ETG evolution in stellar mass, effective radius, and effective velocity dispersion, due to major and minor mergers, and envelope accretion. Same as Fig. 1, but with the addition of the potential contribution from z = 3 to z = 0 of envelope accretion (green arrows), that is diffuse accretion of loosely bound stellar systems such that R_e varies with stellar mass as R_e ∝ M_⋆², while σ_e remains constant (see text). While the stellar mass growth attributed to major and minor mergers (black arrows) is based on observational estimates (Sect. 2.3), the stellar mass growth attributed to envelope accretion (green arrows) is chosen ad hoc so that in the upper panel the head of the green arrow lies on the observed z = 0 R_e-M_⋆ correlation.