Download Featured Plant of the Month, August 2012 Mexican White Oak Quercus polymorpha.docx

Featured Plant of the Month, August 2012 Mexican White Oak Monterrey Oak Quercus polymorpha
Location: On the north side of the West Instructional Service Center (ISC).
As the common name implies this species of oak is widespread in Mexico. Populations are seen in the
Sierra Madre Oriental southward into Central America. Not too many years ago the well-known
botanist, B. J. Simpson, author of A Field Guide to Texas Trees, discovered a small grove of this oak
about 18 miles from the Mexican border near Dolan Falls on the Devil’s river in Val Verde County. This is
the only native population reported in Texas to this date. There is not much information in the
literature about this species since it was not recognized as a native until in the 1990s when B. J. Simpson
identified it in Texas.
Oaks are in the Fagaceae (Beech Family). This family has eight genera that include approximately 900
species of trees and a few shrubs. Most of these species occur in the temperate and sub-tropical zones.
Plants of this family are valuable for one or more of these products: timber, tannins, dyes, cork, creosote
and food. The traditional Latin name for the oak genus is Quercus and the specific epithet is from Greek
poly (many) and morph (form). This epithet is used frequently in naming plants that have obvious
variability in some characteristic such as leaf shape as in the case of Quercus polymorpha.
All oaks are in one of either of two possible groups, white oaks or red oaks. White oaks are in the
Subgenus Leucobalanus that includes Bur Oak (Q. macrocarpa), Lacey Oak (Q. laceyi) and Chinkapin Oak
(Q. muehlenbergii) as well as Q. polymorpha. The white oaks are fortunately not as susceptible to the
fungus, Ceratocystis fagacearum that causes oak wilt as the Red Oaks are. The infection has been
reported in some instances in White Oaks, but it is rare. Oak wilt is an infectious disease that destroys
many oak trees in Texas every year.
When Q. polymorpha trees are young they are pyramidal in shape but do grow more rounded with age.
These trees grow in full sun to part shade in a wide range of soil types as long as they are well drained.
They are drought resistant and grow rapidly in a suitable environment. The height of a mature tree can
vary from 30 to 60 feet with a possible spread of 20 to 40 feet. Some older trees have been reported to
have a spread of 60 feet. The leaves are oblong in shape and are 3 to 5 inches in length and have a
leathery texture. The leaves are not deeply lobed as many oak leaves are, but vary in form such as
scalloped or tapered. In the spring the leaves may be gold or bronze to almost red, but when mature
they are a deep green. There is very little, if any, color change in the fall. Depending on where they are
planted and their genetic background Mexican White Oaks are semi-evergreen, tardily deciduous or fully
deciduous. Many growers select for the semi-evergreen characteristic. The Monterrey Oak is the
trademark name used by one grower for this tree.
The pistillate flowers are inconspicuous and the pollen producing staminate flowers are arranged in the
catkin infloresence that is typical of oak trees. These trees cross-pollinate with other oaks species to
form some interesting hybrids. The fruits are acorns that are produced annually. Propagation is by
seeds that can be planted immediately after harvesting; no pre-treatment is required.
The Mexican White Oak is a wonderful plant for landscaping. It does need room to grow because in an
environment that is favorable they do get large. Since the species is less susceptible to oak wilt and
have no insect pests together with their drought resistance they are ideal for wide use in Texas
landscapes. These trees have increased greatly in popularity with growers and landscapers in recent
years.
References:
Baumgardt, John Philip. How to Identify Flowering Plant Families
Nokes, Jill. How to Grow Native Plants of Texas and the Southwest
Stein, J. D. Binon, R. Acciavati . Field Guide to Native Oak Species of Eastern North America.
Internet Search. Key Words: Quercus polymorpha