The flora of the South Sandwich Islands, with particular reference to the influence of geothermal heating

Aim To carry out as comprehensive a survey as practicable of the flora (hig her plants, mosses, liverworts, lichens, basidiomycete fungi and diatoms) o f the isolated, volcanically active, South Sandwich Islands archipelago in the southern South Atlantic. To relate the components of this flora to (1) the influence of local geothermal heating and (2) wider regional floras. Location South Sandwich Islands, southern South Atlantic Ocean, maritime An tarctic (56-60 degrees S, 26-28 degrees W). Methods Ice-free accessible sites on all 11 of the major islands in the arc hipelago were visited by helicopter in January 1997. During each visit, vou cher specimens of each floral group were collected. The comprehensiveness o f collections obtained at each site varied with the duration of each visit (a function of tight logistic constraints) and extent of site, Visit durati on varied from 1 to 9 h at most sites, with longer periods spent on Belling shausen Island (2 days) and Leskov Island (1 day). Candlemas Island was exa mined in greater detail over a 4-week period in February 1997. At all sites , particular attention was given to areas influenced by geothermal heating. Results Data obtained in 1997 are combined with updated records from the on ly previous survey (in 1964) to provide a baseline description of the flora of the archipelago, which currently includes 1 phanerogam, 38 mosses, 11 l iverworts, 5 basidiomycete fungi, 41 lichenised fungi and 16 diatoms with, additionally, several taxa identified only to genus. Major elements of the moss and liverwort floras are composed of South American taxa (32% and 73%, respectively), with a further 45% of mosses having bipolar or cosmopolitan distributions. These two groups show low levels of Antarctic endemicity (1 1% and 18%, respectively). In contrast, 52% of lichens and 80% of basidiomy cete fungi are endemic to the Antarctic. A further 36% of lichens are bipol ar/cosmopolitan, with only 5% of South American origin. Main Conclusions The flora of the South Sandwich Islands is clearly derived from those of other Antarctic zones. The flora of unheated ground is close ly related to that of the maritime Antarctic, although with a very limited number of species represented. That of heated ground contains both maritime and sub-Antarctic elements, confirming the importance of geothermal heatin g for successful colonisation of the latter group. The occurrence of severa l maritime Antarctic species only on heated ground confirms the extreme sev erity of the archipelago's climate in comparison with well-studied sites mu ch further south in this biogeographical zone.