Oak trees belong to the Family Fagaceae which also include beeches, chestnuts, and tanbark oaks (Lithcarpus) which are not really oaks because their acorn husks resemble that of chestnuts rather than true oaks.

With over 600 species, there is a wide variation of form within the genus Quercus. When one says “oak” one is usually picturing a tree but, there are also many species of oak shrubs as well.  Trees have a single trunk with lateral branch growth whereas shrubs are multi-trunked.  Most oaks are evergreen* but some are winter or drought deciduous ** if need be (clever trees).

Whatever their habit (shape), all oaks share basic characteristics. Oaks have male and female organs on the same tree in the form of catkins. The resulting single nuts--that we call acorns—are partially covered by a scaled cap. All oaks will produce acorns but it may take many, many years—even decades—before this happens.  But once started, oaks will fruit until its death.  However, some years can be barren.

The leaves are usually deeply lobed although there are species such as Q. agrifolia that are not.

Most oaks prefer deep, rich, alluvial soil that is well drained. But there are a few such as Q. alba that like clay.

Being highly resistant to pests, oaks can live a long time—two to three hundred years for many species. Some individuals have even survived for six hundred years!


*Will stay green year-long  i.e. no leaf drop.

**If winter conditions are harsh or there is a severe drought some oaks will drop its leaves.



John Kelly, edt., The Hillside Gardener’s Guide To Trees and Shrubs (Pleasantville, NY/Montreal, CA: Reader’s Digest, 1995),  479.    

Sean Hogan, cns., Flora—A Gardener’s Encyclopedia (Oakland, CA: Timber Press, 2003), 1122.