Texas Live Oak

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.

Populations of live oak on deep sands in south Texas differ from typical Quercus fusiformis in having broader, more rounded leaves, often with the secondary veins somewhat impressed abaxially, and relatively blunt, barrel-shaped acorns. These characteristics suggest introgresion from the Mexican-Central American species Q . oleoides Schlechtendal & Chamisso, which in its typical form reaches north only as far as southern Tamaulipas, Mexico. The name Q . oleoides var. quaterna C. H. Muller has been applied to what is apparently a shrub form of one of these Q . fusiformis × Q . oleoides hybrids.

Trees, sometimes shrubs , subevergreen, trees to 25 m, shrubs often forming large clonal stands. Bark dark brown or black, scaly. Twigs light gray, 1.5-3 mm diam., tomentulose, tomentulum often persistent in age. Buds reddish or dark brown, subglobose or ovate, 1.5-3 mm; scale margins glabrous or puberulent. Leaves: petiole 2-8(-12) mm. Leaf blade oblong-elliptic to narrowly ovate or lanceolate, sometimes obovate, ± planar, (10-)35-90(-150) × (15-)20-40(-85) mm, base rounded to truncate or cordate, rarely cuneate, margins minutely revolute or flat, entire or irregularly 1-3 toothed on each side, teeth mucronate (rarely spinose in suckers or juveniles), secondary veins obscure, 8-10 on each side, apex obtuse-rounded or acute; surfaces abaxially whitish or glaucous, densely covered with minute, appressed, fused-stellate hairs, light green and glabrate in shade leaves, adaxially dark or light green, glossy, glabrous or with minute, scattered, stellate hairs. Acorns 1-3, on peduncle 3-30 mm; cup funnel-shaped, hemispheric, or deeply goblet-shaped, 8-15 mm deep × 6-12(-15) mm wide, base often constricted, scales whitish or grayish, thickened basally, keeled, acute-attenuate, tomentulose, tips reddish, glabrous or puberulent; nut dark brown, often with light brown longitudinal stripes, subfusiform and acute to narrowly barrel-shaped, rarely distally rounded, (17-)20-30(-33) × 8-15 mm, glabrous. Cotyledons connate.

Okla., Tex.; Mexico (Coahuila, Nuevo León, and Tamaulipas).

Flowering spring.

Hills, grasslands, scrublands, open woodlands, oak-juniper woodland, and margins of thorn scrub, often on limestone or deep calcareous loams, sometimes on granular sand or gravel; 0-1200m.

Quercus virginiana Miller var. fusiformis (Small) Sargent

Quercus fusiformis (also often referred to as Q. virginiana var. fusiformis), commonly known as escarpment live oak, plateau live oak, plateau oak, or Texas live oak, is an evergreen or nearly evergreen tree. Its native range includes the Quartz Mountains and Wichita Mountains in southwestern Oklahoma, through Texas, to the Mexican states of Coahuila, Tamaulipas, and Nuevo León.

Quercus fusiformis is an evergreen tree in the southern live oaks section of the genus Quercus (section Virentes). It is distinguished from Quercus virginiana (southern live oak) most easily by the acorns, which are slightly larger and with a more pointed apex. It is also a smaller tree, not exceeding 1 metre (40 inches) in trunk diameter – compared to 2.5 m (75 in) in diameter in southern live oak – with more erect branching and a less wide crown. Like Q. virginiana, its magnificent, stately form and unparalleled longevity has endeared it to generations of residents throughout its native range. Its low hanging branches are a favorite for local children to climb and play in.

Escarpment live oak is typically found on dry sites, unlike southern live oak, which prefers moister conditions. The tree, especially the Quartz Mountains variety, is generally accepted to be the hardiest evergreen oak, able to withstand very cold winters with minimal leaf burn in areas as cold as USDA zone 6a. For this reason the tree has become popular within the landscape industry for its beauty, ability to endure urban conditions, and general hardiness. It is prevalently used for these purposes in Texas and southern Oklahoma but use is becoming more widespread in the Western US.

The largest recorded individual tree of Q. fusiformis in the state of Texas is found in Bosque County (not to be confused with the "Election Oak" or Bosque County Oak). It has a circumference of 870 centimetres (342 in), which is actually larger than the largest recorded Q. virginiana in the state, listed at 860 cm (338 in).