This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Tall perennial herbs, with large ternately divided or 2-pinnate leaves, sheathing petioles, and compound umbels of white flowers. Calyx-teeth obsolete. Petals ovate, mostly emar-ginate. Fruit much flattened dorsally, broadly oval, to nearly orbicular, cordate at both ends, the lateral ribs broadly winged all around, the intermediate and dorsal ribs slender, wingless; oil-tubes solitary in the intervals and 2 on the commissural side. Styles and conic stylopodium short. Seed-face flat. [Named for its supposed forceful medicinal properties.]
About 10 species, natives of the Old World, the following typical.
Imperatoria Ostruthium L. Sp. Pl. 259. 1753.
Glabrous, or sparingly pubescent; stem stout, hollow, erect, 2°-5° tall. Leaves ternately divided into very broad stalked ovate to obovate segments, which are often 3-parted nearly or quite to the base, sharply and unequally serrate and often incised, the segments of the long-petioled lower leaves often 5' broad; rays of the umbels and pedicels very numerous, slender; involucre none, or of 1 or 2 lanceolate bracts; involucel-bracts few, narrow, deciduous; fruit broadly oval, about 2" long.
In fields, Pocono plateau of Pennsylvania. and Michigan. Reported from Newfoundland. Naturalized or adventive from Europe. Broad-leaved hog's-fennel. Felon-grass. Imperial masterwort. Fel-onwort. May-July.