Shrubby St.John's-wort is a tall, densely branched shrub with sharply 2-edged twigs.
Flowers are in small groups (cymes), showy, 5-parted with abundant stamens, yellow. Blooms June–September.
Leaves are opposite, narrowly elliptical, abruptly narrowed toward base, to 2½ inches long, sessile, shiny, somewhat leathery.
Fruits are capsules about ¾ inch long, splitting at the tip, with numerous small seeds.
Similar species: There are 14 species of Hypericum in Missouri. They all have opposite, simple, entire leaves with small resin dots, and flowers with 4 or 5 yellow petals, 4 or 5 sepals, many stamens, and 1 pistil. Many are small shrubs, with twigs often angled or 2-winged. Fruits are capsules with numerous seeds. They bridge the gap between "woody" "nonwoody" plants, and many can easily be classified as "wildflowers," demonstrating that putting plants into these categories is less than satisfactory.