Armoracia rusticana is a perennial herb to 1 m tall, erect, from a thick, woody, vertical tap root.
Leaves alternate, basal leaves to 30 cm long, base lobed, margin round-toothed (crenate), long-stalked, stem leaves narrow, smaller, short-stalked to stalkless, the lowest sometimes pinnately divided.
Flowers white, 4-parted, petals to 0.8 cm; May-July.
Fruit dry, hollow capsule, rounded to 0.6 cm, with elongate old stigma at tip, seeds rarely mature.
Wetland status: UPL.
Frequency in NYC: Very infrequent.
Origin: Europe, w. Asia.
Habitat: Escaped from cultivation into moist, open soil.
Notes: Leaves and roots contain mustard oil, a mixture of isothiocynates, pungent, irritating nitrogen-sulfur compounds of the form, CHx-N=C=S, poisonous to livestock (Kingsbury 1964).