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 erect mostly biennial branching herbs, with thick roots, pinnate leaves, and compound' umbels of yellow flowers. Involucre and involucels commonly none. Calyx-teeth obsolete. Stylopodium depressed. Fruit oval, glabrous, much flattened dorsally; dorsal and intermediate ribs filiform, the lateral winged, those of the two carpels contiguous and forming a broad margin to the fruit; oil-tubes solitary in the intervals and 2-4 on the commissural side. Seed very flat. [Latin pastus, food.]
About 7 species, natives of Europe and Asia, the following typica
Biennial or rarely annual, glabrous, or somewhat downy-pubescent, 2°-5° high, the root long, conic, fleshy, the stem grooved. Lower and basal leaves petioled, pinnate, often 1 1/2° long, the segments rather thin, ovate or oval, obtuse, sessile, lobed or incised and sharply dentate, 1' - 3' long; upper leaves generally much reduced; umbels several or numerous, 2'-6' broad, 7-15-rayed, the rays slender, 1/2-2' long; pedicels very slender, 3"-6" long in fruit; fruit broadly oval, 2 1/2-3 1/2 long, 2"-3" broad, the dorsal and intermediate ribs not prominent but the oil-tubes conspicuous.