Book  (Oct 2001)  Page(s) 129-130.  Includes photo(s).
 
Clematis 'Blaaval' Evergreen Group
Trade name" Avalanche
Robin White (England) 1999
C. paniculata x C. marmoraria
... single, flat, waxy, greenish white flowers... six, sometimes as few as four or as many as seven, smooth, papery, overlapping tepals... greenish filaments with creamy yellow anthers... Not for excessively cold and frosty gardens...

Book  (11 Oct 2000)  Page(s) 82.