Why anthoceros is called synthetic group?

Anthoceros, a genus of hornworts, is often referred to as a "synthetic group" because it represents a collection of taxa that share certain morphological and reproductive traits, but may not necessarily reflect a single evolutionary lineage. This classification is based on observable characteristics rather than strict genetic relationships, highlighting the complexities of plant taxonomy and evolution. As such, the term underscores the challenges in accurately defining groups in the diverse plant kingdom.