Planetary radii are derived for 218 exoplanets orbiting 161 M dwarf stars. Stellar radii are based on an analysis of APOGEE high-resolution near-IR spectra for a subsample of the M dwarfs; these results are used to define a stellar radius-M_Ks_ calibration that is applied to the sample of M-dwarf planet hosts. The planetary radius distribution displays a gap over Rp~1.6-2.0R_{Earth}, bordered by two peaks at Rp~1.2-1.6R{Earth} (super-Earths) and 2.0-2.4R{Earth} (sub-Neptunes). The radius gap is nearly constant with exoplanetary orbital period (a power-law slope of m=+0.01-0.04_^+0.03^), which is different (2{sigma}-3{sigma}) from m~-0.10 found previously for FGK dwarfs. This flat slope agrees with pebble accretion models, which include photoevaporation and inward orbital migration. The radius gap as a function of insolation is approximately constant over the range of Sp~20-250S_{Earth}. The Rp-Porb plane exhibits a sub-Neptune desert for Porb120S{Earth}, being significantly smaller than Sp>650S{Earth} found in the FGK planet-hosts, indicating that the appearance of the sub-Neptune desert is a function of host- star mass. Published masses for 51 exoplanets are combined with our radii to determine densities, which exhibit a gap at {rho}_p~0.9{rho}{Earth}, separating rocky exoplanets from sub-Neptunes. The density distribution within the sub-Neptune family itself reveals two peaks, at {rho}p~0.4{rho}{Earth} and ~0.7{rho}{Earth}. Comparisons to planetary models find that the low-density group are gas-rich sub-Neptunes, while the group at ~0.7{rho}{Earth} likely consists of volatile-rich water worlds.

Cone search capability for table J/ApJ/993/233/table1 (Stellar and Planetary Data)