Roots Phylogenetic Trees
root reroots a phylogenetic tree with respect to the specified
outgroup or at the node specified in
unroot unroots a phylogenetic tree, or returns it unchanged if
it is already unrooted.
is.rooted tests whether a tree is rooted.
root(phy, outgroup, node = NULL, resolve.root = FALSE, interactive = FALSE) unroot(phy) is.rooted(phy)
outgroup can be either character or numeric. In
the first case, it gives the labels of the tips of the new outgroup;
in the second case the numbers of these labels in the vector
phy$tip.label are given.
outgroup is of length one (i.e., a single value), then the
tree is rerooted using the node below this tip as the new root.
outgroup is of length two or more, the most recent common
ancestor (MRCA) of the ingroup is used as the new root. Note
that the tree is unrooted before being rerooted, so that if
outgroup is already the outgroup, then the returned tree is not
the same than the original one (see examples). If
not monophyletic, the operation fails and an error message is issued.
resolve.root = TRUE,
root adds a zero-length branch
below the MRCA of the ingroup.
A tree is considered rooted if either only two branches connect to the
root, or if there is a
root.edge element. In all other cases,
an object of class
single logical value for
data(bird.orders) plot(root(bird.orders, 1)) plot(root(bird.orders, 1:5)) tr <- root(bird.orders, 1) is.rooted(bird.orders) # yes! is.rooted(tr) # no! ### This is because the tree has been unrooted first before rerooting. ### You can delete the outgroup... is.rooted(drop.tip(tr, "Struthioniformes")) ### ... or resolve the basal trichotomy in two ways: is.rooted(multi2di(tr)) is.rooted(root(bird.orders, 1, r = TRUE)) ### To keep the basal trichotomy but forcing the tree as rooted: tr$root.edge <- 0 is.rooted(tr)