Simple method to draw boxes around clades on a plotted tree in R

I just wrote a simple function for drawing a box around a clade. This needs a lot of refinement, but it works as follows:

cladebox<-function(tree,node,color=NULL,...){
    if(is.null(color)) color<-make.transparent("yellow",0.2)
    obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
    h<-max(nodeHeights(tree))
    parent<-tree$edge[which(tree$edge[,2]==node),1]
    x0<-max(c(obj$xx[node]+obj$xx[parent])/2,obj$xx[node]-0.05*h)
    x1<-obj$x.lim[2]
    dd<-getDescendants(tree,node)
    y0<-min(range(obj$yy[dd]))-0.5
    y1<-max(range(obj$yy[dd]))+0.5
    polygon(c(x0,x1,x1,x0),c(y0,y0,y1,y1),col=color,
        border=0)
}
library(phytools)
plotTree(tree)
cladebox(tree,42,make.transparent("red",0.2))
cladebox(tree,45)
cladebox(tree,37,make.transparent("green",0.2))

If we want to use non-transparent colors, we can just add the tree backk on top of our boxes. For instance:

plotTree(tree)
cladebox(tree,42,"red")
cladebox(tree,45,"yellow")
cladebox(tree,37,"green")
plotTree(tree,add=TRUE)

(My apologies for the hideous color choices!)