Each blade has several prominent veins that diverge sharply from the midvein upward toward the leaf tip and dozens of translucent dots, the hypericin-producing glands. A vertical ridge forms on the internode from the base of each leaf to the node below it, so that the stems have these diagnostic pairs of ridges , rotated 90 degrees from the pair above and below. Each node has a prominent ring around it. There is virtually no resting phase in the development of lateral shoots from the axillary buds of each node along the vertical stem. Leaves along the lateral shoots are half the size of those on the primary shoot, and from their axillary buds form another order of lateral shoots that appear like tufts of very small leaves because the internodes of these shoots never elongate.
Flowers form in cymes on the top of the canopy, and often several flowers are open each day.
The petals are distinctly asymmetrical, irregularly serrated on either the left or the right side. The pistil has three widely spreading green styles.