He made several collecting trips to
Italy,
Crete,
Greece,
Egypt and
Palestine followed by a two-year-long expedition to Australia,
Mauritius and
South Africa, collecting not only plants, but also animals, art and
ethnographic objects. He spent seven months in
Sydney (then more usually called
Port Jackson) from 1 June 1823 until December 1823 where he collected 645 local plant specimens. He never reached the Western hemisphere (in contradistinction to Friedrich Wilhelm Sieber, an employee of
Johann Centurius Hoffmannsegg), but sent several people to make collections for him, notably
Franz Kohaut in the
Antilles and
Wenceslas Bojer,
Carl Hilsenberg on Mauritius and
Karl Ludwig Philipp Zeyher in South Africa. Sieber distributed many
herbarium specimens in more than 25 specimens series which resemble
exsiccatae. The two largest by number are entitled
Herbarium florae Austriacae and
Herbarium florae Novae Hollandiae. ==Later life and death==