In just a few hours on Saturday, June 1, you can learn to identify 90 percent of the trees growing in Boston, both native and nonnative. Beginning at 9 am in the classroom in the Hunnewell Building of the Arnold Arboretum, you will briefly review the characteristics of the 25 most common trees and learn the botanical terminology necessary to describe them. You will then walk the grounds of the Arboretum to look at mature specimens of these trees. The class will be given by Kyle Port, Manager of Plant Records at the Arnold Arboretum. Fee $45 Arboretum member, $60 nonmember. Register on line at www.my.arboretum.harvard.edu.