 The several groups and subgroups are particularly situated as branches of the tree to indicate ordered lineal relationships between all the organisms shown.Further, any group may (or may not) be considered a taxon by modern systematics, depending upon the selection of its members in relation to their common ancestor(s); see second and third diagrams.The term "monophyly", or "monophyletic", derives from the two Ancient Greek words (), meaning "alone, only, unique", and (), meaning "genus, species", and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a "unique" common ancestor.