As part of a floristic mapping, the territory of the Sihl Valley between the city of Zürich and Höhronen was mapped by the Institute for the conservation of the Canton of Zürich on an area of 249 km2. The so-called report Flora des Sihltals von der Stadt Zürich bis zum Höhronen includes 2109 species, including 611 frequent crops and ornamental plants or accidentally introduced species which grow wild at most locally and in the short term. 1498 species are, or were at least 30 years during the last 160 years in stable populations exist. Of which 177 or 13% are now extinct, and 284 have been re-introduced and introduced. In all, the flora has become more species-ric, however, 42% of the previous species have decreased and only 30% show an increasing trend.