Washing groundstone for pollen, starch, and phytoliths is a much more direct measure of plants that might have been processed, than collecting sediments under or next to groundstone. We have developed methods of washing groundstone to minimize recovery of post-depositional sediment, thus reducing the added background signature. If it is possible to wash groundstone or ceramic sherds or vessels to recover pollen, phytoliths, or starches that might represent plants processed, this should be done. Sediment samples can be collected as controls.
Examples of pollen recovery from groundstone include maize/corn, beeweed, Cheno-ams, mustard family, cattail, and many other plants. Washing groundstone for evidence of food processing provides evidence not only that a particular plant was processed, but that grinding was part of the processing.
To date we have examined relatively few groundstone for phytolith evidence of plant grinding. Calcium oxalate raphids produced by cattail roots also were recovered from groundstone. Other than maize/corn phytoliths and cattail raphids, no other examples of foods have been recovered yet.
Starches should be "food for bacteria and other soil micro-organisms", but as with all things in nature, it is an imperfect system. Some of the starches simply survive. Starches provide a particularly good record of grinding roots/tubers because these foods do not leave seeds or pollen. When roots/tubers are collected when the plants are in flower, the flowers transport pollen to the processing area, which allows portions of the pollen record to represent collection and processing roots/tubers. However, when roots/tubers are not collected when the plants are in flower, there is no transport mechanism. Many starches survive our pollen extraction process, meaning that we can identify them when we see them in pollen samples. As a general rule, starches from roots/tubers have eccentric hila (that means their hilum, which often appears as a dark spot under the microscope) is off-center. Seeds, on the other hand, usually produce starches with centric hila. We have not observed Cheno-am starch in the record, although we have seen many maize/corn-type starches in groundstone wash samples. A cross-polar illuminator (or crossed nichols) are necessary to examine starches well enough to identify them. Some starches have a rather generic form, while others are specific to either genus or species. Many plants produce several different types of starches in a single organ, meaning that one must learn to identify populations of starches, rather than relying on single starches. We have noted starches in human tooth calculus, groundstone washes, ceramic washes, washes of Poverty Point Objects, floor samples, other sediment samples, and in nearly every type of provenience that we have examined for evidence of food processing.