If yesterday’s Arnold Arboretum walk with Ajay Sequeira wasn’t enough for you, join Kyle Port, Manager of Plant Records at the Arnold Arboretum, on Sunday, October 2, from 9 – 1 (meet at the Hunnewell Building), and in just a few hours you can learn to identify 90 percent of the trees growing in Boston, both native and nonnative. Beginning in the classroom, 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. Register on line at www.arboretum.harvard.edu. Fee $45 member, $60 nonmember.