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..
Thalspi arvense L. Sp. Pl. 646. 1753.
Annual, erect, glabrous, 6'-18' high, simple or branching above. Basal leaves petioled, oblanceolate, early deciduous; stem-leaves oblong or lanceolate, sparingly dentate, the upper clasping the stem by an auricled base, the lower merely sessile; flowers white, about 1" long, 1/2" broad; pedicels spreading or curved upward, slender, 5"-9" long in fruit; pods nearly orbicular when ripe, 4' -6" broad, very flat, broadly winged all around, notched at the apex, in long racemes; style minute, or none; seeds rugose, about 6 in each cell.
Thlaspi perfoliatum L. Sp. Pl. 646. 1753.
Annual, glabrous, branched at the base, stems commonly simple, slender, ascending or erect, 3'-7' tall. Basal leaves ovate or suborbicular, often petioled; stem-leaves oblong or oblong-lanceolate, sessile, auricled at the base and clasping the stem, 1/2'-1' long, 3"-6" wide, obtuse or acute at the apex; pedicels filiform, spreading; silicle obovate-orbicular, 2"-3" broad, rather narrowly winged, broadly notched at the summit; style short but manifest; seeds usually 4 in each cell.
Hamilton, Ontario, and Geneva, New York. Advcntive from Europe. May-Aug.