Introduction

Plant finds from archaeological sites can, in most cases, be determined to the species level but rarely to the level of infraspecific groups with specific features. Flax (Linum usitatissimum L.) is one of the founder crops for agriculture in the Near East (Weiss and Zohary 2011). Flax comprises two main usage groups with distinct phenotypes: fibre flax types that produce a long, unbranched stem, and oil flax (linseed) types that produce more and larger seeds for direct consumption or oil extraction (Körber-Grohne 1987). Additionally, some flax types display an intermediate phenotype between these two extremes and may have been used for both purposes (Kulpa and Danert 1962). Taxonomists have described the diversity in flax and distinguished infraspecific groups based on research of world collections of flax in genebanks, reflecting these distinct usage groups based on seed and capsule features, among others (Helbaek 1959; Kupla and Danert 1962).

The main objective of this study is to discuss whether the archaeological flax capsules from Ancient Egypt already represent a specialised production for oil or fibre, or the intermediate type usable for both purposes. The flax capsules being examined span a wide chronological period (3000 BC-100 AD) and are part of the collection at the Botanical Museum of the Free University of Berlin. To establish a comprehensive and reliable basis for comparing capsule dimensions in archaeological findings, the measurements of the ancient samples were compared with a diverse range of flax germplasm preserved by Plant Gene Resources of Canada, located in Saskatoon, Province Saskatchewan.

State of the art and objective of the study

Archaeological findings of cultivated plants are important for understanding their evolution (Helbæk 1959). The domestication and evolution of flax, its spread from its original geographical locations of domestication, and its diverse uses still present many unanswered questions (Karg 2020). Determining the precise origins of different types of flax (fibre flax and linseed) and their primary uses in various regions continues to be a challenging task.

Flax seeds are rich in polyunsaturated fatty acids, specifically linoleic acid omega-6 (ω-6) and α-linolenic acid omega-3 (ω-3). These fatty acids are essential nutrients for humans and must be obtained through ingestion, as our bodies cannot produce them. The oil can be extracted from crushed flax seeds by boiling them in water. Once the liquid has cooled and the solid plant tissues have been removed, the oil can be separated. This extraction process has been archaeologically documented through the discovery of flax seeds in vessels dating back to the Iron Age, such as those found at the Tel Beth-Shean site in Israel, as discussed by Kislev et al. (2011) and Cassuto et al. (2022). Textiles made from flax fibres have also been found in ancient cave deposits in Nahal Hemar, Israel, dating back to the 7th millennium BC (Shamir and Rast Eicher 2020), leaving the debate open as to whether flax was first cultivated for its seed oil or fibre use. Identifying the type of flax being studied provides insight into the agricultural and economic context of archaeological findings.

Currently, biometric research of ancient flax seeds appears to be a suitable method for distinguishing different types of flax (Herbig and Maier 2011; Karg et al. 2018). In Central Europe, there was a clear change in seed size during the 4th/3rd millennium BC, with smaller seeds replacing the larger ones found in earlier deposits. The larger-seeded flax in that region is believed to have been used for its oil, while the smaller-seeded flax was used for textile production. This is supported by a contemporaneous increase in textiles made from flax fibres and the presence of numerous textile tools in the archaeological record of this region (Rast-Eicher and Dietrich 2015; Karg 2022).

Renowned for its linen production, Ancient Egypt had a rich history of cultivating, utilizing, and trading fibre flax (Vigo 2010). This is well-documented through the discovery of textiles, such as the use of flax bandages to wrap mummies (Heer 1872; Herzog 1929). Flax has been used for textile production since at least the Neolithic period. The oldest evidence of flax textiles in Ancient Egypt comes from the Fayyum site A and dates back to 5000 BC (Jones and Oldfield 2006). Other early textile findings belong to the Badarian period (4400–3800 BC), when linen textiles were used in burials, as well as for mats and skin clothing (Brunton and Caton-Thompson 1928, 19). From the Predynastic period (3800–3100 BC) onwards, linen textiles were commonly found in burials, often used to cover the body and also offered as grave gifts (Jones 2008). During the early Pharaonic period (3100–2100 BC), there was a highly developed technical production of high-quality textiles and fine yarns, including the production of “ultra-fine yarn” (Cooke and Gamal 1990).

Other evidence supports the extensive use of flax for fibre purposes. Wall paintings in the tombs of Sennedjem (TT1) and Ipuy (TT217) in Deir-el Medina in Thebes, dating back to the beginning of the 19th dynasty (thirteenth century BC), depict tall-growing flax that appears to have been harvested while still green. This suggests that flax cultivated for fibre use is being portrayed. On the other hand, proving the use of flax for oil production is considerably more challenging.

Unfortunately, detailed documentation of archaeo-botanical remains is rarely available for excavations on Egyptian sites. However, a recent study by Karg et al. (2018) has presented findings on a selection of Ancient Egyptian flax seeds. In this study, they compared seeds of the wild progenitor of cultivated flax, pale flax (Linum bienne Mill.), with seeds of cultivated flax. The dry climate of Egypt has played a crucial role in preserving not only the flax seeds but also the capsules. This preservation allows for the expansion of the application of a multidisciplinary methodology to analyse ancient plant material and gain insights into the evolution of flax in Ancient Egypt.

Material and methods

Desiccated preserved flax remains from Egyptian sites dating from the 3rd millennium BC to the second century AD (Fig. 1 and Table 1) that were collected at the end of the nineteenth century by Georg Schweinfurth, a German pioneer of archaeobotany and textile archaeology (Finneiser et al 2010; Fig. 2) were used for this study.

Fig. 1
figure 1

Map with the Egyptian sites described in the text

Table 1 Egyptian sites with flax capsule findings. Characterization and measurements of the capsules
Fig. 2
figure 2

Nicely decorated show box with flax capsules from collection Schweinfurth (SSchw166) with label handwritten by Schweinfurth. Linum usitatissimum L. gefunden zu Schech Abd el Qurneh, Theben, in einem Grabe der XX Dynastie, das als Speicher diente dessen Inhalt in Vergessenheit gerieth. Man fand daselbst 1885 Ardeb Maspero. Linum usitatissimum L. found in a grave at Schech Abd-el-Querneh, Theben, in a grave of the XX dynasty that was used as a granary but its content fall into oblivion. Found in 1885 by Ardeb Maspero

The flax capsules were measured with an Olympus SZX16 DP72 stereo microscope and by using an image analysis program. In Table 1 the identification code (ID), the dating of the Egyptian desiccated capsules, the number of measured capsules and the means of the measurements are listed.

In Appendix 1 all the samples are listed and, when possible, recontextualized.

Genebanks as reservoirs of the genetic diversity of cultivated plants offer excellent opportunities to assess the archaeological findings of remains of cultivated plants for identification. The great gene-bank pioneer and crop plant researcher N.I. Vavilov pointed already out that crop plants are documents of greatest relevance for historical research, similar to archaeological artefacts (Vavilov 1926).

The flax collection at the Canadian National genebank (PGRC) is a world collection and covers the entire range of diversity in the species and includes many ancient landraces. The characterization data was generated during field trials planted from 1998 to 2008 at Saskatoon (Diederichsen et al. 2013). Based on comprehensive characterization, the classification into fibre flax, oil flax and intermediate flax according to Kulpa and Danert (1962) was conducted for all accessions (Diederichsen 2009). Measurements of recently grown flax of 2926 genebank accessions maintained by PGRC were considered. The raw data from the publication Diederichsen (2009) was used and we present here an analysis focusing on the capsule measurements. For measuring the width of the mature capsules, the measurements were done by passing the mature capsules through holes of defined diameter in a metal plate to determine in which of nine classes ranging from 5.6 to 9.1 mm the capsules fall. Ten capsules were assessed for each accession and the modal value was recorded. Capsule width was assessed for 2926 accessions.

It is possible to distinguish modern flax capsules from the different usage groups for oil and for fibre, as they differ in size (Diederichsen and Richards 2003).

The degree of the spontaneous opening of the mature capsules (dehiscence) allow to categorize the accessions into various groups. Data on dehiscence was collected from 2931 accessions. A rating scale was applied on ten capsules and the modal value was recorded.

The data collected on completely dehiscent flax accessions was eliminated from the PGRC collection because completely dehiscent capsules were not found in the ancient material.

Results

Table 2 shows that modern fibre flax accessions have a higher proportion of capsules rated as notably to slightly dehiscent compared to indehiscent. In typical oil flax, the capsules tend to be only very slightly dehiscent. Intermediate flax mostly has slightly dehiscent capsules.

Table 2 Dehiscence of mature capsule in genebank material

Table 3 displays the width measurements of flax capsules from the accessions at PGRC. A clear distinction is observed, as fibre flax has narrower capsules compared to oil flax. However, intermediate types also generally have narrower capsules. Figure 3 extracts the capsule width distributions for fibre flax and oil flax from Table 3, allowing for a better comparison of the two extreme groups.

Table 3 Capsule width of modern flax accessions
Fig. 3
figure 3

Capsule width distribution in modern gene-bank accessions of fibre flax (n = 394) and oil flax (n = 172)

Table 1 lists the measurements of ancient flax capsules from Egypt. A total of 88 capsules from the Schweinfurth collection were measured and categorized following the capsule dehiscence scheme in Diederichsen and Richard (2003). Of these, only 4 were categorized as “more slightely dehiscent”. These are the oldest capsules, dating back to the 3rd millennium BC, found at the site of Abusir el-Meleq in Northern Egypt (SSchw169; Figs. 4a, b). The four capsules are more slightly dehiscent (a bit open), rather small in size, and interpreted as belonging to a fibre flax variety. The capsules clearly show 10 segments, indicating that each capsule originally contained up to 10 seeds. Flax capsules from the 3rd millennium BC were also found at the site of Abusir (SSchw388), but they were fragmented and could not be measured (Table 1).

Fig. 4
figure 4

a, b Egyptian flax capsules from the Schweinfurth collection (SSchw169)

Most capsules dating to the 2nd millennium BC appear indehiscent (closed) and larger in size compared to those from Abusir el-Meleq (SSchw169). They are therefore interpreted as belonging to an oil flax (linseed) type (SSchw165, SSchw171, SSchw170). The measurements of 20 capsules from the site of Sheikh Abd el-Qurna (SSchw166) do not clearly indicate a fibre flax type (Table 1 and Fig. 5a, b), and are thus characterized as an intermediate flax type (fibre/oil). The same observations apply to the capsules from the site of Assasif, dating to the 2nd-1st millennium BC (SSchw164): the capsules are quite large and slightly open, indicating an intermediate flax type used for both fibre and oil production. The more recent flax capsules from the site of Abusir el-Meleq (SSchw167), dating to the second century AD, are large and closed, clearly indicating a seed/oil usage type of flax plant.

Fig. 5
figure 5

a, b Egyptian flax capsules from the Schweinfurth collection (SSchw166)

Discussion and conclusions

For the first time, desiccated flax capsules from ancient Egyptian sites were studied and compared with measurements and morphological features of modern genebank material. The comparisons show that the oldest flax finds, dated to the 3rd millennium BC, were probably fibre flax types. In all later periods, an intermediate flax and/or oil type was in use, as supported by a previous study on Egyptian flax seeds (Karg et al. 2018). This result is intriguing and clearly indicates that fibre flax was already being used in the early Pharaonic history.

Most of the later flax findings originated from the Theban region and indicate its use for seed production. However, the Theban region may not have been the most suitable for cultivating fibre flax compared to the Delta, which had better access to water for achieving higher fibre yield and quality. The humid conditions in the delta environment have caused the destruction of ancient organic materials, including flax capsules, limiting archaeological findings to more arid areas.

Considering these challenges and the limited number of samples in this study, future investigations could explore the following questions: is there a distinct shift between the third millennium and the second millennium, with flax production leaning more towards the use of intermediate flax rather than the typical fibre flax used in the previous period? Alternatively, could there have been a regional differentiation, with fibre flax cultivation primarily occurring in wetland areas such as the delta, while the more arid southern area like Thebes focused on the cultivation of linseed flax? Did climate change during the second millennium BC create better conditions for the cultivation of an oil flax type? Was linseed oil in higher demand for food or for the embalming process of the dead, leading to more frequent use of this flax type as a grave gift? If a distinct type of flax for fibres was already available in the 3rd millennium BC, when did the selection and differentiation process start (or arrive) in Ancient Egypt?

Through this multidisciplinary study, we aim to demonstrate the possibility of uncovering answers to the question of whether ancient cultures intentionally selected and cultivated specific crop types for particular purposes. We suggest that the characterization data of genebank accessions should be utilized more frequently to shed light on the ancient history and evolution of cultivated plants.