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..
Annual or perennial herbs, stellate-pubescent or canescent, the leaves mostly narrow and entire, and the flowers white in terminal racemes. Petals 2-cleft. Filaments 2-toothed at the base. Silicles oblong or subglobose, somewhat compressed. Seeds several in each cell, winged. Cotyledons accumbent. [In honor of C. G. Bertero, a botanist of Piedmont, 1739-1831.]
About 5 species, natives of Europe and Asia, the following typical.
Alyssum incanum L. Sp. Pl. 650. 1753. Berteroa incana DC. Syst. 2: 291. 1821.
Erect or ascending, 1°-2° high, hoary-pubescent, branching above. Leaves lanceolate or oblong, 1/2'-1 1/2' long, obtuse, entire or slightly undulate, the lower narrowed into a petiole; flowers white, 1"-1 1/2" broad; pedicels ascending, 2"-3" long in fruit; pod canescent, swollen, oblong, 3"-4" long and about half as broad; style 1"-1 1/2" long; stigma minute.
Berteroa mutábilis (Vent.) DC, also native of Europe, has a more compressed, sparingly pubescent and slightly larger pod; it is recorded as adventive in Massachusetts.