Leaves of a lily. Abstract arrangement of leaves from the oriental lily (Lilium speciosum). Lilies are monocotyledonous flowering plants. Monocotyledonous plants have narrow leaves with parallel veins, and seeds with only one cotyledon (first leaf of the embryo). Leaves function in making carbohydrates for the plant by photosynthesis. The leaf veins transport water and nutrients to the leaves and carbohydrates away to the rest of the plant.