Solfataras, Fumaroles.—Whereas the halophytic vegetation of deserts and steppes consists chiefly of xerophytes, the plant communities of solfataras and fumaroles show a mesophytic character throughout. The vegetation of the sulphur springs of Java has been given much attention, even to the structure of tissues. There the soil surface is covered with a yellow and whitish coating of sulphur and sulphur compounds. The steaming springs are rich in alum. The beautiful fern, Pteris incisa, nowhere thrives better than upon these soft sulphurous soils; Polypodium vulcanicum even ventures upon rocks which are occasionally flooded by water reaching a temperature of 75ºC. According to Holtermann (1907, p. 78), the dominant shrubs, Agapetes vulgaris and Rhododendron retusum, are completely covered with a yellowish precipitate from the sulphurous fumes. In spite of it, however, the leaves retain a rich green color, and even in the warm mud, surrounded with boiling solfataras, the shrubs bloom and bear fruit. The leaf anatomy of all the species examined is remarkable for the absence of xerophytic structures. (Braun-Blanquet 1932:203)
In the spring purple bacteria form communities upon the mud bottom of the lagoons near Montpellier. When the inch-thick algal mat of species of Ulva and Enteromorpha is removed, large areas of the moist soil appear covered with an intensely wine-red, ill-smelling carpet of bacteria. A survey of the sulphur bacteria, with extensive references, is given by Düggeli (1919). (Braun-Blanquet 1932:203)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.