http://jnlnet.wordpress.com/2009 ... gree-angle-using-r/

labels <- month.name[1:12]
mp <- barplot(1:12, axes = FALSE, axisnames = FALSE)
text(mp, par("usr")[3], labels = labels, srt = 45, adj = c(1.1,1.1), xpd = TRUE, cex=.9)
axis(2)