This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Perennial. Propagates by seeds.
Time of bloom: June to July.
Seed-time: August to September.
Range: Labrador to Alaska, southward to North Carolina, Missouri, Utah, and California.
Habitat: Moist ground; waste places, sides of ponds, ditches, and streams.
One of the largest of umbellifers, well named for Hercules, the giant. The huge, fleshy root sends up a stalk four to eight feet tall, sometimes two inches thick at base, deeply ridged and grooved, and wrapped in matted white hair. Leaves large, ternately compound, the segments broadly ovate, sharply toothed, and cut-lobed, stalked, somewhat thin for their size, densely covered on the under side with a network of white, woolly hair; petioles stout, much inflated, and clasping at base. The whole plant has a disagreeable odor, especially when bruised, and the juice is extremely acrid; that of the root, when applied to the skin, will quickly draw blisters. Flowers white, occasionally purplish, the flattened compound umbel sometimes a foot broad; individual flowers often more than a quarter-inch broad, particularly the enlarged outer ones, with the five petals notched at the outer edge; involucre deciduous. Carpels obovate, nearly a half-inch long, flattened, with winged margin and notched apex, the oil-tubes extending only part way down the sides. The weed is dangerous to cattle, when growing about their drinking places, at the time of starting shoots in spring; later they avoid it. (Fig. 213.)
Fig. 213. - Cow Parsnip (Heracleum lanatum). X 1/4.
The plant is persistent because of its large root, which needs to be grubbed out or deeply cut and treated with dry salt or kerosene.