CHARRED SEEDS : IDENTIFICATION
Resources for identification
A number of manuals exist for the identification of seeds and fruits of wild species, which can be used to assist the identification of both waterlogged and charred material (see references below), and also specifically for the identification of archaeobotanical remains of certain crops species However, a modern reference collection of relevant species is an essential resource for the reliable identification of archaeobotanical remains. Manuals are useful for narrowing down the range of possible identifications and, especially for beginners, when a particular specimen is initially classified as completely unknown, manuals can be a useful way of identifying likely taxonomic groups to which it may belong. Unless the seeds of a species are particularly distinctive, however, direct comparison with modern reference material is required to take the identification further, e.g. to species level.
There are a number of ways in which a modern seed reference collection may be built up. The first is through the collection of seed in the field. Provided the person collecting the material is an experienced practitioner in taxonomic identification, this is often the most reliable method of acquiring material. It is always advisable to keep a herbarium specimen of a plant from the stand from which the seed was collected so that, if necessary, the identification can be checked at a later date. Secondly, seed may be obtained from various botanical gardens, seed banks, and other similar establishments. Experience shows that many of these suffer for a significant error rate due to misidentifications, labelling errors etc. To minimise the effects of random error, and also to encompass the range of variation between populations of the same species, a good reference collection will contain several accessions of the same species from different sources and geographic locations. A modern reference collection is far more useful to the user if it is organised according to taxonomic relationships rather then, for example, alphabetically. The former arrangement allows the user to ‘browse’ more easily for closely related taxa. Several checklists, for different geographic regions, are available for achieving such a systematic order. Seeds should be completely dry before they are stored in the collection and, provided this is requirement is met, glass vials with screw-top caps are a good vehicle for storage. Plastic should be avoided, at least for small seeds, as the static electricity they generate creates problems. For more information see Nesbitt, College, Murray (2003).
Principles of identification
When identifying archaeobotanical (or indeed other bioarchaeological) material, it is good practice to proceed by a process of elimination rather than one of simple ‘matching’. The reason for this is that many groups of closely related species have seeds which are very similar to one another, i.e. they have more shared characteristics than features which distinguish one from the other. A process of simple matching can therefore lead to mistaken identification. A better identification procedure is to list the possible candidates for the identification of the archaeological specimen (those with generally similar characteristics from the same geographical location as the specimen) and then eliminate these as far as possible on the basis of criteria which distinguish between examples of the modern candidates. Ideally, one is left with only one (or a small closely related group of) species which matches all the criteria. If the specimen is imperfectly preserved, or of the group of modern candidates cannot be distinguished, then identification must remain at that level.
For most archaeobotanical materials, identification criteria are based on gross morphological characteristics and surface patterning plus, in some cases, internal anatomy. Size is an obvious criterion, and a large difference in seed size can be a way of eliminating a candidate identification. The size of some species is highly variable, however, which underlines the importance of including a range of accessions of the same species in any reference collection, and makes size one of the least important criteria except where the difference is large. For charred material, allowance should also be made for the fact that seeds tend to shrink during charring. Colour is a useful criterion only, up to a point, for waterlogged remains.
An efficient method of identification is to construct a matrix of identification criteria for a particular group, based on modern material, to which unknown archaeological specimens can be compared rather than compare each specimen on a one-to-one basis with each modern candidate. Examples exist in the literature where such an identification ‘tool’ has been constructed for a particular group (e.g. Lange (1979) on Galium).
It must also be recognised that some species, and some plant parts, are inherently more identifiable than others; wheat glume bases and rachis fragments, for example, can be more reliably identified to species that the grains. Most archaeobotanists distinguish different levels (degrees of certainty) of identification, using ‘cf’ to indicate uncertainty of identification, and ‘either/or’ categories where closely related groups cannot be distinguished
It is sometimes best to see identification as a two-stage process: (1) identification of individual specimens within an archaeobotanical sample to a type which best fits the identification criteria; (2) on the basis of the total sample assemblage, decide which species are in fact represented in the sample. This is particularly useful where there is known overlap between the characteristics of two closely related species, as for example with the grains of emmer and spelt wheat (Jones 1998). Each grain within a sample may be classified as the ‘typical’ type for either emmer or spelt, in the knowledge that, because of the overlap in grain shape, some emmer grains may have a shape more typical of spelt and vice versa. However, taking the sample assemblage as a whole, types represented by only a few grains cannot be interpreted taxonomically, but types represented by significant numbers of grains may be taken to indicate the presence of this species. In this way it is possible to establish whether both species are present in the sample or whether there is evidence for only one species.
Seed Identification Resources
Jacomet, S. (2008) Identification of cereal remains from archaeological sites. Downloadable in English and German
- Jones, G, 1998. 'Wheat grain identification – why bother?' Environmental Archaeology 2: 29-34. (Download)
- Lange, E. (1979) 'Verkohlte Pflanzenreste aus den slawischen Siedlungsplatzen Brandenburg und Zirzow (Kz. Neubrandenburg)', pp. 191 - 207 in U. Korber-Grohne (Ed.) Festschrift Maria Hopf (Archaeo-Physika 8) Bonn. Key to Rubiaceae 'seeds', especially Galium and Asperula
- Nesbitt, M. and Greig, J. (1990) 'A Bibliography for the Archaeobotanical Identification of Seeds from Europe and the Near East', Circaea 7, 11-30. (Download)
- Nesbitt, M., College, S. and Murray, A-M. (2003)'Organisation and Management of Seed Reference Collections', Environmental Archaeology 8, pp. 77-84. (Download)