Although this chart is illustrative of the form of cotyledons i.e. the embryonic leaf in seed-bearing plants, one or more of which are the first leaves to appear from a germinating seed, most of the terms are also used to describe leave shapes in mature plants.
The word cotyledon originates with the Greek word for cup: kotulē.
From Germination of Australian Native Plant Seed, Editor P.J. Langkamp, published 1987.