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Armoracia is the scientific name for the genus that includes most species of horseradish. This genus is a subset of the plant family Brassicaceae, more commonly called the mustard family, which also includes plants such as cabbages, turnips, radishes, and wasabi. One of the most common species of the genus is Armoracia rustica, or variegated horseradish, which is a perennial flowering plant widely grown for its culinary uses. Both the roots and leaves of the plant are edible, with the roots often being grated or cut and used as a condiment for meat or fish. The leaves of Armoracia rustica are not eaten as often as the roots.
Although it is likely that the genus is indigenous to southeastern Europe or western Asia, most species of Armoracia can thrive in a wide variety of different climates. While some species have small, white flowers, these flowers are sterile and do not produce any seed, so most horseradish plants must be propagated using a method called root division. This involves taking a cutting from the plant's roots and planting the cutting, which will eventually develop into a new, separate plant.
Armoracia rustica, the variegated horseradish, is a perennial plant that usually achieves a height of about three feet (one meter), but may grow to be as tall as five feet (one and a half meters). It has flat, broad leaves that somewhat resemble the leaves of a cabbage or other leafy vegetable. As its name suggests, these leaves are not a solid color and are usually a bright green mottled with white or off-white spots. These white spots fade when the plant is physically disturbed, only to reappear when it is calm again. Armoracia rustica also has tiny white flowers on long stalks, which bloom between the end of spring and the beginning of summer.
While its variegated leaves are rather attractive, the primary purpose of growing Armoracia rustica is for its roots. When the roots are uncut, they have no smell at all, but cutting or grating them releases a pungent oil called allyl isothiocyanate, or mustard oil. Along with this strong aroma, the roots have a sharp, spicy taste, which is why they are frequently used as a condiment. When left out in open air, the cut roots begin to turn from white to brown and take on a bitter taste, so they are often grated and preserved in vinegar. This preparation of horseradish is popular in many parts of the world, and is used to add flavor to roasts, steaks, seafood dishes, sandwiches, and soups, or dyed green and served as an inexpensive alternative to Japanese wasabi alongside sushi dishes.
There are also traditional medicinal uses for plants from this genus. Horseradish root is a diuretic, meaning that it heightens the urge to urinate, so it may be used to treat urinary tract infections. Since the powerful aroma of the root also stimulates and irritates the sinus cavities, it may also be used to relieve sinus congestion.