Populus

Species of Populus display leaf blade heterophylly along the branchlet over the growing season. Those leaves that overwinter in the winter in bud and expand in the spring are called first leaves (or preformed) vs. those leaves that are produced later in the season as the growing shoot continues to expand, which are called new leaves (or neoformed). As these leaves can vary in size, shape, and number of marginal teeth, it is important to collect both types when possible. Greatly enlarged leaves produced on vigorous shoots are not accounted for in the identification key. Reference: Eckenwalder (2010).