The "Common" Hypostomus is not a singular fish but rather a broad identification. There are a number of similarly looking Hypostomus that can be nearly impossible to identify even with a catch location thus they are broadly grouped as "Commons". Hypostomus plecostomus was thought to be the "Common" plec imported in the past (thus the reason loricariidaes as called plecostomus/plecos) though there is even some dispute that these were truely H. plecostomus and not some other Hypostomus.