Book  (Oct 2001)  Page(s) 134.  Includes photo(s).
 
Clematis 'Bonstedtii'
Herbaceous/Heracleifolia Group
(C. x bonstedtii)
Parentage believed to be C. heracleifolia x C. stans
Origin unknown
... single, small, tubular, hyacinth-like, pale bluish white flowers... four tepals... white filaments and yellow anthers...