World Checklist of Selected Plant Families: http://apps.kew.org/wcsp/
Plants of the World On-line database http://plantsoftheworldonline.org/.
Royal Horticultural Society (RHS). http://apps.rhs.org.uk/horticulturaldatabase/orchidregister/orchidregister.asp.
RHS list of names of genera and nothogenera https://www.rhs.org.uk/plants/pdfs/plant-registration-forms/list-of-orchid-genera-with-components.pdf
RHS. index to abbreviations of genera and nothogenera https://www.rhs.org.uk/plants/pdfs/plant-registration-forms/orchid-name-abbreviations-list.pdf
International Register and Checklist of Orchid Hybrids. https://www.rhs.org.uk/about-the-rhs/pdfs/publications/orchid-hybrid-lists/orchid-reg-nhl-1319-apr-jun-2017.pdf.
Robertson Orchid Nursery – Queensland Australia
Orchid Species Plus Species Orchid specialist
Global Orchid info. great site, photos & info on species & hybrids you can submit your own photos etc.
Orchidaceous Books – Suppliers New & used Books – CD ROMs – Orchid supplies
Orchid Species Photographs by Eric Hunt