none;"> The branching pattern of a tree is its topology.</span> showing the smallest value of the sum of all branches (<i>S</i>) as an estimate of the correct tree.&#160; However, construction of an ME tree is time-consuming because, in principle, the <i>S</i> values for all topologies must be evaluated. Because the number of possible topologies (unrooted trees) rapidly increases with the number of <a href="javascript:TextPopup(this)" id="HotSpot36301" class="glossterm">taxa</a><script type="text/javascript