The simple leaves are finely toothed. The fruit is a small samara. Birch differs from alder (Alnus) with a female catkin is not woody and will not fall apart.
Birch twig
Steve Nix
Birch (Betula Spp.) - Alternate Ranked
Often confused with beech, hophornbeam, alder and ironwood.
Has short, scaled buds (vs.# long, scaled buds on beech).
Male and female parts on same tree (male long catkins, female short cones).
Has no catkins.
Yellow birch has wintergreen tasting twig.
River birch has salmon colored exfoliating bark.
Paper (canoe) birch has creamy white thin bark separating into papery strips.