Participants in the USA National Phenology Network’s (USA-NPN) Nature’s Notebook (NN) program select and observe species from a large list of plant and animal species. This national effort to collect standardized ground observations of the phenological phases—or observable life cycle stages—of species by researchers, natural resources managers, students and volunteers, supports a wide range of scientific applications and management decisions routinely made by citizens and professionals. High quality data is vital to this effort and this guide is meant to acclimate participants to information referenced within the Nature’s Notebook program. The botanical information covered in this document will help observers make reliable plant observations.