The reason given was that many of the specimens have become quite rare and the aim is to multiply as many species as possible in sufficient scale so that young plants can be returned to their country of origin.

The first trip of the Three-year Expedition sailed with the Royal Greenland Trading Department vessels Gustav Holm, named after the homonymous officer and explorer, and the Godthaab, a 287 tons displacement ship, built after a plan designed by Fridtjof Nansen, and including seaplanes borrowed from the Danish Navy.

During the expedition, Eigil Nielsen, a vertebrate palaeontologist, studying the Upper Permian beds of Cape Stosch, in the fjord of Godthab Gulf in King Christian X Land, stumbled upon the first fossils of specimens of the taxon Fadenia, which he named after Seidenfaden.

Some 184 issues of the newsletter were produced in all until the end of the war, and one copy made its way to Stockholm every day on the daily German courier plane from Copenhagen, picked by insiders at Stockholm's Bromma airport and delivered to Dansk Presse Tjeneste, the illegal news bureau in which Gunnar's brother Erik Seidenfaden worked.

After returning to Copenhagen for five years, he was stationed in Bangkok, Thailand, from where he acted as ambassador to Manila (Philippines) from 1955, Rangoon (Burma) and Phnom Penh (Cambodia) in 1956 as well as to Vientiane (Laos) in 1957.

[2] During his time in Thailand, he initiated a long-standing cooperation with the Royal Thai Forest Department, with which he arranged a number of collecting expeditions until the mid-1980s.

He was the son of district attorney and Copenhagen's chief constable Aage Valdemar Seidenfaden (1877–1966) and Anna Elise Reenberg Teilman Harck (1887–1928).

The Royal Danish Navy operates the 1.660 tons environmental vessel A561 Gunnar Seidenfaden, the second of the two such ships, which was named after him as a botanist.

The vessel, which is painted in orange-red and cream colors to indicate their civilian purpose, has been on many occasions been deployed to fight oil pollution in Danish waters and also abroad, such as in 2002, when it participated in the clean-up after the sinking of the tanker Prestige off the northwest coast of Spain.