One population from San Juan County, Utah, with larger fruit but otherwise not differing from typical Quercus gambelii , has been recognized as Q . gambelii var. bonina Welsh. Unless other characters are found to support this segregation, the plants are best not treated as a formal taxon, particularly considering the extensive variation and hybridization associated with Q . gambelii throughout its range.
Numerous putative hybrid swarms occur throughout the range of Quercus gambelii that involve a number of suspected parental species. Most of these populations have, at one time or another, been referred to Quercus undulata Torrey. The putative hybrids have serrate or shallowly lobed leaves and considerable variation in habit, leaf pubescence, and acorn morphology. J. M. Tucker (1961, 1969, 1971) and J. M. Tucker et al. (1961) have identified the major components of the Q . undulata complex as Q . turbinella (western Utah and northwestern Arizona, and central Colorado), Q . grisea (New Mexico and southern Colorado), Q . havardii (southeastern Utah and northwestern Arizona), Q . mohriana (northeastern and southern New Mexico), Q . arizonica (central Arizona), and Q . muhlenbergii (eastern and central New Mexico). Quercus macrocarpa has been implicated as a parent of variable populations in New Mexico (J. M. Tucker and J. R. Maze 1966). Because of the complex variability in these populations, no effort has been made to treat them separately here; indeed, it would be impossible to produce usable keys if these were included as formal taxa.
Hybrids derived from Quercus gambelii and an evergreen species are often semideciduous, retaining a variable portion of green or brownish leaves over the winter.
Quercus gambelii was used medicinally by the Navaho-Ramah to alleviate postpartum pain, as a cathartic, as a ceremonial emetic, and as a life medicine (D. E. Moerman 1986).