How to display star for significance in base R boxplot?

To display the star for significance in a base R boxplot, we can use text function. The text function will be helpful in defining the star sign (that is asterisk or *). If the significance is high then three stars are used and the significance is low then a single star is used. We need to use the appropriate position using x and y values.

Example

text(x=1,y=max(df$y[df$x==1]),"***",pos=3,cex=1.5)

Output