Stone Fruit Identification in Archaeological Contexts (Part 1)

By Aubree Marshall and Benjamin Akey

Sometimes, when archaeologists are lucky, we run into botanical remains. In my personal research, I look at microbotanicals (like pollen, starches, and phytoliths) from dental calculus (the stuff your dental hygienist scrapes off of your teeth!) to understand diet. Because calculus fossilizes during a person’s life, it provides a unique view into what a person was interacting with. But this isn’t the only way that archaeologists study botanical remains. Sometimes we run into macrobotanicals, or plant remains that you can see without a microscope. A prime example of this is stone fruit seeds! 

Stone fruits come from deciduous trees originally belonging to temperate zones (Elleuch and Hamdi, 2024). Some examples of stone fruits include peaches, nectarines, plums, apricots, cherries, and mangos (Maringgal et al., 2020). There are three distinct parts, including the flesh (exocarp and mesocarp), the seed, and the woody endocarp (the portion encompassing the seed) (Figure 1, Famiani et al., 2020). Many people may confuse the endocarp with the seed, but we have to be careful not to conflate them when trying to make an identification. This can lead to misidentification of the fruit in question. Further, knowing the difference between endocarps from stone fruits versus other drupes, like walnuts, is integral to understanding what types of food sources people may have been interacting with in the past. 

CAP found two examples of stone fruit endocarps during the 2024 field season in our Spartan Solar project. Spartan Solar, which you can read a little bit more about here, is an ongoing project we initially started in response to plans to construct a solar farm in the south-eastern reaches of campus (now cancelled). This section of campus currently hosts several agricultural research and teaching facilities, as well as a number of pastures for bovine and ovine livestock on campus. 

While preparing to do fieldwork in the vicinity, CAP identified a series of eight late-19th to mid-twentieth farmsteads overlapping with the project’s boundaries (Akey 2022). Our efforts to survey and excavate these small family run farms have revealed several middens composed of materials dating to the mid-twentieth century, shortly before the university purchased the land parcels to expand their operations. In some cases, these features may be related to the process of the university clearing out and demolishing extant structures on the property, which can be seen in contemporaneous aerial photographs of the area. It is from one of these contexts–filled with concrete debris, ferrous structural fasteners, hooks, and chainlink fragments, as well as a variety of fragmented glass and ceramic containers–that the stone fruit endocarps were recovered.

One of the endocarps was wholly intact (Figure 2), while one was broken open (Figures 3 and 4) – the latter seemed to have the seed previously removed. Given that stone fruit seeds are rarely eaten by humans due to the high cyanide content, the cracked example with the missing seed may represent the foraging activity of rodents or other animals. 

While looking over the endocarps and comparing them to the reference photo in Figure 5, we identified several surface features that were noted. For example, both endocarp examples have the apiculate apex present, as well as grooves, pits, and both longitudinal and transverse furrows. After we identified the surface features, we then compared our specimen to published examples of drupe endocarps (Figure 6). The presence of the surface features labeled above (apiculate apex, grooves, pits, longitudinal and transverse furrows) and the size of the specimen ruled out several similar stone fruits such as cherries, apricots, and plums. While other drupes have pretty similar endocarps, after comparing the CAP endocarps to other reference samples, I believe that our endocarps most likely represent a specimen of Prunus persica – the species that comprises both peaches and nectarines. Due to the common peach and nectarines representing different cultivars of the same species, it is difficult to make a further determination as to which is represented within the Spartan Solar Collection.

In the context in which we found these endocarps, this process of identification provides some information related to possible subsistence and/or production patterns at the site. Aerial photography of the site (Figure 7) from 1938 and 1950 shows the presence of a large orchard directly north of the area we shovel-tested and excavated in 2024. For some past farmstead research, CAP has been able to use the U.S. Census ‘agricultural schedules’ to identify what products were produced at such sites, but these records are typically only available for the latter 19th-century (see Janesko 2018 for an example of how agricultural schedules can be used in archival phases of archaeological research). In absence of detailed records on what the farmstead would have been producing in the mid-20th century, these peach/nectarine pits may provide an indicator that part of the orchard was dedicated to stone fruit production, which is further bolstered by the fact that some varieties of peaches and nectarines grow well in the local climate (USDA Hardiness Zone 6a).

In the midst of searching for reference collections, we decided that it might be helpful to create a reference collection of our own for quick identification of stone fruit pits and other drupes. Due to the seasonal availability of certain drupes such as cherries and apricots, we decided to hold off including this process in this blogpost, and to split this idea off into a new blogpost later this semester – stay tuned!

References:

Akey, Benjamin (2022). Solar Project 2022 – Historical Background Research. Report prepared for the Campus Archaeology Program, Michigan State University, Lansing, Mi.

Dal Martello, R., M von Baeyer, M Hudson, R.G. Bjorn, C. Leipe, B Zach, B Mir-Makhamad, T.N. Billings, I.M. Muñoz Fernández, B. Huber … R.N. Spengler (2023). Domestication and Dispersal of Large-Fruiting Prunus spp.: A Metadata Analysis of Archaeobotanical Material. Agronomy 13(1027). https://doi.org/ 10.3390/agronomy13041027 

Elleauch, Amine and Imen Hamdi (2024). Naturally occurring viroid diseases of economically important plants in Aftrica. In Fundamentals of Viroid Biology. Eds C.R. Adkar-Purushothama, T. Sano, J.P. Perreault, S.M. Yanjarappa, F. Di Serio, J.A. Daròs. Academic Press, pp. 133-150. https://doi.org/10.1016/B978-0-323-99688-4.00013-4.

Famiani F, Bonghi C, Chen Z-H, Drincovich MF, Farinelli D, Lara MV, Proietti S, Rosati A, Vizzotto G and Walker RP (2020) Stone Fruits: Growth and Nitrogen and Organic Acid Metabolism in the Fruits and Seeds—A Review. Plant Sci. 11:572601. doi: 10.3389/fpls.2020.57260. 

Maringgal, Bernard, Norhashila Hashim, Intan Syafinaz Mohamed Amin Tawakkal, and Mahmud Tengku Muda Mohamed (2020). Recent advance in edible coating and its effect on fresh/fresh-cut fruits quality. Trends in Food Science & Technology, 96 (253-267). https://doi.org/10.1016/j.tifs.2019.12.024. 

Petre, A. (2023). 10 Surprising Health Benefits and Uses of Peaches. Healthline. https://www.healthline.com/nutrition/peach-fruit-benefits 
Su, T., P. Wilf, Y. Huang, S. Zhang, and Z. Zhou. 2015. Peaches preceded humans: Fossil evidence from SW China. Scientific Reports 5: 16794. https://doi.org/10.1038/srep16794