St. John's Wort family (Hypericaceae)
Description: This perennial plant is up to 2½' tall, branching frequently from the upper axils of the leaves, and having a shrubby appearance. The base of the plant is occasionally semi-woody, but the upper stems are herbaceous and green. The entire plant is devoid of hairs. The opposite leaves are up to 3" long and ¾" across. The pairs of leaves rotate by 90° as they ascend the stems. They are oblong or lanceolate with blunt tips, and are sessile against the stems. The margins are smooth, while the underside of each leaf is light green and devoid of black dots.
Numerous clusters of yellow flowers occur at the ends of the upper stems. Each flower is about ½–¾" across, with 5 rounded petals, and numerous long stamens surrounding a stigma that is slender and flask-shaped. The flowers have a mild buttercup-like fragrance. The blooming period occurs from early to mid-summer and lasts about a month. The small seeds are distributed to some extent by the wind. The root system consists of a central taproot and short rhizomes. This plant tends to spread vegetatively in sunny open areas.
Cultivation: The preference is full or partial sun, and average to dry conditions. Different kinds of soil are readily tolerated, including those with substantial amounts of loam, gravel, sand, or clay. However, poor soil is often preferred because of the reduced competition from taller plants.
Range & Habitat: Round-Fruited St. John's Wort is widely distributed in Illinois, but it occurs only occasionally (see Distribution Map). It is least common in SE Illinois. This is a native wildflower. Habitats include mesic to dry gravel prairies, sand prairies, hill prairies, rocky open woodlands, thickets, scrubby barrens, rocky bluffs overlooking major rivers, limestone glades, dry banks of lakes, and open areas along roadsides.
Faunal Associations: Bumblebees and other long-tongued bees are probably the most important pollinators of the flowers. Other visitors include Halictine bees, beetles, and Syrphid flies, but they are less effective at pollination. All of these insects collect or feed on the abundant pollen, because the flowers offer no nectar. The caterpillars of the butterfly Strymon melinus (Gray Hairstreak) reportedly eat the seed capsules, although it is not a preferred host plant. The caterpillars of the moth Nedra ramosula (Gray Half-Spot) feed on the foliage. Like other St. John's Worts, the foliage of this species contains a toxic chemical that causes photosensitive skin reactions, particularly in light-skinned animals, and can irritate the gastrointestinal tract. Therefore, mammalian herbivores usually leave this plant alone if other food sources are available.
Photographic Location: The photographs were taken at Crystal Lake Park in Urbana, Illinois.
Comments: This plant can be easily distinguished from similar St. John's Worts by the absence of black dots on the flower petals and undersides of the leaves. The flowers tends to be larger than Hypericum punctatum (Spotted St. John's Wort), but smaller than Hypericum kalmii (Kalm's St. John's Wort), and Hypericum pyramidatum (Great S. John' Wort). This is an attractive plant while in the early to middle stages of bloom, although later losses some of its appeal because of the persistance of older brown petals near the seed capsules.