Rotational period distribution of 0.4−0.6, 0.7−0.9, and 0.9−1.1 M_⊙ stars (respectively shown as tilted triangles, crosses, and tilted squares) in star-forming regions and young open clusters is plotted as a function of stellar mass. The panels are ordered by increasing age, from top to bottom and left to right. The few black tilted crosses in NGC 6530, M 50, and Praesepe are stars rejected from the samples for reasons explained in the text. The rotational periods of stars outside the selected mass bins are shown as small dots, as are subsamples not rich enough (i.e. N_star< 15) to yield statistically meaningful percentiles and therefore rejected from the analysis.