St. John's Wort
St. John's Wort family (Hypericaceae)
Description: This shrubby perennial wildflower is abundantly branched and 2-4' tall. The lower stems are woody with shredded gray-brown bark, while the upper stems are green and slightly winged on opposite sides. The opposite leaves are up to 3" and ¾" across (usually about one-half this size); they are linear-oblong to oblong-elliptic in shape, smooth along their margins, and hairless. The upper surfaces of the leaves are medium green, while their lower surfaces are pale green; they are sessile or taper to short petioles. The upper stems terminates in small clusters of 3-7 flowers; additional clusters of flowers may appear along the 2 upper pairs of opposite leaves. Each flower is ¾–1" across, consisting of 5 yellow petals, 5 green sepals, a pistil with 3 united styles, and abundant stamens. The petals are much larger than the sepals.
The blooming period occurs during the summer and lasts about 2 months. Each flower is replaced by an ovoid-lanceoloid seed capsule about 1/3–1/2" (8-12 mm.) in length. At the apex of each seed capsule, the tips of the 3 styles persist and become separated. Each seed capsule is divided into 3 cells and divides into 3 parts at maturity to release the seeds. The small seeds are narrowly oblongoid, flattened, and black. The root system is woody and branching.
Cultivation: The preference is full or partial sun, moist to dry-mesic conditions, and somewhat barren rocky ground. This shrubby wildflower is readily cultivated in gardens.
Range & Habitat: The native Shrubby St. John's Wort is occasional in the southern half of Illinois and largely absent in the northern half of the state (see Distribution Map). Habitats include upland prairies, upland rocky woodlands and bluffs, rocky stream banks, edges of swamps, abandoned fields, pastures, and roadside embankments. Some local populations near urban areas may be escaped cultivated plants.
Faunal Associations: The flowers are cross-pollinated primarily by bumblebees, which collect pollen for their larvae. Other insect visitors that seek pollen from the flowers include Syrphid flies and Halictid bees, but they are less effective at cross-pollination. Sometimes butterflies and wasps land on the flowers, but they are vainly seeking nectar -- the flowers offer only pollen from the abundant stamens as a floral reward. Insects that feed destructively on Shrubby St. John's Wort and other Hypericum spp. include the aphid Aphis hyperici and other aphids, the leafhoppers Erasmoneura margaritae and Erasmoneura rubricata, Paria sellata and other leaf beetles, caterpillars of the butterfly Strymon melinus (Gray Hairstreak), caterpillars of Nedra ramosula (Gray Half-spot) and other moths, and Clastoptera hyperici (St. John's Wort Spittlebug). The Insect Table lists these species and many others. Most mammalian herbivores avoid consumption of Hypericum spp. because their foliage contains varying amounts of the phototoxic chemical, hypericin. In the presence of light, this chemical can cause rashes to develop on light-skinned animals and it can irritate the gastrointestinal tract.
Photographic Location: A flower garden at the Arboretum of the University of Illinois in Urbana, Illinois.
Comments: Shrubby St. John's Wort has attractive flowers and foliage. It differs from many other Hypericum spp. by its woody lower stems. It is easy to confuse this species with the woody Hypericum kalmianum (Kalm's St. John's Wort), which is restricted to sandy areas near the Great Lakes (including Lake Michigan in NE Illinois). This latter species has 5-celled seed capsules with 5 style-tips, while Shrubby St. John's Wort has 3-celled seed capsules with 3 style-tips. There are also species of St. John's Wort that have 1-celled seed capsules with singular style-tips; some of these may be slightly woody at the base. A widely cultivated woody species, Hypericum frondosum (Golden St. John' Wort), has larger flowers (greater than 1" across) and wider leaves (greater than ¾" across) than Shrubby St. John's Wort. Golden St. John's Wort is native to the southeastern states, but not Illinois. Another scientific name of Shrubby St. John's Wort is Hypericum spathulatum.