(the default).}
\item{tip.label}{a character vector giving the tip labels; if not
specified, the tips "t1", "t2", ..., are given.}
- \item{br}{either an R function used to generate the branch lengths
- (\code{rtree} or \code{NULL} to give no branch lengths) or the
+ \item{br}{an R function used to generate the branch lengths
+ (\code{rtree}; use \code{NULL} to simulate only a topology), or the
coalescence times (\code{rcoal}). For the latter, a genuine
coalescent tree is simulated by default.}
\item{...}{further argument(s) to be passed to \code{br}.}