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//]]></script><span class="glosstext" id="POPUP27639" style="display: none;"> A taxon is the individual unit whose evolutionary relationship is being investigated.  Depending on the study, “taxa” may refer to species, populations, individuals, or sequences within an individual.</span> in the tree, which is referred to as <a href="javascript:TextPopup(this)" id="HotSpot19989" class="glossterm">mid-point rooting</a><script type="text/javascript">//<![CDA