MZR of galaxies with 0.15 < z < 0.26: field galaxies (panel a), cluster galaxies at R < R₂₀₀ (green symbols in panel b), PBCG cluster galaxies (red symbols in panels c and d) and ABCG cluster galaxies (blue symbols in panels e and f). For the coeval field galaxies in panel a individual measurements are depicted as cyan symbols, while we show 16th and 84th percentiles, and the medians (50th percentiles) of the distribution of O/H values as black lines which we repeat in every panel for comparison to the cluster galaxies. The percentage numbers in each panel indicate the fraction of 10 ≤ log(M/M_⊙)≤11 objects with high metallicities, above the 84th percentiles (upper black line) of the field galaxies; the symbols for these high O/H cluster galaxies are additionally framed by black squares. The vertical dashed line shows the division between the Mlow and Mhigh sample. The magenta dotted line in panel d indicates a gap in the PBCGs metallicity distribution between high metallicity and low metallicity objects.