Flora of the Southeastern United States
2022 Edition

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Key to Quercus, Key C: Leaves with lobes not bristle-tipped (White Oaks)

1 Lower surfaces of mature leaves glabrous.
..2 Leaf lobes with acute apices; sinuses often both broad and "flat-bottomed" (with portions parallel to the midrib); acorn cup covering 2/3 to 3/4 of acorn; [section Quercus; subsection Prinoideae]
..2 Leaf lobes with obtuse apices; sinuses narrow (often notch-like), narrowly to broadly rounded or triangular (lacking portions parallel to the midrib); acorn cup covering < 1/4 to 1/2 of acorn.
....3 Leaves mostly 4-10 (-17) cm long, 2-5 (-9) cm wide, with 1-5 shallow lobes or undulations, extending 1/8 to 1/2 of the way to the midrib; acorn cup flat at the base, covering < ¼ of the acorn; [section Quercus; subsection Stellatae].
......4 Shrubs or small trees to 3(–5) m tall, often forming thickets, trunks multiple from near ground; acorn 7-12 (-15) mm long, 7-10 mm in diameter; [dry limestone hills of OK and TX]
......4 Trees to 20 m tall, trunk usually solitary; acorn 12-15 (-18) mm long, 8-12 (-17) mm in diameter; [moist bottomlands, riparian habitats and calcareous bluffs of SC west to TX]
....3 Leaves mostly 7-20 cm long, 3-10 cm wide, with 3-11 lobes, extending 1/4 to 5/6 of the way to the midrib (if the lobing < ½ of the way to the midrib, then the acorn cup rounded at the base and covering 1/4 to 1/2 of the acorn).
........5 Leaf base deeply cordate; [alien, sometimes planted and persistent]
........5 Leaf base cuneate; [native].
..........6 Leaves with 7-11 lobes (the sinuses usually deep, those of the larger leaves usually about 2/3 to 5/6 of the way to the midrib), 10-20 cm long, 5-10 cm wide; terminal bud rounded or globose; basal scales of acorn cup thickened, the thickening giving the cup a knobby texture; [section Quercus; subsection Albae]
..........6 Leaves with 3-7 lobes (the sinuses usually shallow, those of the larger leaves usually ranging from 1/4 to 1/2 of the way to the midrib), 7-15 cm long, 3-8 cm wide; basal scales of the acorn cup thin, appressed, the cup having a rough but not knobby texture; [section Quercus; subsection Stellatae]
1 Lower surfaces of mature leaves pubescent, the pubescence varying from dense to sparse (sometimes minute and requiring 10× magnification to be readily visible).
............ 7 Lower surfaces of mature leaves whitish to pale green, with a mixture of minute, sessile, stellate hairs with horizontal tips and longer stellate hairs with erect ascending tips; leaves shallowly lobed (if so, the lobes 9-19) to deeply lobed (if so, the lobes with acute apices), the sinuses extending 1/4 to 4/5 of the way to the midrib; [section Quercus; subsection Prinoideae].
............ ..8 Leaves mostly shallowly lobed at the base, the sinuses extending 1/4 to 1/2 of the way to midrib, grading into mere crenations toward the tip of the leaf, the total number of lobes/crenations usually 9-19; acorns borne on peduncles 2-10 cm long; acorn cup covering 1/3 to 1/2 of acorn, the upper scales with long-acuminate apices
............ ..8 Leaves mostly relatively deeply lobed throughout the length of the leaf, the sinuses extending 1/2 to 4/5 of the way to the midrib, the total number of lobes 3-13; acorns sessile or borne on peduncles up to 1 cm long; acorn cup covering 1/3 to 3/4 of acorn, the upper scales with acute, long-acuminate, to long-awned apices.
............ ....9 Upper scales of the acorn cups thin and acute; acorn cup covering ½ to 3/4 of the acorn; [swamps in the Coastal Plain and lower Piedmont of GA, NC, SC, and VA]
............ ....9 Upper scales of the acorn cups long-attenuate into nearly terete awns; acorn cup covering 1/3 to 1/2 of the acorn; [Mountains of VA]
............ 7 Lower surfaces of mature leaves gray, green, pale green, or yellowish, glabrescent or densely pubescent, the hairs few-branched and erect; leaves mostly relatively deeply and obtusely lobed, rarely shallowly lobed (if so, the lobes 3-7), the sinuses extending 1/2 to 4/5 of the way to the midrib, the total number of lobes 3-7; acorns sessile or nearly so.
............ ......10 Leaf lobes with acute apices; acorn cup covering 2/3 to 3/4 of acorn; [section Quercus; subsection Prinoideae]
............ ......10 Leaf lobes with obtuse to rounded apices; acorn cup covering 1/3 to 1/2 of acorn; [section Quercus; subsection Stellatae].
............ ........11 Woody twigs of the season glabrous or with scattered, deciduous 2-forked hairs; petioles of mature leaves 3-10 (-15) mm long; leaf blades (2.5-) 4-8 (-13.5) cm long, irregularly and often rather shallowly 3-5 (-7) lobed, the overall form of the leaf only rarely cruciform; largest lateral lobes usually at the midpoint of the blade (or even below it), the lobes usually not sublobed, tapering from base to tip; [xeric sandy sites in the Coastal Plain from se. VA southwards to c. peninsular and westwards to c. OK and c. TX]
............ ........11 Woody twigs of the season densely and persistently stellate-pubescent, especially toward the tip of the twig; petioles of mature leaves 15-20 mm long (Q. stellata) or 3-10 (-15) mm long (Q. boyntonii and Q. similis); leaf blades (5-) 7.5-15 (-20) cm long, usually 5-lobed, the overall form of the leaf typically cruciform (Q. stellata) or not (Q. boyntonii and Q. similis); largest lateral lobes of the leaves usually above the midpoint of the blade, these lobes either often sublobed or squarish in shape, usually wider near their tips than at their bases (Q. stellata) or not sublobed, tapering from base to tip (Q. boyntonii and Q. similis); [collectively widespread in our area].
............ ..........12 Leaves usually cruciform, the largest lateral lobes often sublobed or squarish in shape, usually wider near their tips than at their bases, and borne at right angles to the midrib; upper leaf blade surface glabrous; [usually of dry to dry-mesic upland situations, widespread in our area]
............ ..........12 Leaves not cruciform, the largest lateral lobes usually not sublobed, the lobes tapering from base to tip, and borne at ascending angles relative to the midrib; upper leaf blade surface at least sparsely stellate-puberulent (even late into the season); [of temporarily flooded calcareous swamps of the Coastal Plain, from SC (NC?) southward and westward (Q. similis) or localized on sandstone in nc. AL (Q. boyntonii)].
............ ............ 13 Rhizomatous shrubs to small trees, generally < 2 m tall; [sandstone outcrops in nc. AL]
............ ............ 13 Single-trunked large trees; [usually of temporarily flooded calcareous swamps of the Coastal Plain, from SC (NC?) southward and westward]