There are so many varieties its hard to choose,..viewing the bloom on the plant tag is really only good for seeing the color as one can not appreciate the size of the bloom however 'Freckles' is a small bloom but never really stops blooming throughout the year,..though in my case it blooms better from Autumn.
Small blooms that produce masses of blooms are just as good as a Clematis with not so many blooms but huge flowers,..i also have a Clematis 'Dorothy Walton',..the flowers are almost of side plate size,..it bloomed great near my back door but the bloom period was affected because it developed a Mildew,..it didn't like the location,..now its in the middle of the garden and loves it there

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Clematis 'Dorothy Walton'.