Palaeoethnobotany

Pal(a)eoethnobotany or Archaeobotany, "is the study of remains of plants cultivated or used by man in ancient times, which have survived in archaeological contexts". Paleoethnobotany is the archaeological sub-field that studies plant remains from archaeological sites. Basing on the recovery and identification of plant remains and the ecological and cultural information available for modern plants, the major research themes are the use of wild plants, the origins of agriculture and domestication, and the co-evolution of human-plant interactions.

Plant macrofossils are preserved through four main modes of preservation at archaeological sites. First, plant remains, usually cereal grains, chaff, seeds and charcoal are largely reduced to elemental carbon (charred) when they are heated in a reducing atmosphere. These are referred to as 'charred' or 'carbonised' plant remains. This mode of preservation is biased towards plant remains that come into contact with fire, through cooking or fuel use, and those which are less fragile, such as cereal grains and nutshell. Second, plant remains deposited in permanently waterlogged anoxic conditions are preserved as the absence of oxygen prohibits microbial activity. This mode of preservation occurs in deep archaeological features such as wells, in urban settlements where organic refuse is rapidly deposited, and at settlements adjacent to lakes or rivers. A wide range of plant remains are usually preserved, including seeds, fruit stones, nutshells, leaves, straw and other vegetative material. Third, calcium-phosphate mineralisation of plant remains occurs usually in latrine pits and in middens, as plant remains are completely replaced by calcium-phosphate. In latrine pits, plant remains which have been consumed by humans are the most common items, such as seeds of flavourings, fruit pips and fruit stones. Finally, plant remains are preserved by desiccation in arid environments, where the absence of water limits decomposition. Delicate vegetative plant remains are preserved, such as onion skin and artichoke bracts, alongside fruit stones, cereal chaff and seeds of wild plants.

Paleoethnobotanists use a variety of methods to recover and identify plant remains. Charred plant remains are usually recovered by flotation. The matrix (the soil from a suspected archaeological feature) is slowly added to agitated water. The soil, sand, and other heavy material, known as heavy fraction, will sink to the bottom. The less dense organic material such as charred seeds, grains and charcoal will tend to float to the surface. The material that floats to the top, called light fraction, is poured into a sieve (usually 250-500 µm). The light fraction is then dried and later examined under a low power microscope. Samples of the heavy fraction are also gathered for later analysis. Flotation can be undertaken manually with buckets, or by machine-assisted flotation where water is circulated through a series of tanks by a pump. Waterlogged plant remains are separated from the matrix by a combination of wet-sieving and/or small-scale flotation in a laboratory. Desiccated plant remains are usually recovered by dry-sieving, using a stack of different sieves to separate larger items such as cereal straw and fruit stones from smaller items such as weed seeds.

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