The United States Botanic Garden is hosting a holiday exhibit titled “Season’s Greenings: National Parks and Historic Places,” celebrating the 100th anniversary of the National Park Service and the 50th anniversary of the National Historic Preservation Act. In their model train show, the trains chug around, below, through and above recreations of iconic national parks and sites in the National Register of Historic Places, all made from plants and other natural materials. The West Gallery houses a large indoor tree decorated with national park ornaments as well as a model of the Old Faithful Inn and geyser. In the Garden Court are model landmarks from the nation’s capital, again all made from natural materials, along with more than 30 varieties of poinsettias featuring old and new forms and colors.