| A. | Pith of twigs chambered, interrupted by crosswalls; nut with a distinctly furrowed shell, husk not splitting into sections, husk rotting away from nut with age after fruit-fall. | Juglans Butternut & Walnut |
| A. | Pith of twigs solid, crosswalls lacking; shell of nut with a ± smooth surface, husk splitting into four sections at maturity. | Carya Hickory |
| Carya: Hickories | ||
| 1. | Terminal bud scales valvate, not over-lapping [2 scales visible, meeting at edges & essentially not overlapping]. | [2] |
| 1. | Terminal bud scales imbricate [> 2 scales visible & overlapping]. | [3] |
| 2. | Mature leaves commonly with ≤ 9 leaflets; buds yellow; nut essentially spherical, husk splitting to approximately the middle of the nut. | C. cordiformis Bitternut Hickory |
| 2. | Mature leaves commonly with ≥ 11 leaflets; buds brownish; nut cylindrical, husk splitting to the base of the nut. | C. illinoinensis Pecan |
| 3. | Leaves primarily with 5 [or fewer] leaftlets. | [4] |
| 3. | Leaves primarily with 7 [or more] leaftlets. | [5] |
| 4. | Teeth of leaflets bearing tuft of pubscence just beneath tooth apex; nut usually > 3.5 cm; husk of fruit thick [typically ≥ 0.5 cm], splitting to base of fruit at maturity; mature bark shaggy, splitting vertically into long loose plates; widespread in the state. | Carya ovata Shagbark Hickory |
| 4. | Teeth of leaftlets lacking tuft of pubescence; nut usually < 3.5 cm; husk of fruit thin [typically ≤ 0.5 cm], splitting to approximately the middle of the fruit; mature bark tight, becoming deeply furrowed with age, not shaggy; reported from SE Iowa [Van Buren county]. | Carya glabra Pignut Hickory |
| 5. | Mature bark shaggy, splitting vertically into long loose plates; leaves ≥ 60 cm long; fruits typically ≥ 5 cm long; twigs stout. | Carya laciniosa Shellbark Hickory |
| 5. | Bark ridged to deeply furrowed, not shaggy; leaves ≤ 60 cm long; fruits typically ≤ 5 cm long; twigs stout or slender. | [6] |
| 6. | Leaves typically bearing ≥ 7 leaflets; lower leaf surface, petiole, and leaf rachis ± densely pubescent; husk of nut splitting to base of fruit; twigs stout; reported from SE & SW corners of Iowa. | Carya tomentosa Mockernut Hickory |
| 6. | Leaves typically bearing ≤ 7 leaflets; lower leaf surface, petiole, and leaf rachis essentially glabrous; husk of nut splitting to middle of fruit; twigs slender; reported from SE Iowa [Van Buren county]. | Carya glabra Pignut Hickory |
| Juglans: Butternut & Walnut | ||
| 7. | Pith of twigs chocolate brown; nut elliptical, surface sticky-hairy; leaf scar with linear moustache-like upper edge. | Juglans cinerea Butternut |
| 7. | Pith of twigs tan; nut spherical, the surface smooth; leaf scar lacking linear moustache-like upper edge. | Juglans nigra Black Walnut |
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