Australia: The Land Where Time Began

A biography of the Australian continent 

These are microscopic particles, usually of silica, but in cacti can be be calcium oxalate, that are found on the leaves and stems of many plants. The silica variety are believed to function as a support, as with the spicules of a sponge, in some species, while in others, such as grasses, they are more likely to make them less palatable to herbivores, the silica making the texture gritty. It was in response to these silica phytoliths on the grass of the plains that grazing animals such as horses evolved the high crowned teeth they have because of the abrasive nature of the of silica phytoliths.

The calcium oxalate phytoliths of cacti act as a store of carbon dioxide. During daylight hours the plant conserves water by closing its stomata. It can carry on photosynthesis with closed stomata because it stores carbon dioxide during the night when it opens its stomata, as less water is lost through the open stomata because the cooler night air results in lower evaporation rates.

Being minerals, silica or calcium oxalate, the phytoliths are not destroyed when the plant decays or is burnt. This feature, together with the great variety of shapes they come in on various plant groups, makes them good indicators of the vegetation in the area around a site. Vegetation changes can be followed by studying the changing composition of forms in sediment cores. They have been found as far back as the Devonian. Recent discovery of phytoliths from grass has been found in dinosaur dung, indicates that grass probably evolved earlier than previously thought.

Links

• Phytolith Research Institute (PRI)

• Society for Phytolith Research

Sources & Further reading