K–S diagram relating star formation rates to molecular gas surface densities. The upper limits to the average molecular mass surface densities in the IRAM beams for six star-forming regions observed in the Leo ring are shown with magenta square symbols. The standard cloud model for the expected FWHM of the lines has been used. The continuum and dotted lines show the K–S relation and its dispersion, as fitted by Leroy et al. (2013) to the inner disk data of galaxies. The shaded areas indicate the molecular gas surface densities typical of the inner regions of galaxies and of outer disks (see Watson et al. 2016).