Hieracium x stoloniflorum is one of the forms, which hybrids between Hieracium aurantiacum and Hieracium pilosella can adopt, namely the ones closer at Hieracium pilosella: relatively low growing and with typically only 2 - 3 forked arranged flower heads or one single flower head in the inflorescence.
At genus Hieracium there is the tradition to name (stabilized) hybrids resp. hybrid populations differently, depending on to which of the parents they are approaching. Forms of the same hybrid combination which tend rather to Hieracium aurantiacum have Hieracium x rubrum as hybrid name.