where are they commonly cultivated and used?
It is perennial in hardiness zones 2–9.
Horseradish
Horseradish is perennial in hardiness zones 2–9 and can be grown as an annual in other zones, although not as successfully as in zones with both a long growing season and winter temperatures cold enough to ensure plant dormancy. 
when did radishes become a food source for humans They were domesticated in Asia prior to Roman times. how are they consumed? They are mostly eaten raw as a crunchy salad vegetable with bite. are there other varieties? Yes, they differ based on the  seasons when they are grown and a variety of shapes, lengths, colors, and sizes, such as red, pink, white, gray-black, or yellow radishes, with round or elongated roots that can grow longer than a parsnip. what are parsnips? It is a root vegetable closely related to carrot and parsley; all belong to the family Apiaceae. what chemical compound give the first mentioned root vegetable its sharp taste? Glucosinolate, myrosinase, and isothiocyanate is the first mentioned compound found in any other plants? Yes, in mustard, cabbage, and horseradish. is the vegetable mentioned in the beginning and the third mentioned vegetable in the answer above are the same? No, but belongs to the same family of Brassicaceae
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Horseradish [SEP] Cultivation
Horseradish is perennial in hardiness zones 2–9 and can be grown as an annual in other zones, although not as successfully as in zones with both a long growing season and winter temperatures cold enough to ensure plant dormancy. After the first frost in autumn kills the leaves, the root is dug and divided. The main root is harvested and one or more large offshoots of the main root are replanted to produce next year's crop. Horseradish left undisturbed in the garden spreads via underground shoots and can become invasive. Older roots left in the ground become woody, after which they are no longer culinarily useful, although older plants can be dug and re-divided to start new plants.