Finding Descendants on a Phylogeny

Lets say we wanted to know the inverse of the Most Recent Common Ancestor (MRCA). For example, we highlight the MRCA down below in red and we want to discover all of its living descendants.

To do so, we must travel from the node towards the tips of the tree. At each internal node, we make sure we continue towards the tips. Once we have exhausted all possible branches and tips we could run into, we have our answer! On the below phylogeny those pathways from internal node to the tips is highlighted in blue. Each of the descendants from the node is then highlighted in blue.

Of course we can also see that the most recent common ancestor for the Bushmaster, Fer-de-lance, Eyelash Viper, Rattlesnakes, Cottonmouth and Copperhead is highlighted in red!