Phytolith characterization of culturally salient plant species of the Pacific Northwest of North America

Palaeoecological and archaeological studies often use soil phytoliths to gain insight into past vegetation changes and the long-term use of plants by people, particularly domesticated cultivars. However, to make accurate interpretations and analyses using plant phytoliths, regionally-specific reference collections are warranted. There is ample research documenting phytolith morphotypes observed in grass species worldwide (due to their high phytolith production), and of dicots in tropical regions, but there is dearth of phytolith references for dicot species in temperate regions like the Pacific Northwest of North America. This study aims to fill part of this gap by documenting phytolith morphotypes observed in 60 culturally important plant foods, medicines, and textiles, all predominantly dicot species. Phytoliths are classified by abundance in specific plant parts (e.g., stem, leaf, flower) and the findings are compared to closely related species studied elsewhere. Results indicate that many of the dicot plant species in the Pacific Northwest produce more phytoliths than closely related species worldwide, likely due to differing environmental factors which affect phytolith production in plants. These findings could be useful in palaeoecological contexts to assess vegetation changes or identify dicot-dominated ecosystems, like Indigenous cultivated and managed forests and other perennial fruit tree/shrub dominated landscapes. Additionally, three of the species studied here showed possible diagnostic phytoliths but further confirmation is warranted. Future studies should consider localized environmental patterns affecting phytolith production, and therefore, our understanding of phytolith taxonomy and deposition/taphonomy.