Tony wondered about the species found on willow in his woods (March 2nd blog). Spores from this find are long, I made them to be up to 11.5 - 12µ long which would be consistent with F.elastica.
Spores of F.velutipes are only up to 9.5µ long.
The photos above are of F.velutipes growing on gorse, the first with snow was taken in Jan 2010 and the second one in Jan this year. They look exactly as the fb's in Tony's blog ---- the gills of velutipes are possibly more closely spaced.
The small fb's in the lower two photos were taken on 11th March and were growing on the cut ends of a willow. The spores of these were only 8µ long so clearly fit F.velutipes. Tony has searched the literature on the web and finds there is another Flammulina, F. rossica, with long spores like elastica and also from salix but not mentioned in the Field Mycology 12 (2) p39, 2011 article by Geoffrey Kibby.
These Flammulina species all look alike so finds growing on willow, at least, need to be examined by microscopy to determine which species.