The seeds oft he Carob tree Ceratonia siliqua have made a distinguished career: they are held as the basis for karat, the measure of the purity of gold.
The ancient Romans used a small weight unit that was called 'siliqua.' It corresponded to the weight of one seed of the Carob tree, which is 0.19 grams. Thus, a siliqua had about the same weight as a karat, whose weight was standardized to 0.2 grams in 1907.