Roots fusiform or cylindrical, fleshy or woody. Stems 5-12 (-20) dm. Basal leaves: petiole to 60 cm (broadly expanded basally); blade broadly oblong, oblong-lanceolate, or ovate, (10-)20-45(-60) cm × (30-)50-120(-170) mm, margins usually coarsely crenate, rarely pinnatifid. Cauline leaves: proximal shortly petiolate, blade oblong to linear-oblong (lobed), smaller than basal, margins pinnatifid or pinnatisect; distal sessile or shortly petiolate, blade linear to linear-lanceolate, base cuneate or attenuate, margins usually serrate or crenate, rarely entire. Racemes to 40 cm. Fruiting pedicels ascending, 8-20 mm. Flowers: sepals 2-4 mm; petals obovate or oblanceolate, 5-7 (-8) mm, claw to 1.5 mm; filaments 1-2.5 mm; anthers 0.5-0.8 mm. Fruits (rarely produced), 4-6 mm; style obsolete or to 0.5 mm; stigma well-developed. Seeds compressed (often not produced, rarely to 4 per locule). 2n = 32. Flowering Mar-Jul. Fields, moist stream banks, roadsides, ditches, disturbed sites, open woods, along railroads, shallow ponds, marshes, waste places; 0-1100 m; introduced; B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask.; Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Europe; Asia; introduced also nearly worldwide. Armoracia rusticana has been widely cultivated for about 2000 years for its fleshy roots that are grated to produce the pungent horseradish sauce. The plant is also a noxious weed that is very difficult to eradicate, even tiny root fragments are capable of regenerating new plants.
Perennial herb to 1 m tall Stem: upright. Flowers: in branched clusters, pink or pinkish purple, 6 - 8 mm long. Petals four, tip rounded. Stamens six. Fruit: a pod, ascending, to 6 mm long, on a short stalk, egg-shaped, slightly round in cross-section, two-chambered. Lower leaves: long-stalked, 10 - 30 cm long, oblong, base heart-shaped, toothed. Upper leaves: alternate, stalkless or short-stalked, smaller than lower leaves, lance-shaped, toothed.
Similar species: Armoracia rusticana is the only representative of the genus Armoracia in the Chicago Region. Its height and large, oblong basal leaves are distinctive.
Flowering: May to early June
Habitat and ecology: Introduced from Europe. Often cultivated in home gardens. It readily grows from a root piece, and therefore escapes from cultivation as a result of earth-moving operations. Often found in moist soil, usually along ditches, roadsides, and stream banks. Has also been found growing along railroads.
Occurence in the Chicago region: non-native
Notes: The condiment Horseradish is made from the root.
Etymology: Armoracia is an old name for the genus. Rusticana means rustic (of the countryside).
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
Much planted and used as a condiment. It has sparingly escaped from cultivation to ditches and banks of the smaller streams throughout the state. I once found it on the bank of a pond in a clearing. I have never seen it mature seed.
Indiana Coefficient of Conservatism: C = null, non-native
Sep ascending, elliptic to obovate; pet white, obovate, gradually narrowed to the claw; short stamens subtended by a U - shaped gland; long stamens subtended by a small conic gland; anthers linear-oblong; ovary ovoid to ellipsoid; ovules numerous; style slender, stigma large, capitate; frs inflated, obovoid or ellipsoid, tipped with the slender style and conspicuous stigma; valves with an inconspicuous midnerve, otherwise nerveless; glabrous herbs. 4, Europe to Siberia.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.