People and Plants

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Paleoethnobotany

Paleoethnobotany is the study of ancient humans’ relationship with plants. It can be done at a macroscopic scale, where plants can be identified by fragments (seeds, shells, etc.) observable by the naked eye or at the microscopic scale, where microscopes are required to observe and identify plant remains. Paleoethnobotany is used to help archaeologists reconstruct ancient environments, determine what ancient peoples were eating and how they processed their food, understand when certain plants they domesticated, and identify how human relationships with their environment may have changed through time. I have worked with three different paleoethnobotanical techniques: macrobotanical analysis, starch grain analysis, and phytolith analysis. See below and check out the notes from the lab to learn more about this work.

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Me floating soils for macrobotanical remains at the New World Archaeological Foundation, summer 2013

Macrobotanical Analysis

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Close-up of a carbonized maize cob fragment

Macrobotanical analysis is used to identify carbonized plant remains from archaeological contexts. The presence of these remains can be observed with the naked eye, but microscopes are often necessary for the identification of the plant. Archaeologists take soil samples as they excavate and use a process called “flotation” to recover macrobotanical remains. Carbonized (burned) plant remains will float to the surface when immersed in water, where they can be scooped up, dried out, and analyzed by specialists. The study of macrobotanical remains can be used to reconstruct ancient diets. In cases of excellent preservation, it can even be used to identify the contents of individual pots. Because these materials are carbonized, they can also be used to date deposits using C14 (Carbon 14) dating.

 

Starch Grain Analysis

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Taking starch grain samples from ground stone pieces at the New World Archaeological Foundation, Summer 2013

Starch grain analysis is a microscopic technique that allows archaeologists to identify plant foods in the archaeological record. Starch grains are associated with carbohydrate storage in plants and can be used to identify the family or species of plants remains present in the archaeological record. Because of their high water content, it is the only way to identify many root crops (e.g. potato, yam, manioc, arrowroot) after they have disintegrated. Chemicals are used to extract starch grains from archaeological contexts, so specialized lab facilities are needed. When viewed under a microscope, individual starch grains can then be identified by characteristic features such as their size and shape. Archaeologists can look for starch grains on artifacts, like grinding stones or ceramic vessels, to understand how these tools were used. Starch grains can also be recovered directly from deposits on human teeth. Because the properties of starch grains change when they are processed, they can also provide information on food processing techniques, like cooking, heavy grinding, and fermentation. Starch grains tend to preserve well even in wet conditions and can often be recovered from sites where other plant remains disintegrate.

Maize starch grain recovered from a ground stone fragment at Izapa. Four different light settings illustrate different features that help with identification.

Phytolith Analysis

Phytoliths are microscopic particles of silica that remain in the archaeological record long after the plant has disintegrated. They are skeletons of former plant cells that can be identified by their shape and size. Because they are essentially made of glass, phytoliths preserve very well in archaeological contexts, even where other plant remains do not. Whereas starch grain analysis focuses on the “starchy” portions of the plants that people eat, phytoliths tend to be produced in the “green” parts of the plant, such as leaves, stems, and stalks. In fact, different parts of the same plant will sometimes produce different phytoliths. Unlike pollen, phytoliths generally do not travel great distances and are deposited close to where they are created. This makes them helpful tools for identifying past agricultural patterns and other localized activities. Phytolith analysis can be used to reconstruct ancient environments and to identify what plant foods people were eating based on the residues from the tools used to process and serve them. Processing samples for phytoliths involves treatment with harsh chemicals, so specialized facilities are needed.

Phytoliths recovered from IHAP samples: Left: Burned grass phytoliths, Center: palm phytolith, Right: Asteraceae (daisy family) platelet.

Postdoctoral Research at the Smithsonian Tropical Research Institute

Maize, or corn, is often considered the lifeblood of Mesoamerican peoples. But maize was just one part of a broad spectrum of plant foods that comprised the Mesoamerican diet. Ancient Mexican peoples also relied on other foods, like chili, cacao (chocolate), sweet potato, manioc, and tropical fruits to supplement their diet. While maize agriculture has often been cited as an important cultural trait that serves to unify Mesoamerican cultures, a restricted emphasis on this one food source masks the impressive regional variability in human-environmental relationships across the many environmental zones encompassed within Mesoamerica, including highlands, tropical forest, coast, and desert.

My postdoctoral project (2017-2018) applied starch grain and phytolith analysis to define which other plant foods played important roles in the diets of coastal peoples for a continuously occupied region in Mesoamerican prehistory: the southern Pacific coast of Mexico. I investigated plant remains from the site of Izapa, a settlement that was occupied for nearly 3,000 years (1900 B.C.-A.D. 1000), through droughts, volcanic eruptions, and the collapse of several prominent Mesoamerican civilizations, including the Olmec and the Maya. Ongoing documentation of the diversity of plant foods used by Izapa’s population is intended to better understand the resilience of this coastal population, especially for periods of drought and volcanic activity, when maize agriculture may have been a less reliable source of food.

The samples I analyzed were recovered from artifacts recovered during my Izapa Household Archaeology Project excavations in 2014.  These included ceramic vessels and grinding stones recovered from domestic deposits and column samples of site stratigraphy to document change through time. I undertook this research as a postdoctoral fellow at the Smithsonian Tropical Research Institute’s (STRI) Center for Tropical Paleoecology and Archaeology in Panama. Pilot studies were conducted in at the Instituto de Investigaciones Antropológicas at the Universidad Nacional Autónoma de México (UNAM).

 

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