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Phytolith ("Plant stone") is a rigid microscopic body that occurs in many
plants. The most common type of phytolith is the
silicon phytolith, also called
opal phytolith. Silicon phytoliths vary in size and shape depending on the plant taxon and plant part (
stem,
leaf,
root) in which they (naturally) occur.
Grasses, including
rice,
wild rice,
maize, wheat, and other various grains); crop plants such as beans, squashes, gourds, manioc, canna, and arrowroot; palms; as well as numerous tree species are just some of the plants which contain phytoliths.
Calcium oxalate phytoliths are another common type, occurring in the stems of
cacti and
baobabs. Phytoliths are mentioned in the writings of
Charles Darwin.
These objects serve a variety of purposes. In many cases, they appear to lend the plant structure and support, much like the spicules in sponges and leather corals. Others serve to make plants distasteful, lending the plant's tissues a grainy or prickly texture. Finally, calcium oxalate phytoliths serve as a reserve of carbon dioxide. Cacti use these as a reserve for photosynthesis during the day when they close their pores to avoid water loss, while baobabs use this property to make their trunks more flame-resistant.
Phytoliths are very robust in nature, and are useful in archaeology, since they can be used to reconstruct the plants present at a site or an area within a site even though the rest of the plant parts have been burned up or dissolved. Because they are made of the inorganic substances silica or calcium oxalate, phytoliths don't decay when the rest of the plant decays over time and can survive in conditions that would destroy organic residues. Phytoliths can provide evidence of both economically important plants and those that are indicative of the environment at a particular time period.
Phytoliths may be extracted from residue on many sources dental calculus (buildup on teeth); food preparation tools like rocks, grinders, and scrapers; cooking or storage containers; ritual offerings; and garden areas.
