我试过了大家说过的expression, 可是还是不对，可能是我某个地方弄错了，比如说paste函数，我不太了解。
有五条线，这里我就不贴代码了，简单画个图，麻烦大家帮我把图例好好看看，谢谢了！！

x1<-paste("nw-ng",expression(r^2),"=0.44","p=0.073")
x2<-paste("w-ng",expression(r^2),"=0.63","p=0.018")
x3<-paste("nw-g",expression(r^2),"=0.37","p=0.082")
x4<-paste("w-g",expression(r^2),"=0.79","p<0.001")
x5<-paste("all",expression(r^2),"=0.48","p<0.001")

plot(c(1,2))
legend("topleft", legend=c(x1,x2,x3,x4,x5), lty=c(2,2,2,2,1),pch=1,col=c(1,2,3,4,1),bty="n")