  The hierarchical model of galaxy evolution suggests that the impact of
mergers is substantial on the intricate processes that drive stellar assembly
within a galaxy. However, accurately measuring the contribution of accretion to
a galaxy's total stellar mass and its balance with in-situ star formation poses
a persistent challenge, as it is neither directly observable nor easily
inferred from observational properties. Here, we present theory-motivated
predictions for the fraction of stellar mass originating from mergers in a
statistically significant sample of nearby galaxies, using data from MaNGA.
Employing a robust machine learning model trained on mock MaNGA analogs
(MaNGIA) in turn obtained from a cosmological simulation (TNG50), we unveil
that in-situ stellar mass dominates almost across the entire stellar mass
spectrum (1e9Msun < M* < 1e12Msun). Only in more massive galaxies (M* >
1e11Msun) does accreted mass become a substantial contributor, reaching up to
35-40% of the total stellar mass. Notably, the ex-situ stellar mass in the
nearby universe exhibits significant dependence on galaxy characteristics, with
higher accreted fractions favored by elliptical, quenched galaxies and slow
rotators, as well as galaxies at the center of more massive dark matter halos.
