Franz Thonner
![Vienna 1910 (photograph by [[Ludwig Grillich](https://upload.wikimedia.org/wikipedia/commons/c/c6/Franz_Thonner01.jpg)
He was a scientist of independent means who explored Europe and North Africa and in 1891, at age 28, privately published a key to the families of flowering plants of the world. Despite the work's having been translated into English in 1895, it was largely ignored in that country. A second edition of his key appeared in 1917 and was based on Engler & Prantl's ''Die Natürlichen Pflanzenfamilien'' and ''Das Pflanzenreich''.
Thonner's German plant key of 1891 was translated into English for the second time in 1981, and became more accessible to English-speaking botanists, rivalling that of John Hutchinson and ''Families of Angiosperms'' by Bertel Hansen & Knud Rahn (1969). The key covers gymnosperms and angiosperms and was designed for field use. Thonner also used back-up features ensuring correct choice of the family even when there is uncertainty about classifying botanical structures. Geographical distribution is used to assist in identification.
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