white pinwheel

http://www.google.com/search?um=1&hl=en&rls=com.microsoft%3Anl&biw=1106&bih=666&tbm=isch&sa=1&q=marasmiellus+candidus&btnG=Search&oq=marasmiellus+candidus&aq=f&aqi=g1&aql=1&gs_sm=s&gs_upl=490903l490903l0l530554l1l1l0l0l0l0l37108l37108l9-1l1l0

my first thought without research was epiphyllus (because it is common in dutch), but after a little research on the net i found candidus ( and this one are here and in america confirmed) i tend more to candidus, but both are very similair.

thats not only a mushroom and maybe not genus marasmiellus. it could be marasmius epiphyllus, this one is also as juvenile white transparent and has this white stem

Perhaps Marasmiellus?

Those are absolutely beautiful! (Thanks for another new fav!)