I found these online sources useful for both Around the World in 80 Trees and Around the World in 80 Plants.
There is a separate page with a General Bibliography, and a list of Individual Species Pages for each species featured in Around the World in 80 Plants.
Particularly important resources are highlighted with bold text and an asterisk *.
- Australian Native Plants Society
- Bean’s Trees and Shrubs
- Botanic Gardens Conservation International (BGCI) *
- Botanist in the Kitchen
- Botany One
- BRIT, Native American Ethnobotany Database
- CABI Invasive Species Compendium *
- Cambridge University Botanic Garden
- Champion Trees Worldwide
- Early English Books Online *
- Encyclopedia of Life (EOL) *
- Endemic Species of the World (‘Living National Treasures’)
- Finland Botany Portal (‘NatureGate’)
- Forests and Climate Change (FAO)
- Gymnosperm Database
- In Defense of Plants
- International Plant Name Index *
- Maori Plant Use database
- Missouri Botanical Garden
- Native Tree Society (North America)
- New Zealand National Library
- PalDat, Palynological Database
- Plant Image Search – Arnold Arboretum
- Plants of the World Online from the Royal Botanic Gardens, UK *
- Royal Botanic Gardens, Kew
- Plants for a Future
- Russia Agro-Atlas
- Science.Gov, USA
- Science Daily *
- Society for Economic Botany *
- USDA Plants database
- Wellcome Library
- Wood database
- World Checklist of Selected Plant Families (WCSP, from Kew Science)