An oak is a tree or shrub in the genus Quercus (Latin ”oak tree”), having 600 extant species. “Oak” may also appear in the names of species in related genera, notably Lithocarpus. The genus is native to theNorthern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropicallatitudes in Asia and the Americas.
Oaks have spirally arranged leaves, with lobed margins in many species; some have serrated leaves or entire leaves with smooth margins. Many deciduous species are marcescent, not dropping dead leaves until spring. Theflowers are catkins, produced in spring. The fruit is a nut called an acorn, borne in a cup-like structure known as acupule; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on species. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.
