Poem

[ann10]

In which poem will you find the name Gwenwynwyn

[HGKinsey]

It can be found in one of the books of the Mabinogion, in a tale entitled Culhwch and Olwen. Although I'm not sure if it is  in the form of a poem.

[RevShirls]

You can find The Mabinogion online here: 

http://www.missgien.net/arthurian/mabinogion/

[RevShirls]

See also this page about the Welsh Triads:

http://camelot.celtic-twilight.com/triads/

xiv Three Who Had The Command Of The Fleets Of The Island Of Britain (Seafarers) of the Island of Britain:
Geraint son of Erbin,
and Gwenwynwyn son of Naf (Naw),
and March son of Meirchiawn.
Each of them had six score vessels with six score men in each.