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
Horseradish
Horseradish ("Armoracia rusticana", syn. "Cochlearia armoracia") is a perennial plant of the family Brassicaceae (which also includes mustard, wasabi, broccoli, cabbage, and radish).
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.
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Horseradish [SEP] Introduction
Horseradish ("Armoracia rusticana", syn. "Cochlearia armoracia") is a perennial plant of the family Brassicaceae (which also includes mustard, wasabi, broccoli, cabbage, and radish). It is a root vegetable, cultivated and used worldwide as a spice and as a condiment. The species is probably native to southeastern Europe and western Asia.