This is widespread across most of eastern North America, but rare to absent on the southeastern Coastal Plain. In Ky. there are occasional hybrids with several other species (at least shumardii and imbricaria). Distinctive features are as follows ( FNA 3, J, W): unusually shallow acorn cups (but see also shumardii); relatively large leaves with shallow, forward-pointing lobes and little to no pubescence; upper leaf surfaces dull (versus lustrous); twigs and buds reddish brown (versus grayish or reddish). Q. rubra also has relatively efficient "self-pruning" of old or dead branchlets, leading to less scraggly crown shapes. There are no wild records from Ky. of the northern var. ambigua (Gray) Fern. (= var. borealis (Michx. f.) Farw.), which appears to be generally distinct (FNA 3; Ladd & Thomas 2015). Var. ambigua is generally reporterd to have deeper cups around acorns (about a third covered versus a quarter), leaves with deeper sinuses (up to 1/3 versus 1/4), more glaucous below, and paler smoother bark (F, W). Ladd & Thomas added: in more acidic soils and at higher elevations, trunk often straighter (versus subtly sinuous), with grayer bark trunk (versus contrasting blackish and whitish strips), and pubescent tips on buds (versus glabrous). And there is evidence of different flavonoid chemistry (McDougal & Parks 1976). Many planted trees in Ky. with probable northern origins appear to be var. ambigua, especially in urban areas, and they probably contribute significantly to local gene-pools. These trees can easily be confused with some forms of shumardii or with putative rubra-shumardii intergrades. Further refinement is needed in keys to these taxa. Q. rubra is generally considered to be the most shade tolerant red oak, but it still appears to depend on gaps for regeneration. It can also be relatively palatable to deer or other generalist herbivores; and white oaks tend to be less palatable than reds (Atwood 1941). Old fields on mesic slopes within the wooded hills of Ky. tend to be dominated by Liriodendron instead, which has more mass-dispersal through winged seeds, and tends to be less palatable than Q. rubra.