Fig. 4

Two-dimensional principal component analysis (PCA) of relative abundances (ion counts) of ion masses (m/z) detected using UPLC-FTMS. Only masses corresponding to those expected for alkaloids, extracted from positive mode data, are included. Results are presented as scores (a) and loadings (b) plots. The percent variance accounted for by each principal component (PC) is indicated. For the scores plot, each dot represents a one of four replicates analyzed per plant species. Areas enclosed by 95 % confidence ellipses, containing dots of the same color, define statistically significant class separations [34]. Species abbreviations are defined in Table 1. Loadings representing individual masses are shown as black dots (b). Masses and putative identities, where applicable, are shown for select loadings. A complete listing of loadings data is found in Additional file 16