aroma clingstone color colour cultivars delicate drupes edible firm food fresh fruit healthy jam juicy kernel nectarines nutritious peaches pit Prunus prunus-persica-var.-nectarine red ripe Rosaceae seed skin smooth smooth skin stone stone-fruit sweet tasty tree-fruit variety whole prunus persica var. nectarine stone fruit tree fruit whitish flesh fruit-tree green growing growth leaves prunus-persica-nectarine ripening Unripe