Phytoliths, in essence, are plant skeletons.  The word phytolith literally means plant stone (Trussel 1999).  The phytolith itself is a tiny microscopic particle.  Its size is five nanometers or less.  The actual identification requires a compound microscope.  A phytolith is formed inside of a plant cell and most of the phytoliths found are primarily grasses (Rosen 1999).  Phytoliths are formed from opaline silica.  Silica is located in all groundwater.  While the plant is still alive, it absorbs the water with the silica.  As the water travels through the plant, the silica is deposited.  These deposits are found in the plants' leaves, cell structures, and circulatory system (Piperno 1998).  This forms the phytoliths into specific shapes for each plant species.  The opaline silica later is deposited in the soil when the plant dies.

Thomas Jefferson, besides being the third President of the United States, was an avid gardener in the early eighteen hundreds.  One of his gardening projects was at Poplar Forest, his summer home in Bedford County, Virginia (Appendix A, Figure A-1).  This home was started in 1809 and included 4,812 acres.  Today, the South lawn of the grounds of the estate holds a specific interest for studies in archeobotany.  Jefferson was known to have many ornamental plants sowed on his lawn to form an extravagant garden (Trussel 1999).  In this study, phytolith analysis was used to determine the plant life that was grown in this area during Jefferson’s time.  Soil samples from a planting hole, a French drain, and two soil layers were analyzed for phytoliths.  The layers were from sites 1812 R/3 and 1816 R/2.  The French drain sample was from site 1817 F/4, and the planting hole sample was from site 1819 F/4 (Appendix A, Figure A-2).  These samples provide an insight into how Jefferson’s garden would have appeared.

It is possible to extract the phytoliths from the soil to be identified by the archeobotanist.  Size alone cannot be used to identify a particular phytolith because certain soil conditions can distort the size of a phytolith (Rovner 1999).  This means that both structural makeup and surface features are also used to identify a phytolith.  The phytolith then is put into a general category.  Because many phytoliths have similar structures, it is then difficult to identify a phytolith at the species level.  If the phytolith can not be identified to the genus and species it is then put into one of the general phytolith categories: epidermis (puzzle pieces), hair base (sun like), nonsegmented (long with no breaks) and segmented hairs (long with breaks), scelerid (long with a forked tail), tracheid (very segmented rectangle), cystolith (looks like popcorn), spherical, or conical (hat-like). It is then further categorized into one of the three types of surface features: smooth, rugulose (rough), spinulose (spines) (Piperno 1998). The ultimate goal of the scientist is to be able to identify the plants by both genus and species (Kealhofer and Piperno 1994).