Flower:

Clusters of several to many flowers at the ends of mostly erect, branching stems. Individual flowers are ¼ to 1/3 inch across with 5 yellow petals alternating with 5 narrow green sepals, and a cluster of 12 to 20 erect yellow stamens in the center. The sepals taper to a sharply pointed tip and are longer than the petals.

Leaves:

Leaves are ¾ to 1½ inches long, up to about 1/3 inch wide, toothless and hairless, with 3 or more distinct major veins, oppositely attached and often pointing upward. Leaves have a blunt or pointed tip, usually a rounded base, and no leaf stalk, somewhat clasping the stem; the basal edges of the leaf pairs just barely touch around the stem. Stems are ridged.

Fruit:

Fruit is a maroon to purplish conical capsule about ¼ inch long with the remains of the pistil at the top. The fruit is longer than the sepals, which fold up around it.

Inside the capsule are minute, yellowish cylindrical seeds that resemble an ear of corn.

Notes:

A similar species is Northern St. Johnswort (Hypericum boreale), which has proportionately broader, more oval leaves, less densely flowered clusters, leafy bracts on the flower clusters, and sepals that are more oblong with blunt tips. H. majus has no leafy bracts, narrower leaves, and sepals tapering to a sharp point at the tip. Another similar species is Lesser Canadian St. Johnswort (Hypericum canadense), generally a smaller plant with only 1 distinct vein on the leaves, but it's debatable whether that species exists in Minnesota. Various sources say it is native to MN but there are no records of it in the Bell Herbarium, and the DNR does not recognize it as existing in the state either. It may be that historical records of it were in fact H. majus. All Hypericum species have switched from the Clusiaceae family to Hypericaceae.