Phytoliths are microscopic plant remains that can be recovered from archaeological contexts or lake cores to reconstruct past environments and the diets of ancient peoples. In archaeology, samples can be taken from ancient tools or soils from archaeological contexts. Soil samples recovered from stratigraphy excavated during the Izapa Household Archaeology Project were processed to see how plant use and ambient vegetation at Izapa changed through time. I used the specialized facilities at Smithsonian Tropical Research Institute (STRI) to process them during my 2017-2018 postdoctoral fellowship. I am grateful for the guidance of Irene Holst and Dolores Piperno throughout the process.

Processing phytolith samples involves several steps before they can be analyzed. This includes removing clay from the samples, using mesh screens of different sizes to separate different “fractions” of material (fine, medium, coarse), cooking the samples in Hydrochloric acid to eliminate organic materials, and isolating the phytoliths through flotation. Depending on the samples, it can take several weeks to complete this process. Once they are processed, sample slides are analyzed under the microscope, where the size, shape, and other identifying features are used to identify remains of plants at the family, and sometimes even species, level.

IHAP samples during clay removal

Organic materials are removed by cooking samples in Hydrochloric acid

Different “fractions” were divided in mesh screens and placed into sample vials

Starch grains are microscopic plant remains that can be recovered from archaeological contexts to understand which plant foods ancient peoples were eating and how they were processed. From 2017-2018 I analyzed samples recovered during the Izapa Household Archaeology Project at the Smithsonian Tropical Research Institute (STRI) in Panama, where specialized facilities exist to extract and identify starch grains. In the field, residues were recovered from domestic artifacts like ceramic vessels and grinding stones. At STRI the samples were then processed in the lab with a heavy liquid (in this case, Cesium chloride) to cause these microscopic particles to float. After a series of runs through the centrifuge, a pipette is used to collect any starch grains present in the sample and place them on a slide. The slide is analyzed under a polarizing microscope, where features such as size and shape are used to identify the family or even species of plant present on the tool.

Sample tubes during processing

Yam starch grain (Dioscorea spp.) recovered from an IHAP grinding stone