Book  (Oct 2001)  Page(s) 119-120.  Includes photo(s).
 
Clematis 'Asao'
Kazushige Ozawa (Japan)
Introduced to England in the early 1980s by Raymond Evison of Guernsey Clematis Nursery
... single, large, deep pink flowers... six to eight tepals which are much longer than broad... almost white towards the centre of each tepal with prominent pink veining. Anthers are yellow.