|Section:||H. sect. Myriandra|
|Subsection:||H. subsect. Centrosperma|
|Known occurrences of Hypericum swinkianum|
Swink's St. John's wort is a many-branched shrub up to 1.8 meters (5.9 ft) high. It has exfoliating bark. The leathery, oblong leaves reach 2 centimeters (3⁄4 in) in width and 5 centimeters (2.0 in) in length, with weakly revolute edges. The flowers are produced in terminal flowerheads known as dichasia. Each dichasium produces 7-31 bright yellow flowers, each with 5 petals and numerous yellow stamens. The capsules are 5-parted. In the Chicago Region, it blooms between July and August.
Hypericum swinkianum differs from the closely related Hypericum kalmianum by its notably larger vegetative features, flowerheads each averaging more than 7 flowers, and an affinity toward acidic rather than calcareous habitats.
Distribution and habitat
Swink's St. Johns wort is known to occur in sand flatwoods and acidic wet to wet-mesic sand prairies in the western Great Lakes region in the United States, including Illinois, Indiana, and Michigan. It is a highly conservative species with a coefficient of conservatism of 10 in the Chicago Region and in Michigan.
- Wilhelm, Gerould; Rericha, Laura (2016). "A new species of Hypericum (Hypericaceae) and some new combinations in the vascular flora of the Chicago Region" (PDF). The Michigan Botanist. 55: 89–96.
- "Hypericum swinkianum". Michigan Flora. Retrieved 2018-12-11.
- Wilhelm, Gerould; Rericha, Laura (2017). Flora of the Chicago Region: A Floristic and Ecological Synthesis.