X-ray microanalysis was employed to screen biogenic plant silica extracted from the aboveground tissues of 20 species (Grammeae Cyperaceae. Ericaceae, and Coniferae) occurring in subalpine and alpine grasslands, heaths, and woodlands on siliceous bedrock in Valaisan Swiss Alps. Among the taxa Investigated. only woody species produced a high proportion of phytoliths containing aluminum in the form of aluminosilicates This difference between the chemical composition of wood and that of herbaceous phytoliths has important implications for the sourcing, of phytoliths As applications for palaeoenvironmental Studies can be expected to he far-reaching, the potential of this microanalytical technique is discussed.