A nonwoody, erect plant with a smooth stem and milky sap, and 2 to 6 pairs of opposite, narrow, tapering leaves. This perennial plant blooms from late May to mid-June, producing one or two cluster of flowers at the top of its stem. Each cluster has an average of 5 to 14 flowers. The flowers are yellow-green or greenish-cream and are often tinged with purple. Individual flowers have five tubular hood-shaped structures with a slender "horn" extending from each one.
Seeds mature from July to October. Pods are green and gradually become darker as they mature, growing to be 1 1/2 to 4 inches long. A single plant may have multiple stems, which can be mistaken for individual plants. Each stem produces flowers for 2 to 3 years and then becomes dormant or disappears.