GROUP I: Leaves simple, alternate, deciduous, 2-ranked, with one main vein.
KEY TO GENERA
1. Leaf blade margin entire, rarely coarsely lobed or wavy toothed ....................................................... 2
2. Lateral twig base obviously nearly surrounded by leaf scar, stem appearing jointed. Lateral buds hidden by petiole base ............................. Dirca
2. Lateral twig base not appearing jointed. Lateral buds evident between twig and petiole or above leaf scar .....................3
3. Pith diaphragmed, chambered, or space empty .......................................................... Asimina
3. Pith continuous and lacking diaphragms .............................................................................. 4
4. Bud scales silky-hairy on back, uncommonly partly so on outer two scales ......................................... Stewartia
4. Bud scales glabrous or hairs other than silky (See GROUP J) ................................. Gaylussacia
1. Leaf blade margin crenate or serrate to dentate or undulate .............................................................. 5
5. Lateral buds superposed at some or all nodes ..................................................................... Stewartia
5. Lateral buds solitary and/or rarely collateral, not superposed ............................................................. 6
6. Some lateral buds stalked ............................................................................................ Fothergilla
6. All lateral buds sessile .............................................................................................................. 7
7. End bud on most twigs a terminal one ................................................................................ 8
7. End bud an axillary one ................................................................................................. Corylus
8. Bud scales silky-hairy, bundle scar 1 in leaf scars ..................................................................... Stewartia
8. Bud scales not silky-hairy, bundle scars 3 in leaf scars .................................................. 9
9. Buds mostly slightly curved laterally; flowers and fruits in racemes ...................................... Amelanchier
9. Buds mostly straight; flowers and fruits in cymes (See GROUP K) .................................... Aronia