It doesn't seem correct chelle, for a start 'flore pleno' usually means double flowers.
Secondly, Filipendula hexapetala is a synonym of Filipendula vulgaris ..
http://www.theplantlist.org/tp...
Which is on this site .. there is a Flore Pleno of vulgaris, double.
http://pss.uvm.edu/pss123/perf...
Let's see if we can track it down .. Grandiflora has large, white flowers .. but I'm only finding Filipendula vulgaris which looks like yours.
http://www.thewildflowersociet...
http://luirig.altervista.org/f...
http://www.google.co.uk/search...
