If your professor desires you to make a
phylogenetic tree of orchids and she provides you tissue from seven orchid
species and one lily, then the most likely reason why she gave you the lily is for
it to serve as an outgroup.
To add, in cladistics or phylogenetics<span>, an outgroup is a group of organisms that serve as a reference group
when determining the </span>evolutionary<span> relationship among three or more monophyletic groups of
organisms. The set of organisms under study that precisely allows the phylogeny
to be rooted is called the outgroup and it is used a comparison point for the
ingroup.</span>
