Flower:

Flowers are single in leaf axils along branching stems, trumpet-shaped, about 1 inch diameter with 5 spreading lobes, on a slender stalk that may be longer than the attending leaf. Flower color varies from blue to violet, sometimes white. The calyx cupping the flower has 5 narrow lobes shorter than the floral tube. Inside the tube are 5 stamens and a green style.

Leaves and stems:

Leaves are opposite, evergreen, leathery, lance-elliptic to egg-shaped, ½ to 2 inches long, up to 1 inch wide, toothless, hairless, blunt to pointed at the tip, and on a short stalk. New leaves may initially be bright green, the upper surface becoming shiny dark green, the lower more silvery. Stems are woody near the base, may reach 6 feet long but creep along the ground, rooting at the nodes and forming dense mats; flowering branches more erect but rarely exceed 8 inches tall.

Fruit:

A flower may produce a pair of slender bean-like pods ¾ to 1 inch long, each containing a few seeds, but fruit is rarely produced.

Notes:

Periwinkle is a European introduction long touted in the nursery trade as a tough, fast-growing ground cover; there are a number of cultivars bred for flower color and/or variegated leaves. It can escape cultivation and is particularly problematic in woodlands, where it can form dense mats and crowd out native species; it is currently considered invasive in Wisconsin. One report from Indiana noted it covering acres of native forest forming a stand so dense it excluded nearly all other vegetation, including reproduction of the trees. It's only been recorded once in Minnesota, escaped from a cemetery planting in Rice County, but is likely under-reported here.

Periwinkle is recognized by its low-growing form with creeping stems; shiny, evergreen, opposite leaves; stalked flowers single in the leaf axils, typically blue to violet with 5 spreading lobes; fruit is a pair of bean-like pods but are rarely produced. The flowers resemble those of a Phlox, which have a terminal cluster of flowers; all of the native Phlox in Minnesota have erect stems, not creeping. The leathery, evergreen leaves vaguely resemble some low-growing members of the Ericaceae family, such as Wintergreen (Gaultheria procumbens) or Bearberry (Arctostaphylos uva-ursi), which have alternate leaves, clusters of small bell-shaped flowers, and typically abundant bright red, berry-like fruit.