What is the most obvious, defining physical characteristic used today to differentiate between the Cardigan Welsh Corgi and the Pembroke Welsh Corgi?

The tail appearance

The tail is explicitly identified as the most obvious and defining physical difference separating the Cardigan Welsh Corgi from the Pembroke Welsh Corgi in contemporary breed standards. While the breeds share a common origin and function, centuries of separate development and standardization efforts led to formalized physical markers distinguishing them. The Cardigan possesses a long, full, fox-like tail, contrasting sharply with the Pembroke, whose tail is historically known to be either docked or naturally bobbed. This specific appendage became the hallmark feature used by early kennel societies when formalizing the separation of these two distinct genetic lines.