Flower:

Small clusters of flowers at the end 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 are sharply pointed and 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 Hypericum canadense (Lesser Canadian St. Johnswort), generally a smaller plant with only 1 distinct vein on the leaves, but it's debatable whether that species grows in Minnesota. Various sources say it is native to MN but there are no records of it in the Bell Herbarium. It may be that historical records of it were in fact H. majus. All Hypericum species have switched from the Clusiaceae family to Hypericaceae.