June - October
0.4 - 0.9
May be confused with Hypericum hypericoides which is the only other prairie species with four petals. H. crux-andreae may be distinguished by its flowers which have 3-4 styles, and its leaves which are oblong-elliptic, the upper ones clasping, while Hypericum hypericoides has two styles and linear to oblong-oblanceolate leaves that are narrowed at their base. The Hypericums have punctate or gland dotted leaves that are opaque if held up to the light.
Seed germination is improved by cold/moist stratification (Steffen 1997).