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| Oak (Quercus) | |
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| Foliage and acorns of Quercus robur | |
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| Genus: | Quercus |
The oak tree is a tree or shrub in the genus Quercus. There are about 500 living species. They are divided into subgenera. The common name "oak" may also appear in the names of species in related genera, such as Lithocarpus.
Oaks have spirally arranged leaves, with rounded edges in many species; some have leaves with jagged edges or entire leaves with smooth margins. Many deciduous species do not drop dead leaves until the next Spring. In Spring, a single oak tree produces both male flowers (as catkins) and small female flowers. The fruit is a nut called an acorn, carried in a cup-like structure. Each acorn has one seed (rarely two or three) and takes 6–18 months to mature, depending on species. The so-called "live oaks" are evergreen. They are not a taxonomic group, just a life style which occurs in the genus.
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