Eucalyptus is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with other genera in the tribe Eucalypteae, they are commonly known as eucalypts or gum trees. Plants in the genus Eucalyptus have bark that is either smooth, fibrous, hard or stringy, leaves with oil glands, and sepals and petals that are fused to form a "cap" or operculum over the stamens. The fruit is a woody capsule commonly referred to as a "gum nut". Sometimes gum trees contain geocaches.