Phase 2 plant macrofossil assemblage

Plant macrofossil remains were recovered from all phases of occupation at the site using flotation (see Methods). The Phase 2 assemblage includes over 1000 non-wood plant macrofossils from a distinct hearth feature (C1/43 A) and excavated sediment matrix (see Supplementary Table 1). These macrofossils can be broadly categorised into four distinct groups: (i) endocarp and mesocarp (‘nutshell’ or ‘fruit-stone’) from a variety of fruit and nut producing species; (ii) vegetative parenchyma from USOs (‘roots and tubers’); (iii) stem tissue from the Arecaceae (palm) family and (iv) various other fragments of plant material. Within these groups, genus-, or species-specific identifications have been made for five taxa, with a further five types identified to broader botanical categories.

The paucity of charcoal prior to human occupation (Supplementary Fig. 2a) and the presence of a diversity of edible species preserved by burning suggests that the assemblage was largely derived from human activities, specifically the cooking and disposal of plant resources in hearths. This is corroborated by the relatively high percentage (17%) of fragile parenchymatous tissue from USOs preserved in the assemblage. USO-producing species have evolved to survive and profit from bushfires, rapidly regenerating new aerial shoots from their buried vegetative organs28. These organs, themselves, are therefore unlikely to have been charred within the site without human activity. However, this does not preclude the inclusion of some of the Phase 2 plant macrofossils via non-human agents.

Endocarp and mesocarp

Charred endocarps of five fruit and nut taxa were identified: Buchanania sp.; Canarium australianum; polydrupe Pandanus sp.; Persoonia falcata; and Terminalia sp. (Fig. 2). All of these taxa are common in open forest and woodland, and/or monsoon vine forest environments29, and the majority require little or no processing. Today, the abundant and easily harvested ‘plums’ of Buchanania spp. and Persoonia falcata are highly sought after. The fruits can be eaten raw but are also often ground into a paste, incorporating the endocarp and seed, prior to consumption (MN, DjDj). Canarium australianum is a relative of the widely used Melanesian tree-crop, galip (C. indicum), and has a small oil-rich kernel (<1 cm) that is easily extracted with a single blow from a hammerstone (DjDj). A number of Terminalia species are edible, consumed either as fruits (T. carpentariae, T. erythrocarpa, T. ferdinandiana, T. microcarpa) or easily-extracted nuts (T. grandiflora; MN, DjDj)30. However, there are also a number of non-edible species of Terminalia in the Northern Territory.

Fig. 2: Examples of endocarp from Phase 2. a, b Buchanania sp. endocarp from C2/46(HR), a scale bar is 1 mm, b transverse section, scale bar is 500 µm; c Canarium australianum endocarp from C2/38(HR), scale bar is 500 µm; d C. australianum endocarp from C2/37(HR), close-up of internal surface, scale bar is 500 µm; e Polydrupe Pandanus sp. endocarp from C2/42(HR), transverse section, scale bar is 500 µm; f P. spiralis mesocarp from C2/37, scale bar is 200 µm; g, h Persoonia falcata endocarp from C2/37(HR), g scale bar is 1 mm, h close-up of internal surface, scale bar is 200 µm; i, j Terminalia sp. endocarp from C2/37(HR), i scale bar is 1 mm, j transverse section, scale bar is 200 µm. See the supporting online information and Supplementary Figs. 3-7 for detailed identification proofs and the corresponding reference materials. sl seed locule, vb vascular bundle, fb fibrous bundle. Full size image

Pandanus formed a substantial element of the early colonial diet of Indigenous Australians in Arnhem Land and is also a valuable material in weaving and fibrecraft31. There are two types of polydrupe pandanus in Arnhem Land: P. spiralis and P. basedowii29. Only one fragment from Phase 2 at Madjedbebe, a portion of mesocarp, can be securely identified as P. spiralis (Fig. 3f). However, it is likely that the majority come from this species, since P. basedowii only grow on the escarpment top and would have been difficult to access from Madjedbebe (see Fig. 1b). Extracting kernels from the fibrous and mechanically-resistant prismatic structure of the P. spiralis drupe is a labour-intensive process when using stone tools. The explorer, Ludwig Leichardt, recorded Indigenous groups in the Gulf of Carpentaria in the 1840s using “large flat stones and pebbles” to bash apart the drupes32. However, once open, the small kernels are rich in fat (44–50%) and protein (20–34%)33.

Fig. 3: Examples of vegetative parenchyma from Phase 2. a, b Monocotyledonous stem-based storage organ Type A from C2/41; a depicting skin-patterning and root abscission scar, scale bar is 500 µm; b close-up of root abscission scar, scale bar is 100 µm; c transverse section of monocotyledonous stem-based storage organ Type A from C2/32 A, depicting an endodermis and a series of closed collateral vascular bundles, arrows point to phytoliths on edges of vascular bundles, scale bar is 500 µm; d MN peeling a ‘hairy’ Dioscorea bulbifera tuber beside a hearth built to cook it, photo taken by SAF; e, f longitudinal section of monocotyledonous stem-based storage organ Type B; e scale bar is 300 µm; f close-up of vascular bundle, scale bar is 20 µm; g, h transverse section of secondary-root storage organ Type A from C2/39 A; g scale bar is 2 mm; h close-up of central tract of xylem, scale bar is 500 µm. ra root abscission scar, en endodermis, vb vascular bundle, ph phloem, xy xylem. Full size image

Vegetative parenchyma

Three distinct types of vegetative parenchyma are present in the Phase 2 assemblage. These include parenchymatous tissue from two types of monocotyledonous, stem-based storage organs and a fragment from a secondary-root storage organ (Fig. 3). Monocotyledonous stem-based storage organ Type A is represented in Phase 2 only by charred fragments of its skin tissue, which have distinct root abscission scars, or ‘eyes’, and surface patterning (Fig. 3a, b). These fragments are comparable to charred peelings generated by contemporary Indigenous Australians when they remove the coarse external surface of cooked USOs before consumption, often in proximity to the hearth in which they were cooked (MN, DjDj; Fig. 3d). The presence of an endodermis, in a larger fragment of this type recovered from Phase 3, allows for its further identification as an aquatic or semi-aquatic USO (Fig. 3c). Endodermis is rarely present in stem tissue, except in aquatic plants where they are significant in controlling water balance within perennating stems34.

Arecaceae

There are two types of Arecaceae stem tissue present in the Phase 2 assemblage (Fig. 4). Type A, characterised by the presence of mostly two or more metaxylem elements per fibrovascular bundle, has a similar anatomy to that of Livistona spp. palm tissue. Type B, represented largely by the peripheral section of the palm stem, is characterised by the presence of only one metaxylem element per fibrovascular bundle. Type B is only found in the Phase 2 assemblage and may represent the peripheral xylem of Type A or another taxon of the Arecaceae. The apex, or ‘heart’, and pith, or whole young stem, of several palms present in open woodland and monsoon vine forest environments in western Arnhem Land can be consumed (apex: Carpentaria acuminata, Hydriastele ramsayi; apex and pith: L. benthamii, L. humilis and L. inermis)30,35. While the apex of these palms may be eaten raw or lightly roasted, the pith requires roasting for an extended period (~12 h) prior to pounding. This process removes the most fibrous elements from the otherwise starchy pith, making the carbohydrates within the pith readily available for consumption. While there are no distinguishing apical features on the fragments of stem from the Phase 2 assemblage, their size makes it impossible to securely identify them as basal (pith) stem.