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..
Erect, or rarely diffuse, glabrous or pubescent herbs, with pinnatifid lobed or entire leaves and racemose white or whitish flowers. Pubescence,' when present, of simple hairs. Stamens often fewer than 6. Petals short, sometimes none. Silicles orbicular to oblong or obovate, flattened contrary to the partition, mostly emarginate, winged or wingless; valves keeled, dehiscent. Seeds solitary in each cell, pendulous, flattened; cotyledons incumbent or rarely accumbent. [Greek, a little scale, from the flat scale-like pods.]
About 65 species, widely distributed. In addition to the following, about 16 others occur in western North America. Called indifferently Cress, Pepperwort or Pepper-grass. Type species: Lepidium latifolium L.
Stem-leaves clasping by an auriculate base.
Pods broadly ovate, winged; annual or biennial.
Pods wingless, broader than long; perennial.
Stem-leaves petioled or sessile, not clasping.
Pods and seeds entirely wingless; petals none; cotyledons incumbent.
Pods slightly winged above, orbicular or oval, about I" broad; petals present or none.
Cotyledons accumbent; petals generally present.
Cotyledons incumbent; petals minute or wanting.
Pods oblong, winged all around, longer than wide, about 2" high.
Thlaspi campestre L. Sp. Pl. 646. 1753.
Annual or biennial, erect, 10'-18' high, branching above, hoary-pubescent with scale-like hairs or rarely nearly glabrous. Basal leaves oblong, or spatulate-oblong, entire, or pinnatifid in the lower part, obtuse, petioled, 2-3' long; stem-leaves oblong or lanceolate, entire or slightly dentate, sessile, clasping the stem by an auricled base; flowers white or yellowish; pedicels rather stout, spreading, 2"-4" long in fruit; pods very numerous, forming dense elongated racemes, broadly ovate, slightly curved upward, about equalling their pedicels, or shorter, broadly winged at the apex, rough, notched, tipped with a minute style.
In fields and waste places, New Brunswick and Ontario to Virginia, Kansas, and on the Pacific Coast, a bad weed in the Middle States. Naturalized from Europe. May-July. Yellow seed. Mithridate mustard. Glen-, or poor-man's-pepper. Glen- or crowd-weed. False flax. English pepper-grass.