Phytoliths in dicotyledons occurring in Northwest Europe: establishing a baseline

The absence of a modern plant-based 'dicotyledon' phytolith reference baseline impedes the accurate interpretation of fossil phytolith records in archaeological and palaeoecological research within Northwest (NW) Europe. This study aims to fill this gap by documenting and analysing the phytolith record from modern dicotyledon taxa occurring in this region.

Phytoliths were extracted from several plant parts of 117 plant specimens representing 74 species (one or two specimens per species). The study employed light microscopy to examine phytolith production (non-producer, trace, common or abundant) and phytolith assemblage composition. The data were analysed statistically to (1) determine the influence of taxonomy and plant part on phytolith presence (absent/present) using a mixed model, (2) assess phytolith assemblage variation using a permutational multivariate analysis of variance (PerMANOVA) and (3) identify patterns among sample groups including segregation for plant part, life form (forbs vs. shrubs/trees) and order using linear discriminant analyses (LDA).

Morphotype analysis revealed diagnostic morphotypes and features for specific plant families, genera and plant parts. LDA effectively segregated plant parts and life forms, though taxonomic groupings showed limited segregation. Phytolith presence (absent/present) was found to vary, influenced by both plant part and taxonomy. For species examined through two specimens, although phytolith production varied considerably, phytolith assemblage composition was consistent.

This study establishes a 'dicotyledon' phytolith baseline for NW Europe, showing that the phytolith record can be informative in terms of plant part and life form and that several phytolith morphotypes and/or features are taxonomically diagnostic below 'dicotyledon' level. The findings constitute a foundation upon which future research can build, refining and expanding our knowledge of the NW European region.