Sentence:  ...single <WSD>taxonym</WSD> (however it may be artificially segmented into subsidiary taxa) ; but if collateral branches are later found, or reconstructed, or attached by the systematist — branches each one of which includes the ancestor — there is an embarrassment of inompatibles in the taxonomics, for the reason justifying the creation of new taxa at the cladal fork to express the evolutionary divergence is extraneous to the taxonymic unity of any one clade. 
Meaning of the word marked with <WSD> tags:  A word used for classification purposes, that is, one that makes up part of a taxonomy.