In Welsh Folklore Who Are The Ellyllon?

The Ellyllon are the small, elves who haunt and inhabit groves and valleys. This is the name given to the Welsh elves. According to Wirt Sikes in British Goblins they  are tiny, diaphanous fairies.
They are smaller than the Tylwyth Teg and akin to similar beings in Cornwall and Somerset.
They were mentioned by the poet Dafydd ap Gwilym, in a humorous account of his troubles when he was lost in a mist in 1340.
'Yr ydoedd ym mhob gobant
Ellyllon mingeimion gant.'
There was in every hollow
A hundred wrymouthed elves.
Their food is specified in Welsh folk-lore as fairy butter and fairy victuals, ymenyn Tylwyth Teg and bwyd Ellyllon, the latter being the toadstool, and the former a butter-resembling substance found at great depths in the crevices of limestone rocks..  They are associated with fox-gloves, or in Welsh the menyg ellyllon.