READING THE LEAVES: DEVELOPING A QUANTITATIVE APPROACH TO IMPROVE INTERPRETATION OF FOSSIL MONOCOT LEAF SYSTEMATICS AND ECOLOGY

Monocots, a group of flowering plants that includes grasses (Poaceae) and palms (Arecaceae), are both economically important and foundational for many terrestrial ecosystems. In this project, we aim to study how leaf morphology in living monocots, specifically vein length per area (VLA), varies among groups and how this trait relates to systematics, with the goal of better identifying fragmentary monocot leaf fossils. We examined VLA in 389 monocot species of 10 orders and 37 families. Monocot VLA ranges from 0.28 to 16.6 mm mm^-2, while the previously reported dicot VLA range is from 0.4 to 24.4 mm mm^-2. We used one-way ANOVA and Tukey’s honest significant difference (HSD) to test for significant differences in mean VLA between orders and families and found both were statistically significant (p<2x10^-16). There were significant differences in mean VLA between orders, with Poales, Arecales, and Zingiberales being the most different compared to other orders (Tukey’s HSD test p<0.01). At the family level, Tukey’s HSD test revealed significant differences in VLA means for Asparagaceae/Orchidaceae (Asparagales); Commelinaceae (Commelinales); Dioscoreaceae (Dioscoreales); Alstroemeriaceae/Liliaceae/Colchiaceae (Lilales); Poaceae (Poales); and Zingiberaceae/Musaceae (Zingiberales) compared to other families (p<0.01). For our largest sampled order, Zingiberales, we compared measurements of leaf length, width, and area with VLA and found family-specific relationships although there was no ordinal level relationship between VLA and leaf shape. We tested the systematic utility of VLA and leaf shape measurements with examples of fossil Zingiberales leaves, some of which are confidently assigned to a family, though others are ambiguous. While further sampling across monocots will be necessary, these results suggest that VLA is distinct enough to use in future studies to aid in the identification of fossil monocots, which is critical for downstream analyses such as determining how monocots responded to past climate changes and examining monocot leaf trait evolution.