 If "C" is a basal clade within "D" that has the lowest rank of all basal clades within "D", "C" may be described as "the" basal taxon of that rank within "D".The concept of a 'key innovation' implies some degree of correlation between evolutionary innovation and diversification.However, such a correlation does not make a given case predicable, so ancestral characters should not be imputed to the members of a less species-rich basal clade without additional evidence.