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Acknowledgements IE has received funding from the postdoctoral fellowship programme Beatriu de Pinós (2019 BP00247), funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Marie Skłodowska-Curie grant agreement No. 801370. Laboratory materials for sample processing at the University of Barcelona were funded by the Ministerio de Ciencia e Innovaci on - PID 2020-119773 GB-I00. Visit to the site for sampling collection for this study was sponsored by a NRF Y-Rated Research Grant (No. 116358) to DS. PdlP was supported by a Poroulis grant through Cambridge University. PdlP thanks the action PID 2019- 1049449 GB-I00 funded by Spanish FEDER/Ministry of Science and Innovation. LB was funded by a National Geographic Explorer grant (NGS-54810R-19), DSI-NRF Centre of Excellence in Palaeosciences (Genus) grant (CEOOP 2020-1), and NRF African Origins Platform grant (No. 98824). Research by FdE is funded by the Research Council of Norway (SFF Centre for Early Sapiens Behaviour- SapienCE-project 262618), the Talents program of the University of Bordeaux (n. 191022_001), and the program “Human Past”, funded by the same university.We are grateful to Amafa for issuing us with the excavation permit (SAH 15/7645), and to SAHRA for an export permit (CaseID 15987).We thank two anonymous reviewers for their helpful comments that significantly improved the manuscript., Supplementary data to this article can be found online at https://doi.org/10.1016/j.quascirev.2022.107898., Border Cave is a well-known South African Middle and Early Later Stone Age site located in KwaZulu-Natal. The site has exceptional plant preservation, unparalleled in the African Middle Stone Age archaeological record. This study focuses on the phytolith and FTIR analysis of two Members (2 BS and 2 WA) of the under-documented post-Howiesons Poort occupations dating to ∼60 ka. These members contain complex successions of vertically overlapping, interdigitating light brown sediments, plant bedding and combustion features of various sizes. The complexity and distinctiveness of these deposits provide an excellent opportunity for the study of plant exploitation strategies and their associated human behaviour. Our taphonomic assessment inferred, through the variability of phytolith properties and minerals composing archaeological layers, that specific occupations suffered more physical weathering than others, for example in the form of trampling. The preservation of fragile and highly soluble phytoliths (eudicot leaf phytoliths) and the high frequencies of articulated phytoliths indicates that some bedding deposits experienced little disturbance after their deposition. Not all bedding layers dating to ⁓60 ka show, from a phytolith perspective, the same plant composition, which could be explained in terms of changes in human preference for the use of plants over time to construct bedding or because distinct types of living floors are represented. Finally, the systematic application of phytoliths and FTIR to the complex archaeological sequence of Border Cave confirm these analyses can be used in the future to identify bedding deposits not visible to the naked eye, and behavioural patterns obscured by diagenetic or biased processes during sampling., Programme Beatriu de Pinós (2019 BP00247), funded by the Secretary of Universities and Research (Government of Catalonia), Horizon 2020 programme of research and innovation of the European Union under the Marie Skłodowska-Curie grant agreement No. 801370, Ministerio de Ciencia e Innovación - PID 2020-119773 GB-I00, NRF Y-Rated Research Grant (No. 116358), Action PID 2019- 1049449 GB-I00 funded by Spanish FEDER/Ministry of Science and Innovation, National Geographic Explorer grant (NGS-54810R-19), DSI-NRF Centre of Excellence in Palaeosciences (Genus) grant (CEOOP 2020-1), NRF African Origins Platform grant (No. 98824), Research Council of Norway (SFF Centre for Early Sapiens Behaviour- SapienCE-project 262618), Talents program of the University of Bordeaux (n. 191022_001), Program “Human Past” University of Bordeaux, SAH 15/7645, CaseID 15987

Early plant use is seldom described in the archaeological record because of poor preservation. We report the discovery of grass bedding used to create comfortable areas for sleeping and working by people who lived in Border Cave at least 200,000 years ago. Sheaves of grass belonging to the broad-leafed Panicoideae subfamily were placed near the back of the cave on ash layers that were often remnants of bedding burned for site maintenance. This strategy is one forerunner of more-complex behavior that is archaeologically discernible from ~100,000 years ago.

Extraordinary preservation of plant remains provides an insight into the construction and materials of bedding at Border Cave, South Africa. Towards the back of the cave there are particularly thick layers of desiccated and charred grass and our botanical study is from bulk samples of these approximately 60,000 to 40,000 year-old layers (Members 3 BS, 2 WA, 2 BS and 1 BS Lower C). More than one type of panicoid grass was identified, sedge nutlets were present in the older layers and in Member 2 WA particularly, eudicotyledon leaves were preserved. Plant bedding construction may have altered slightly over time with the use of sedges decreasing in favour of grass. A small item that appears to be woven monocotyledon leaf blades was recovered from Member 1 BS Lower C (42,600 years old), potentially making it the oldest evidence of simple weaving. The bedding is generally desiccated rather than burned, and often lies on an ash base. It is possible that the site's occupants burned old bedding to provide an ash base for fresh bedding. The unique preservation of desiccated plant material from as early as 60,000 years ago may in part be due to these ashy surfaces.

Using fire experiments, we investigate claims that black organic residues on lithics found in Stone Age sites are markers for heat treatment of rocks in the embers of aboveground wood fires. We buried sedges overlain with lithics and bone to replicate plant bedding sometimes found in archaeological sites. Small fires were lit over the material buried under a mixture of coarse- and medium-grained sand. Black carbonised residues formed on several lithics that were in direct contact with buried sedges that burned below the fire. FTIR, Raman and preliminary GC–MS measurements were made on dried and burnt sedge, burnt bone, and on a prominent black residue that formed on one quartz piece that had been in contact with buried fresh sedge when it was heated. Importantly, we were able to confirm the spontaneous and accidental transfer of organic compounds to lithics buried and heated underground in the presence of plant material. This means that carbonised organic residues are not useful markers for determining whether heat treatment of rocks took place above or below ground. Our preliminary experiments imply that further work should be done to investigate the causes of the residues formed on lithics underground.

We conducted experiments to compare the micromorphological signatures of modern burnt sedge and grass bedding to laminated layers of carbonized material and phytoliths in Middle Stone Age deposits at the shelter, Sibudu. The experiments were designed to clarify the formation processes associated with the laminated layers and to investigate whether these previously identified layers of bedding were deliberately burned or not. The results indicate that the laminated layers were most likely produced by human activity related to the construction, maintenance and burning of bedding. Furthermore, our experiments demonstrate that large volumes of vegetal material could have produced the relatively thin, archaeological deposits of burnt bedding.

The Middle Stone Age (MSA) is associated with early behavioral innovations, expansions of modern humans within and out of Africa, and occasional population bottlenecks. Several innovations in the MSA are seen in an archaeological sequence in the rock shelter Sibudu (South Africa). At ~77,000 years ago, people constructed plant bedding from sedges and other monocotyledons topped with aromatic leaves containing insecticidal and larvicidal chemicals. Beginning at ~73,000 years ago, bedding was burned, presumably for site maintenance. By ~58,000 years ago, bedding construction, burning, and other forms of site use and maintenance intensified, suggesting that settlement strategies changed. Behavioral differences between ~77,000 and 58,000 years ago may coincide with population fluctuations in Africa.