walnut

A walnut is the edible seed of any tree of the genus Juglans (family Juglandaceae), particularly the Persian or English walnut, Juglans regia. The fruits of trees in the family Juglandaceae are often confused with drupes. Still, they are accessory fruit because the outer covering of the fruit is technically an involucre and thus not morphologically part of the carpel; this means it cannot be a drupe but is instead a drupe-like nut. After full ripening, the shell is discarded, and the kernel is eaten. Nuts of the eastern black walnut (Juglans nigra) and butternuts (Juglans cinerea) are less commonly consumed. Characteristics Walnuts are the round, single-seed stone fruits of the walnut tree. They are commonly used for food. They ripen between September and November in the northern hemisphere. The brown, wrinkly walnut shell is enclosed in a husk. Shells of walnuts available in commerce usually have two segments (but three or four-segment shells can also form). During the ripening process, the husk becomes brittle and the shell hard. The shell encloses the kernel or meat, which is usually in two halves separated by a membranous partition. The seed kernels – commonly available as shelled walnuts – are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen, preventing rancidity. Walnut trees are late to grow leaves, typically not leafing until more than halfway through the spring.