It looks just like 'Clematis' to me too. The spathes look the same
too (not those of a pure I. pallida).
It is clearly not pure I. pallida, but related. I interpret
'Clematis' to be in the old diploid category, with things like 'Queen of May',
'Perfection', 'Rose Unique', 'Quaker Lady', 'Sambucina', 'Flavescens',
etc. It clearly has much I. pallida in it's ancestry, but I think there is
a definite element of I. variegata there too. If this photo is correct, it
would tend to imply that 'Clematis' and 'Lady Phyllis' are synonyms.
The only flattie I know that looks like pure I. pallida (but it is a
plicata) is 'Little Freak'.
Never seen a flattie I. aphylla - that would be fun.