Filipendula hexapetala It is said that F. hexapetala is a synonym for F. vulgaris, however the F. vulgaris that I have grown reached only to about 14 inches, whereas F. hexapetala flowers reliably at least two feet high and is more attractive.
Filipendula rubra - I do not collect seed from this beauty because it must be sown when harvested, and it is finer than dust. In fact, it looks more like dust rather than seed. If there is seed there, I have not found it.