• Woodland Trust
  Twigged - A guide to your trees through the seasons

• University of Florida
  680 fact sheets

• Barlett Tree Experts
  Tree species

• Forestry and Land Scotland
  Trees

• The Conservation Volunteers
  Identifying trees

• The Wildlife Trusts
  Trees and Shrubs

• Woodlands.co.uk
  A Guide to Tree Identification

• Woodland Trust
  A-Z of British Trees

• Tree Guide
  Tree-guide.com

• The Conservation Volunteers
  Identifying trees

• Forest Research
  Tree Species Database

• Tree of Life Project
  Tree of Life Web Project

• NatureScot
  Native versus non-native woodland

• Botanic Gardens Conservation International
  Global Tree Search

• Tree Library
  TreeLib

• Forestry Images
  Image library

• SEINet Portal
  Image library

• Tree Guide UK
  Tree identification keys

• Natural History Museum
  UK Tree identification guide

• OPen Air Laboratories (OPAL), Imperial College London
  Tree Identification Guide

• Science And Plants for Schools
  A key for identifying British Trees and Shrubs

• Forest Research
  Identifying Broadleaved Trees in Winter

• Pl@ntNet
  Image identification

• Woodland Trust
  Tree ID app

• LeafSnap
  LeafSnap

• PlantSnap
  PlantSnap

• iNaturalist
  Seek

• Botanical Society of Britain and Ireland
  Introduction to Conifer ID

• Chilterns National Landscape
  Tree ID Training with John Morris

• Ecology Training UK
  How to identify common British trees

• Forest Research
  Introduction to Conifer ID

• Iowa State University
  Interactive Tree Identification Key

• Forest Commission Scotland
  Scotland's Native Woodlands Annex Annex 1 Tree and shrub species native to Scotland

• Non-native species secratariat
  Non-native ID sheets

• Non-native Species Secretariat
  ID Sheets non-native spcies

• Scottish Invasive Species Initiative (SISI)
  Invasive Plant Project
  

Taxonmy

• Tree Of Life
  Tree Of Life web project