Betula nigra catkins long, the male catkins pendulous, the female catkins erect. The fruit is unusual among birches in maturing in late spring; it is composed of numerous tiny winged seeds packed between the catkin bracts. "Betula nigra" is a tree that falls into the family of Betulaceae, which is commonly known as the Birch or Alder Family. This family comprises six genera ("Alnus, Betula, Carpinus, Corylus, Ostrya," and "Ostryopsis)" and includes alders, birches, hornbeams, and hazelnuts. Species within this family, along with "Betula nigra", are shrubs or trees that grow along stream sides or in poorly drained soils throughout the Northern
Pterocarya fraxinifolia appear in April, the male catkins thick and green, 7.5 – 12.5 cm long, the females longer with less dense flowers, bearing red styles forming fruiting catkins 30 – 50 cm long, the green, winged, nuts approximately 1.8 cm wide. The species is fast growing and grows best on flat ground or shallow slopes near river banks and in deep moist soils. The climate associated with the distribution of this tree includes mild winters and mild humid summers. It generally grows in mixed stands with other species and rarely grows in pure stands. Fossils of "Pterocarya fraxinifolia" have been described