Fig. 2

PCA of Poaceae bullilform phytoliths with nine shape parameters. X and Y axis show principal component 1 and principal component 2 that explain 35.2% and 24.4% of the total variance, respectively. Prediction ellipses are such that with probability 0.95, a new observation from the same group will fall inside the ellipse. N = 240. Each data point is labeled with the sample number in Table 1, Additional file 1: Appendix S1