Inflorescence: Staminate flowers in catkins, carpellate flowers in few-flowered clusters enclosed by an involucre

Fruits: Nuts, 1-seeded, subtended or surrounded by the involucre (cupule)

Habit: Trees or sometimes shrubs, deciduous or evergreen (farther south)

Leaves: Alternate, simple, toothed or entire, with stipules

Examples:

• Castanea dentata (chestnut) [Cryphonectria parasitica, chestnut blight)
  
• Castanea mollissima (Chinese chestnut)

• Fagus grandifolia (American beech)
  
• F. sylvatica (European beech)
  
• F. sylvatica 'Atropunicea' (purple beech)
  
• F. sylvatica 'Roseo-marginata' (tricolor beech)
  
• F. sylvatica 'Pendula'

Quercus (oaks), 2 subgenera in Illinois:

Subg. Erythrobalanus (black/red oaks, acorns take 2 years to mature, leaves with bristle-tipped veins)

• Q. palustris (pin oak)
  
• Q. rubra (red oak)
  
• Q. velutina (black oak)
  

Subg. Leucobalanus) (white oaks, acorns mature in one year, leaves without bristle-tipped veins)

• Q. alba (white oak) State tree of Illinois
  
• Q. macrocarpa (burr oak)

Other oaks:

• Q. robur (cork)
  
• Q. virginiana (live oak), Think of "Gone with the Wind" and Ann Rice's "Interview with the Vampire"