important clade of plants (In APG II and III)
The name commelinids is a plant taxonomy plural, not capitalised. It is used by the APG II system for a clade in the monocots, which in its turn is a clade in the angiosperms.
The commelinids are the only clade that the APG II has named in the monocots. The remaining monocots are a paraphyletic unit, sometimes referred to as the "basal monocots".