I just posted up a function to create a star phylogeny (that is, a completely unresolved multifurcating tree) on my R phylogenetics page (code here). Very simple, and it seems likely that this can already be done with an existing R function that I am not aware of.
Basically, recalling back to the structure of a "phylo" object in memory, we just need to create an edge matrix containing n+1 (for n species) in the left column and 1:n in the right column:
Then we can optionally assign branch lengths, if they have been provided by the user:
Finally we combine these elements into a list and assign the class "phylo":
and we're done.