Morphological diversity of bulliform cell phytoliths derived from 67 species and 22 other taxa of 36 genera in 10 tribes and 6 subfamilies of Poaceae was studied using light and scanning electron microscopy. Bulliform cell phytoliths were polyhedron constitutings with six faces, one top, one bottom, two end profiles, and two laterals. The end profile morphology varied widely from asymmetrical to symmetrical through triangular, rectangular, and round and had three characteristic features in the presence of protuberance at boundary and the outlines at top and bottom sides in the end profiles. The outlines at the top and bottom sides of the end profiles were classified into five types, rotundate convex, squarish, thicker towards the end, sunken, and with protuberances, and six types, rotundate convex, acute convex, flat, with one sunken place, with two sunken places, with three sunken places, respectively. The surfaces of bulliform cell phytoliths had protuberances and sculptural patterns. The sculptural pattern, observed only on the bottom surfaces, was classified into two main types, reticular and striped, and two subtypes, diamond shaped and latticed. The protuberances were classified into five types, nailhead-shaped, trapezoid, clavate–shaped, forked, and verruca.
Starch residue analysis can explore the past vegetation and plant utilization through extracting starch grains from archaeological sediments and artefacts. Its applicability to Japanese archaeology was demonstrated recently, and a modern starch reference collection has been established for taxonomic identification of starch grains. After reviewing research trends outside and inside Japan, this study shows morphological features of starch grains for specifying plants used in early Japan and presents methodology for comparative approaches to archaeological sites. The microscopic observation of starch grains from 17 plant species, thought to be typical food plants between the Palaeolithic and Yayoi periods, showed that starch grains from Colocasia esculenta, Dioscorea japonica, Juglans ailanthifolia var. sieboldiana, Echinochloa esculenta, Oryza sativa, Panicum miliaceum, and Setaria italica can be differentiated by their morphological attributes, but that starch grains of Quercus serrata are morphologically similar to those of Quercus acutissima. Against models presented by some researchers for specifying plants used in sites, the morphological classification of starch grains in this study showed that archaeological starch grains need to be identified more strictly. The present classification of starch grains can identify more than one species processed by archaeological artefacts and clarify plant food processing in early Japan.