Cow Parsnip (Heracleum maximum)

 

Cow Parsnip (Heracleum maximum)

Cow parsnip (Heracleum maximum) is a tall, native wildflower found across North America, including Wisconsin. It typically grows 4 to 10 feet tall and bears broad, flat‑topped compound umbels of small white flowers, each umbel spanning 4 to 12 inches across. Individual flowers are about a quarter inch wide, with larger, showier blossoms often forming a lacy ring around the edge. The leaves are enormous and divided into three large lobes or leaflets, with basal leaves reaching up to 18 inches long and wide; their surfaces are softly hairy and coarsely toothed. The stem is thick, hollow, ridged, and covered in fine white hairs, sometimes approaching 2 inches in diameter. Cow parsnip thrives in full sun to partial shade in moist, nutrient‑rich soils, especially along streambanks, forest edges, wet meadows, and cool alluvial flats. Its sap contains furanocoumarins that can cause skin irritation when exposed to sunlight, making it a plant best admired without handling. Ecologically, cow parsnip is an important summer nectar source, supporting a wide range of pollinators—including bees, flies, beetles, and butterflies—drawn to its abundant, accessible umbels.

Sources:

USDA PLANTS Database — Heracleum maximum species profile

Minnesota Wildflowers — Heracleum maximum (Cow Parsnip)

Illinois Wildflowers — Cow Parsnip (Heracleum maximum)

Flora of North America — Heracleum maximum botanical description

Michigan Flora / University of Michigan — Heracleum maximum account

NatureServe Explorer — Heracleum maximum conservation status and distribution

UW–Madison Division of Extension — Native wetland and riparian plants of Wisconsin

(LS)