The archetypal oak grows large and spreads wide, with muscular, near-horizontal lower branches that seem to defy gravity. But the group’s 500 species, all native to the Northern Hemisphere, also include upright, pyramidal, and shrubby oaks; in fact, “chaparral” comes from chaparra—Spanish for a dwarf evergreen shrub oak. Oak leaves can be deciduous or evergreen (the latter are called live oaks); lobed, toothed, or smooth edged; but they’re always arranged in an alternate pattern along stems. Some have terrific fall color. All oaks produce inconspicuous flowers followed by acorns, whose single nuts have cuplike caps covered with closely set scales. Some kinds of acorns are edible and sweet, while others are bitter and unpalatable.
Oaks come in two broad categories: white oaks have acorns that mature during the season in which they are produced, and often have leaves with rounded lobes; red and black oaks have acorns that take two seasons to mature, and often have leaves with pointed lobes. Each group can hybridize only within itself.Quercus suber
This evergreen grows to 30–60 ft. tall and wide. Trunk and main limbs are covered with handsome, thick, corky bark (the cork of commerce). Toothed, 3-in., oval leaves are shiny dark green above, gray beneath. Egg-shaped acorns with a short point are 3/4–1/2 in. long, covered by one-third to one-half in a bowl-shaped cap. Good garden shade tree; light-textured foliage contrasts interestingly with the massive, fissured trunk. Needs good drainage. Fairly tolerant of various soils, but foliage may turn yellow in highly alkaline conditions. One of the best oaks for desert areas. Value as a street or park tree diminishes when children find out how easy it is to carve its bark.
Zebra rush forms an upright, grassy clump to 2–4 ft. tall and wide. Hollow, leafless, dark green...
This evergreen grows to 30–60 ft. tall and wide. Trunk and main limbs are covered with handsome,...
This is the most commonly grown species. In bloom it reaches 4–5 ft. high. The spineless leaves ...