The Study of Plant Evolution

Sunrise through an oak-hickory forest canopy at Tyson Research Center, Washington University in St. Louis, Missouri. (Jonathan Myers)

The leaves of a sugar maple start to yellow as winter approaches, Tyson Research Center, Washington University in St. Louis, Missouri. (Jonathan Myers)

An ornamental cherry tree loses its leaves in the fall at the Tidal Basin, Washington, DC. (Amy Zanne)

A frost covered dandelion head spreads as winter arrives at the University of Idaho Arboretum, Moscow, Idaho. (Simon Uribe-Convers)

A birch leaf turns a bright yellow as winter approaches, Gateway Arch, St. Louis, Missouri. (Amy Zanne)

Maple leaves change colors before they fall in Rock Creek Park, Washington, DC. (Amy Zanne)

Early winter brings out the reds and oranges on sugar maple trees at the Gateway Arch, St. Louis, Missouri, USA. (Amy Zanne)

Buckeye leaves emerge in the spring after the winter frost at Forest Park, St. Louis, Missouri. (Amy Zanne)

Newly emerged tulip poplar leaves in spring after winter frost at Joyce Kilmer Memorial Forest, Robbinsville, North Carolina. (Amy Zanne)