf of Hypericum perforatum is held to a light, the light will be faintly visible through the dots. Black dots are present along the margins of the leaves, particularly on the underside. The leaves of Hypericum punctatum, in contrast, have dark dots scattered across the entire surface of the leaf.