Identification: Fungi ID in Hampshire woodland Armillaria ??

These were growing on a poplar tree in my local woods this morning, they glowed in the sunshine. I took a photo of the underneath, it is a little blurred but hope it helps with ID.. Very pretty whatever it is.

 

For ID, often a shot of one entire single mushroom is needed, with intact base, shot of full stipe, gills and top of cap. So far, looks like either a Flammulina or an Armillaria. Was it on poplar tree roots, lower trunk, higher trunk or branches? Is the tree living, dead, very rotten?

 

@Frog Understand J. It was about 3 foot off the ground on the trunk, not on roots and the poplar was very much alive, but with some cracking on the main trunk. My first thoughts were Armillaria but I have never seen this so bright. I know it was sunny but they were so incredibly orange.