Short answers, pulled from the story.
Kohlrabi is a biennial vegetable, a low, stout cultivar of wild cabbage with the scientific name Brassica oleracea, Gongylodes Group. Its taste and texture resemble a broccoli stem or cabbage heart, but milder and sweeter, and the young stem can be as crisp and juicy as an apple.
Kohlrabi is called German turnip and turnip cabbage because its swollen stem resembles a turnip, and its name joins the German Kohl, meaning cabbage, with Rube, meaning turnip. Despite these names it is not the same species as turnip or rutabaga, though both belong to the genus Brassica.
The first European written record of kohlrabi was made by the botanist Mattioli in 1554, who noted that it had come lately into Italy. By the end of the 16th century it was being grown in Austria, Germany, England, Italy, Spain, Tripoli, and parts of the eastern Mediterranean.
Common kohlrabi varieties include White Vienna, Purple Vienna, Grand Duke, Gigante (also known as Superschmelz), Purple Danube, and White Danube. The purple coloring is only superficial, since the edible parts of all types are pale yellow.
Kohlrabi is eaten raw or cooked, often sliced thin in salad or slaw, while its leaves are used like collard greens and kale. It is central to Kashmiri cuisine as Monji, served as an appetizer with salt and lemon in Cyprus, and used in Vietnamese dishes such as nem ran, stir fry, and canh.
Raw kohlrabi is 91 percent water, 6 percent carbohydrates, 2 percent protein, and contains negligible fat. A 100 gram amount supplies 27 calories and is a rich source of vitamin C at 65 percent of the Daily Value, with moderate copper and potassium.