In all of his publications on Thai orchids, Seidenfaden referred to the seven floristic regions of Thailand by a sequence of Roman numerals. In The Seidenfaden Database of Orchids and in Flora of Thailand, the same regions are referred to as "northern", "north-eastern" etc. However, in the subsections on species occurrence in some of the Flora of Thailand instalments, the seven floristic regions are designated by Roman numerals, using a numbering system that is different from the system used by Seidenfaden. The Flora of Thailand numbering system has been adopted by a number of authors (including orchidologists such as Obchant Thaithong) who have used them in other publications. The different numbering systems are compared below:
Left, Gunnar Seidenfaden, 1974 (photo by Rigmor Mydtskov, courtesy of the Royal Danish Academy of Sciences and Letters)
The Seidenfaden Database of Orchids is an electronic register of the spirit-preserved orchid specimens and the original line drawings and colour slides of orchids that make up part of the Seidenfaden collection at the Natural History Museum, University of Copenhagen. The renowned orchidologist and former Danish ambassador to Thailand, Gunnar Seidenfaden (1908–2001) was the main responsible for changing the Thai orchid flora from one of the least known to one of the best known orchid floras in tropical Asia. In his later years, he also published important revisions of the orchid flora in former Indochina, Peninsular Malaysia/Singapore and certain parts of India.
When Seidenfaden passed away, we lost not only the world's leading authority on the orchids of the Southeast Asian mainland, but also a former high-profile diplomat and one of the last pioneering explorers of the Arctic. Several obituaries and other papers on Seidenfaden and his collections exist; Friis (2002) compiled a list of Seidenfaden's scientific publications and provided particularly comprehensive information on his career. For biographical information, visit also Wikipedia. Seidenfaden left all of his spirit samples, original illustrations and working file to what is now the Natural History Museum of Denmark – together with a generous amount of money for the reorganization and future utilization of the material. Already in 2002, The Seidenfaden Database of Orchids was designed for registration of the diverse orchid-related material, and the registration of spirit samples, colour slides and line drawings was completed during the following years. Now the database is accessible online for searching among more than 11,000 spirit samples, 3,000 original line drawings and 7,000 colour slides in the Seidenfaden collection.
The concept of The Seidenfaden Database of Orchids was developed by Henrik Æ. Pedersen, Christian Lange, Katja Anker and Ib Friis; programming and graphics were done by Christian Lange, and Henrik Æ. Pedersen wrote the explanatory texts. Data were entered by Katja Anker, Lene K. Skougaard, Linnea Fosdal, Marie E. Hessellund, Stine K. Jacobsen og Carsten S. Madsen.