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U.S. Forest Service

Plant of the Week

USDA Plants distribution map for the species. Range map of Polymnia canadensis. USDA PLANTS Database.

Whiteflower Leafcup (Polymnia canadensis) A large, rank plant. Photo by David D. Taylor.

Whiteflower Leafcup (Polymnia canadensis) Head of flowers beginning to open. Note six ray flowers with stigmas. Photo by David D. Taylor.

Whiteflower Leafcup (Polymnia canadensis) Late summer seedling showing leaf shape. Photo by David D. Taylor.

Whiteflower Leafcup (Polymnia canadensis L.)

By David Taylor

Whiteflower leafcup is a member of the Asteraceae, the Sunflower family. In older manuals and guides, this family is called the compositae because the 'flowers' are a composite of many flowers, often of different types. The many species of plants in this family are grouped based on the arrangement and type of flowers. All members of the family produce one or more heads (capitulum, the term used in technical keys) of flowers. Flowers in this family can be either ray flowers (these are the white 'petals' of a daisy) or disk flowers (the yellow center of a daisy). This plant produces both kinds of flowers. Three species are recognized in North America.

Whiteflower leafcup is 0.5 to 1.5 meters (18 to 60 inches) tall. The stem is somewhat weak with soft, sticky hairs on it. The plants are frequently much branched and floppy. The opposite leaves form a small cup around the stem and hence the name leafcup. The lower leaves are pinnately lobed. The entire plant has a strong resinous odor when crushed. Leaves are pale green, lighter below with short hairs scattered across the veins and leaf surface. Leaves are 10 to 20 cm (4 to 8 inches) long about 12 centimeters (4.5 inches) wide. Heads are in small clusters at the end of branches. Each head has 0 to 5, rarely 6, white ray flowers to the outside, and 12 or so yellow tube-like disc flowers to the inside. In the photo to the right, the stigmas are visible in the ray flowers, and the stamens are visible in the disc flowers. Only the ray flowers produce seeds. A single large plant may produce one hundred or more heads.

This leafcup is a species of usually moist, shady forest on calcareous soils. The plant may be annual or perennial. If perennial, seedlings often produce large leaves the year before flowering (see photo to the right). This species is found from Minnesota south to Arkansas, east to New York, Vermont and Connecticut, south to Georgia, except for Mississippi, Florida, South Carolina, New Jersey, and Delaware. It is also known from Ontario.

This species flowers in May to September, into October if frost holds off. It is an excellent nectar plant and is visited by many species of bees and wasps.

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