The Science of Seeds

Joyce White, director of an archaeological project studying a UNESCO World Heritage Site in Thailand, reveals the scientific methods archaeobotanists use to unlock the secrets contained within plant remains excavated from archaeological sites.

By Joyce White

July 16, 2024

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Dr. Prachaya Srisanga from the Queen Sirikit Botanic Garden in Chiang Mai, Thailand, examines a mounted botanical specimen at the Penn Museum collected by the author more than 40 years ago from the Ban Chiang region. Dr. Srisanga is the taxonomist for the Year of Botany’s ethnobotanical study; photo by Kellie O’Brien.

Surprisingly, despite the fact that most organic remains vanish in an archaeological record, the practice of archaeology has many botanical dimensions. The Penn Museum is highlighting three main areas—archaeobotany, ethnobotany, and ethnographic plant-based material culture—in our Year of Botany at Ban Chiang, a UNESCO World Heritage Site excavated by the Museum from 1974 to 1975.

Foremost among these dimensions is archaeobotany and its important focus on studying ancient seeds (called “macrobotanical remains”) recovered during excavations. Specialists study those remains, and in 2024, the Penn Museum’s Ban Chiang Project was able to bring archaeobotanist Dr. Cristina Castillo from University College London to the Museum to conduct “flotation” of bags of dirt that had lived in the Penn Museum subbasement since almost 40 years ago.

As the Director of the Ban Chiang Project at Penn, I have been a “mother hen” to those bags over the decades, preserving them for the opportunity for just such a study.

Two people sit on a deck outdoors in Southeast Asia, looking through plant and seed samples — The author, left, in 1981 collecting the Thai plant specimens from the Ban Chiang region that are now being studied at the Penn Museum. She worked closely with Li Hirionatha, a resident of Ban Chiang village, in documenting local wisdom about the collection. Seeds in the collection can be used to compare with ancient seeds recovered from archaeological sites.

Three researchers look at fossils and taking pictures — Year of Botany team members: Dr. Varangrat Nguanchoo of the Phetchaburi Rajabhat University in Thailand, Thitipha Kuttawas from Mahidol University in Thailand, and Steve Lang, the Keeper of the Asian Collection at the Penn Museum. The team is seen visiting the Academy of Natural Sciences, a key institutional collaborator for the program. Here they visit the plant fossil room at the Academy, but the age of these specimens is much older than the Ban Chiang specimens.

Archaeobotanists are few and far between, particularly for Southeast Asia, where archaeological research is still somewhat nascent. Therefore, one objective of the Year of Botany has been to train Thai botany students from Mahidol University in Bangkok in the extraction technique of flotation.

The flotation variant often used with tropical soils is bucket flotation, where sediments are massaged in buckets of water to release charred bits such as charred seeds. Buckets of water with the massaged sediments are carefully emptied into cloth sieves to catch the organic bits which have floated to the surface of the water.

The organic materials caught, called “flot,” are dried in the sieves, and the dried flot is bagged to be sent to the laboratory. The rest of the sediment is sieved (called wet sieved) in a brass mesh, spread out, and other bits of interesting finds are removed, things like fish bone, beads, sherds, and so forth. Dr. Castillo and team floated more than 90 bags of sediments over 10 days in a courtyard at Penn Museum. After cataloging the bags of flot, they were mailed to Dr. Castillo’s laboratory in London.

A researcher sorts through soil samples outside the Penn Museum — Kittiyaporn Sukprasong was one of the students in the Plant Science Department of Mahidol University, Bangkok, who trained in the archaeobotanical extraction technique called “bucket flotation.” She is massaging in the water in the bucket sediment excavated from Ban Chiang about 50 years ago. The material that floats will be poured into the mesh-lined receptacle on the right.

A closeup of a bucket as a researcher sorts through soil samples outside the Penn Museum — Kittiyaporn Sukprasong was one of the students in the Plant Science Department of Mahidol University, Bangkok, who trained in the archaeobotanical extraction technique called “bucket flotation.” She is massaging in the water in the bucket sediment excavated from Ban Chiang about 50 years ago. The material that floats will be poured into the mesh-lined receptacle on the right.

Microscopic study of the flot allows the archaeobotanist to separate seeds from remains like rootlets and wood charcoal. Many seeds can be identified to species, such as Oryza sativa or rice. Even weed seeds can be identified and these can help reconstruct cropping techniques.

The Ban Chiang Project will post additional stories on the Penn Museum Voices blog on other aspects of their Year of Botany in the coming months.

Joyce White is the Director of the Middle Mekong Archaeological Project at Penn Museum and an Adjunct Professor in the Department of Anthropology.

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