Here are a few more plotting options for boxplots:
Let’s start plotting the full set
plot(b$mod, b$x)
Plot labels for a subset in full set plot (label all points x < -1)
text(subset(b$mod, b$x < -1), subset(b$x, b$x < -1), subset(b$site, b$x < -1), cex=0.6, pos=4, col="red")
Plot subset with x > -1
plot(subset(b$mod, b$x > -1), subset(b$x, b$x > -1))
Plot horizontal gridlines
grid(nx = NA, ny = NULL)