Occurrence of Characeae in Switzerland over the last two centuries (1800-2000)

Some 3100 specimens of Characeae from herbarium collections and recent sampling programmes in Switzerland were redetermined and their provenance analysed, in order to investigate historical changes in frequency, distribution and current status of the species. Altitudinal and geographic distribution patterns of 27 taxa are described in 125 km(2) grid squares covering Switzerland, and an analysis was made of species richness of Characeae in different grid squares. Data were available for approximately half (117 out of 262) of the grid squares covering Switzerland, showing that the recording effort had not been uniform. The lowland was better investigated than either the hills or the mountains. And 17 taxa were categorised as rare, on the basis that they were each known from <100 records. Ten taxa were classified as not uncommon, among which Chara vulgaris and C. globularis are the most frequent and widespread species. The distribution of some species shows a significant relationship with altitude, but analysis of the species distributions shows only a weak relationship with altitude of the grid square and biogeographical region, revealing that these two variables are not the main factors explaining the distribution of the species. Over the last 200 years, regression has occurred in the species that were formerly the rarest and expansion has occurred in a few species that were previously the most common, Further investigations are needed to precise the distribution of the declining species, particularly in the under-prospected parts of the country and in poorly known habitats. (C) 2002 Elsevier Science B.V. All rights reserved.