Quercus engelmannii aka Engelmann's Oak

Quercus engelmannii is known as Engelmann oak or mesa oak. It belongs to the beech family, Fagaceae. Its native range runs from southern California into northern Baja California. It grows on low hills and dry, rolling mesas. These sites have well-drained soils. This oak keeps its leaves but can shed them during drought. Its name honors George Engelmann, a physician and botanist.

Garden references give heights of 15–50 feet [4.6–15.2 metres]. Plants For A Future gives a height of 33 feet [10 metres]. The tree has a short trunk and wide, spreading limbs. The trunk and large limbs can twist as they grow. Trees in open sites form a rounded crown. Their foliage can reach the ground. Gray bark has small, scaly ridges and shallow grooves. Brown twigs bear fine hairs, as do the reddish-brown end buds.

The leaves grow in an alternate pattern along the twigs. Each leaf is simple, stiff, and leathery. Leaves range from oblong to oval, with rounded ends. Their edges may be smooth, wavy, or lightly toothed. The upper side looks dull blue-green or gray-green. The lower side is paler and hairy when young. Those hairs can disappear as leaves age. Each tree bears both male and female flowers. Yellow-green male flowers hang in narrow catkins. Small female flowers sit near the leaves. Wind carries the pollen, and Plants For A Future lists flowering in May. Acorns ripen in autumn during their first year. Their thick, bumpy cups cover roughly one-third to half the nut.

Oregon State recommends sun and monthly deep watering during dry weather. Plants For A Future also lists partial shade and moist soil. It lists loam and clay, with mildly acid to mildly alkaline pH. Oregon State places the tree in USDA zone 8. Plants For A Future gives zones 8–11 and calls it frost tender. It also reports a moderate growth rate. Landscape uses include a specimen tree or street tree. Its broad crown also suits a woodland canopy.

Plants For A Future lists cooked seeds as edible after tannin removal. The bitter tannins require thorough leaching before food use. Ground seeds can thicken stews or be mixed into bread flour. That source reports no known hazards, rather than confirmed safety. It lists the hard, heavy wood as fuel. Insect larvae can cause galls, which provide tannin and dye. The supplied sources name no specific diseases.