Original: The Key lime ( Citrus aurantifolia ) is a citrus species with a globose fruit , 2.5-5 cm in diameter ( 1-2 in ) , that is yellow when ripe but usually picked green commercially .
Simplified: The Key lime is a citrus fruit . Its fruit is 2.5-5 cm in diameter ( 1-2 in ) . The fruit is yellow when ripe but usually it is picked green .