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Monday - March 17, 2008

From: Austin, TX
Region: Southwest
Topic: Trees
Title: Difference between liveoaks (Quercus fusiformis and Q. virginiana)
Answered by: Nan Hampton

QUESTION:

I am a little confused on the identification differences between Quercus fusiformis and Quercus virginiana. How can you properly identify between the two?

ANSWER:

You are not the only person confused about the differences between Quercus fusiformis (plateau oak or escarpment live oak) and Quercus virginiana (live oak). As Benny Simpson in Field Guide to Texas Trees says about Q. virginiana:

"It is easily confused with Escarpment Live Oak and other members of this series that occur in the southeastern United States."

Habitat is one of the best ways to distinguish between the two. Quercus virginiana is found along the coastal areas of the southeastern United States. According to Turner's Atlas of the Vascular Plants of Texas, Vol. 1, in Texas it occurs only as far west as eastern Williamson County and eastern Bell County. The majority of the occurrences are east and south of Bell County, mostly clustered along the Gulf Coast. Quercus fusiformis, on the other hand, occurs mainly west of the line of counties including McLellan, Bell, Williamson, Travis, Hays, Comal and Bexar—generally, the Edwards Plateau. There is also a grouping in the southern tip of Texas in the South Texas Plains. Additionally, there is an eastern line of counties (including Goliad, DeWitt, Lavaca, Colorado, Fayette, Bastrop, Washington and Brazos) where Q. fusiformis and Q. virginiana overlap. This overlap area is where the confusion abounds. Robert Vines in Trees of Central Texas says about Q. fusiformis:

"Although it appears distinct in the western part of its distribution (beyond the Edwards Plateau area and into Mexico), on its eastern range it seems to pass into Q. virginiana with many intermediary variants."

Benny Simpson says this about Q. fusiformis:

"Escarpment Live Oak grows in mottes, attaining heights of 50 feet, on almost any alkaline to slightly acid, well-drained soil. It is rather rare on the the true Blackland Prairies, possibly because of the poor internal drainage of those soils, but it does occur in the West Cross Timbers and Grand Prairie, west and north of the Balcones Escarpment on the Edwards Plateau, and, to a lesser degree, east of the Balcones Fault Line on the Blackland Prairies. It grows in hybrid swarms of Quercus virginiana x Q. fusiformis from the Balcones Escarptment to the coastal area and then eastward to the Brazos River, where, on the east side, more or less pure forms of Q. virginiana are encountered."

One distinction between the two is in the shape of the acorn. In Q. fusiformis, the acorns are, according to Vines:

"Borne on peduncles 3/4-2 1/3 in. long, solitary or several together. The cups much constricted basally and flaring upward. Acorn elongate, fusiform or subfusiform, brown, shiny."

Vines' description of the acorns of Q. virginiana is:

"Acorn on peduncles 1/4-4 in. long, in clusters of 3-5; nut ellipsoid-obovoid, brownish black, shiny, 1/3-1/2 in. long; enclosed about one-half its length in the cup; cup turbinate, light reddish brown, hoary-tomentose, scales of cup ovate, acute, thin appressed."

Vines gives the height for Q. virginiana as 60 ft. and for Q. fusiformis as 36 ft. tall.

There is a dichotomous key in Delena Tull's and George Miller's Lone Star Guide to Wildflowers, Trees, and Shrubs of Texas that can guide you through the various features of the two species.

You can also read the description of Q. virginiana and Q. fusisormis from Flora of North America. You will see, as you read the descriptions, that many of the descriptors are very similar, if not identical.

Read, especially, under the description of Q. fusifomis:

"The difficulty in distinguishing Texas populations of Quercus fusiformis from Q . virginiana is reflected in a variety of taxonomic treatments, including reducing Q . fusiformis to varietal rank under Q . virginiana . The latter disposition is problematic, however, because Q . fusiformis in northeastern Mexico is amply distinct from Q . virginiana and appears to be more closely related to Q . brandegei Goldmann, an endemic of Baja California, Mexico. Thus, here we assume that the intergradation of Q . virginiana and Q . fusiformis is a result of secondary contact, and is not primary clinal variation. Under this interpretation, Q . virginiana in typical form extends into Texas only as far west as the Brazos River drainage along the coast from there to the escarpment of the Edwards Plateau; most populations elsewhere are either intermediate between the two species or show greater affinity with Q . fusiformis . On the Edwards Plateau, the live oak populations are small trees forming rhizomatous copses (shinneries) and having mostly acute acorns."

 

 

 

 

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Bibliography

Atlas of the Vascular Plants of Texas (2003) Turner, B. L.; H. Nichols; G. Denny; O. Doron

Field Guide to Texas Trees (1999) Simpson, B.J.

Lone Star Field Guide to Wildflowers, Trees, and Shrubs of Texas, Revised Edition (2003) Tull, D. & G.O. Miller

Trees of Central Texas (1984) Vines, Robert A.

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