Director Rupert Toovey spotted Blüten und Insekten Nr. 3 among a stack of dusty pictures on the floor on a routine visit to a house near Petworth. Most of the items were described as "traditional English country house taste".
The 19 x 15in (49 x 38cm) oil on wood panel was understood to have been in the family for several generations and the vendor was unaware that it might be valuable. The condition was good, apart from some minor cracking and dirt on the surface.
Signed with initials and dated 1935, it was accompanied by a label on the verso indicating that it was shown at the Vienna Secession's autumn exhibition of the same year.
It was one of a series of works in which Sedlacek explored the theme of fantastical flowers and insects - the title translates asTrumpet Blooms and Insects.
Estimated at £50,000-80,000 for the auction on June 17, the contest was taken up by three phone bidders. It eventually came down to a competition between a leading Viennese gallery and a private German collector, selling to the latter at £85,000.