| 1. | Leaves oval, not lobed. | Quercus imbricaria Shingle oak |
| 1. | Leaves variously shaped, always with distinct lobes. | [2] |
| 2. | Lobes of leaves sharp pointed, bristle-tipped; acorns maturing on 2nd year's growth, cupules with scales flattened throughout. | [3] [Red Oak Group] |
| 2. | Lobes of leaves rounded, bristle-tips lacking; acorns maturing on current year's growth, cupules with scales commonly tuberculate at base. | [7] [White Oak Group] |
| 3. | Marginal scales of acorn cup forming a loose fringe; terminal buds large [5-12 mm], sharply angular in cross-section, with dense appressed pubescence throughout; inner bark typically yellow to orangish. | [4] |
| 3. | Marginal scales of acorn cup tight; terminal buds shorter [typically < 8 mm], slightly angled to round in cross section, glabrous or with pubescence isolated to apical 1/2; inner bark typically reddish. | [5] |
| 4. | Leaf blade primarily 3-lobed, much expanded at the apex [like a duck's foot], w/≤ 10 bristles, leaf base rounded to cordate; petioles short [usually < 1cm]; recorded only from the southern-most two tiers of counties in the state. | Quercus marilandica Blackjack Oak |
| 4. | Leaf blade primarily 5 or more lobes separated by sinuses usually extending > 1/3 way to the midrib, ovate to obovate in outline, but not expanded as above, w/> 10 bristles, leaf base somewhat pointed to truncate at the petiole; petioles longer [> 2 cm]; rare to absent in the NW corner of the state, otherwise more common. | Quercus velutina Black Oak |
| 5. | Acorns 1.3 cm long or shorter, broader than long to nearly spherical; cupule saucer-shaped;
leaf blade bearing conspicuous tufts of tomentum in vein axils of lower surface, with lowest pair of lobes
commonly recurved; terminal buds glabrous or nearly so. | Quercus palustris Pin Oak |
| 5. | Acorns 1.3 cm long or longer, longer than broad; cupule various; leaf blade lacking recurved lobes, tufts of tomentum on lower surface absent or less conspicuous; terminal buds glabrous or more often bearing at least an apical tuft of pubescence. | [6] |
| 6. | Upper leaf surface dull green and lower surface often glaucous, sinuses usually extending
< 1/2 distance to midrib, distal end of lobes forming an acute angle; terminal bud usually
with at most an apical tuft of pubescence; cupule saucer-shaped to deeper, covering ≤ 1/3 of the essentially ovoid nut. | Quercus rubra Red Oak |
| 6. | Upper leaf surface shiny and lower surface not glaucous; sinuses usually extending > 1/2
distance to midrib, distal end of lobes expanded; terminal bud most often bearing
pubescence on apical 1/2; cupules deeper, covering 1/3 - 1/2 of nut, nut ellipsoid to ovoid in silhouette. | Quercus ellipsoidalis Hill's Oak |
| 7. | Leaves usually deeply lobed, sinuses primarily extending 1/3 - 1/2 distance to midrib. | [8] |
| 7. | Leaf margin sinuate to dentate, but not deeply lobed. | [11] |
| 8. | Leaf blade essentially glabrous at maturity. | [9] |
| 8. | Leaf blade pubescent at maturity. | [10] |
| 9. | Leaf base cordate; acorns usually with long [3-8 cm] slender peduncle; a native of Europe introduced in Des Moines, Johnson, Poweshiek, & Story counties [an probably others]. | Quercus robur English Oak |
| 9. | Leaf base extending along petiole, not cordate; acorns sessile or peduncles stout and < 3 cm; Iowa native absent from NW corner, rare to common elsewhere. | Quercus alba White Oak |
| 10. | Terminal leaf lobe typically expanded greatly [fan-shaped], leaf sinuses of basal 1/2 of leaf deep, those of upper half shallower to merely sinuate; acorn cupule large, with loose fringe-like bracts; nut ≥ 1.5 cm long; throughout the state. | Quercus macrocarpa Bur Oak |
| 10. | Terminal leaf lobe not fan-shaped, blade commonly cruciform; acorn cupule small, loose fringe-like bracts lacking; nut ≤ 1.5 cm long, fresh nut scar commonly salmon-colored; restricted to southern 2 tiers of counties. | Quercus stellata Post Oak |
| 11. | Acorns on peduncles 1-5 cm long, cupule sometimes with a few loose fringe-like bracts [far less prominently as with Q. macrocarpa]; lower leaf surface with appressed-stellate and erect long hairs, often velvety to the touch; leaves whitened beneath; bark of 1-2 cm diameter branches ± peeling longitudinally. | Quercus bicolor Swamp White Oak |
| 11. | Acorn on penducles ≤ 1 cm long, cupule lacking fringe; lower leaf surface with at most appressed-stellate pubescence and green in color; branch bark tight, not peeling. | [12] |
| 12. | Leaves with ≤ 9 veins per side; acorns produced on shrubby plants [height typically ≤ 12 feet]; commonly associated with sandy sterile soils; rare, recorded from 13 counties in SC & SW Iowa. | Quercus prinoides Dwarf Chinquapin Oak |
| 12. | Leaves with ≥ 10 veins per side; acorns produced on trees [height greater than above]; commonly associated with limestone; varying in abundance from rare to common in the SE 1/2 of the state. | Quercus muehlenbergii Chinquapin Oak |
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| "Think of the fierce energy concentrated in an acorn! You bury it in the ground, and it explodes into an oak! Bury a sheep, and nothing happens but decay." --- George Bernard Shaw |