The Arthurian connection of Ricca (or Ritta) may have originated from the HRB. Iolo Morganwg mentions a story of Rhita Gawr and he gave the source as a o Lyfr Iaco ap Dewi. Rhita settled a dispute between kings Nynnio and Peibio by conquering them and cutting off their beards. He did the same with all the other 28 kings that challenged him and made a mantle from the beards.
That this may not have been an invention of Iolo is the fact that Ricca may well have been of one generation earlier than Arthur since JC 9 and JC 10 indicate that to be the case for the brothers Nynnio and Peibio. This generational placement is in line with Culhwch ac Olwen which indicates that Eigr was married to a Ricca, chief elder of Cornwall.
Nynnio and Peibio ruled in S. Wales and the Liber Landavensis locates a Tref Rita there.