Key to the Oaks of Iowa

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

Chinquapin Oak

Plants of Iowa Homepage

Recommended Plant Image Websites

Return to the Previous Page

"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

Valid XHTML 1.0 Strict