Also known as Belgian or French endive - witloof (white leaf) is the blanched shoots of a chicory root.
Made up of a small head of cream-coloured bitter leaves.
Green pigment in the outer edge of the leaves.
Usually grown indoors away from sunlight to preserve flavour and colouring.

Look for crisp, compact heads that are creamy white with the leaf tops just barely green or red (depending on variety). 
Avoid heads with leaves that have begun to splay outward from the tight core.