Plotting a non-ultrametric tree with dotted lines to aligned tip labels

phytools already has an internal tree plotting function that uses dotted lines to connect the tips of non-ultrametric trees to aligned tip labels. This function can be seen, for instance, in the phytools method plot.cophylo (e.g., here).

However, it is also easy to script essentially the same functionality using plotTree or plotSimmap internally. For example:

library(phytools)
tree

## 
## Phylogenetic tree with 26 tips and 25 internal nodes.
## 
## Tip labels:
##  B, L, Q, D, S, P, ...
## 
## Rooted; includes branch lengths.

par(fg="transparent")
cw<-reorder(tree,"cladewise")
plotTree(cw)
obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
par(fg="black")
text(rep(max(obj$xx[1:Ntip(cw)]),Ntip(cw)),obj$yy[1:Ntip(cw)],
    labels=cw$tip.label,font=3,pos=4)
for(i in 1:Ntip(cw)) lines(c(obj$xx[i],max(obj$xx[1:Ntip(cw)])),
    rep(obj$yy[i],2),lty="dotted")

In this case, the tip alignment (& dotted lines) are based on the highest end-point of any edge in the tree. For ultrametric trees, we can also add a further offset if desired. For instance:

data(anoletree)
plotTree(anoletree,fsize=0.6,ftype="i",ylim=c(-1,Ntip(anoletree)),
    plot=FALSE)

obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
xlim<-obj$x.lim
ylim<-obj$y.lim
offset<-0.1*diff(xlim)
xlim[2]<-xlim[2]+offset
plot.new()
plot.window(xlim=xlim,ylim=ylim)
cw<-reorder(anoletree)
text(rep(max(obj$xx[1:Ntip(cw)])+offset,Ntip(cw)),obj$yy[1:Ntip(cw)],
    labels=gsub("_"," ",cw$tip.label),font=3,pos=4,cex=0.6,offset=0.02)
for(i in 1:Ntip(cw)) lines(c(obj$xx[i],max(obj$xx[1:Ntip(cw)])+offset),
    rep(obj$yy[i],2),lty="dotted")
par(fg="transparent")
plot(cw,lwd=3,add=TRUE,xlim=xlim,ylim=ylim)

## no colors provided. using the following legend:
##        CG        GB        TC        TG        Tr        Tw 
##   "black"     "red"  "green3"    "blue"    "cyan" "magenta"

par(fg="black")
add.simmap.legend(colors=setNames(palette()[1:
    length(mapped.states(anoletree))],mapped.states(anoletree)),
    prompt=FALSE,x=0,y=-1,vertical=FALSE)

[Ed. Note that an earlier version of this post had an obvious error in the above script - resulting in a nonsensical plot. This version should be fixed.]