There are two broad types of Endive, curly and broad-leafed.
Both curly and broad-leafed versions belong to the same family as Aster flowers. The seeds for both types of Endive are very small; it takes about 350,000 to 450,000 to make up a pound (450g.)
The leaves of both varieties have a mild, pleasing bitterness, unless left in the ground too long: if they become overmature, they get tough and unpleasantly bitter.
Endive doesn’t “bolt” as easily in summer heat as does its sweeter salad friend, lettuce.
Belgian Endive is not actually endive at all; it is chicory.
Good both used fresh in salads, and braised.
Endive was used by the Egyptians, Romans and Greeks, both raw and cooked. (The Romans acquired it in the first century AD). Some say it is native to India; others say it is native to the Mediterranean.
Endive was being grown in Northern Europe by the 1200s. It was brought to America by colonists.
Literature & Lore
Sometimes in North America, the curly-leaved variety is called “chicory”, in order to help consumers not confuse curly-leaved endive with broad-leaf endive. Given that there’s already a salad green called “chicory”, it’s uncertain how that is going to help any overall confusion.