July and August Native Maryland Plants
Hypericum densiflorum Pursh.
(hy-PER-ee-kum den-see-FLOR-um)
Common Name: Dense St. John’s Wort
Hypericum prolificum L.
(hy-PER-ee-kum pro-LIF-ih-kum)
Common Name: Shrubby St. John’s Wort
This month I want to share with you two plants that are commonly confused with one another: Hypericum densiflorum and Hypericum prolificum. By discussing them side-by side I hope to show you how to differentiate them if you ever see them in your work or travels. These Hypericum spp. bloom all summer long, are native to the Mid-Atlantic states and are very low maintenance. Four years ago I planted a single specimen of each so I could learn to differentiate them; I sited them near each other along my driveway where they get full unobstructed sun and no maintenance. They have been blooming profusely since early June and because of their proximity to one another are easily distinguished.
At first glance you notice that both the flowers and the leaves of H. densiflorum are noticeably smaller than those of H. prolificum and there are more flowers to each inflorescence. True to its name, the habit and flowering of H. densiflorum is a much denser shrub with flowers that are tightly clustered. H. prolificum has a more open habit with slightly larger flowers that grow in less crowded clusters on a stem. The stems of each plant are worth a closer look: H. densiflorum is smooth and copper colored while mature H. prolificum appears woody and exfoliates in winter, exposing a light brown to orange bark.
Each plants’ flower has five petals and countless long yellow stamen that give the flower a frilly look -they can even obscure the petals. These flowers contain pollen but no nectar so bees are common visitors, butterflies are rare. Interestingly, both shrubs are a host plant for the gray hairstreak butterfly (Strymon melinus) and several moths. These Hypericum species leaf out early and are teeming with bees as soon as they get a single bloom. They are often planted as erosion control plants; they have good drought tolerance and can easily be pruned to contain their height, if desired.
NOTE: Foliage contains a phototoxic chemical which deters deer and other herbivores. Rutgers rates this plant a B: Seldom Severely Damaged by deer: https://njaes.rutgers.edu/deer-resistant-plants/
~ Alison Milligan – Mstr. Gardener/Mstr. Naturalist/Mstr. Watershed Steward
Chesapeake Bay Landscape Professional (CBLP)