Galore/Vesuvius is amazingly floriferous and a strong grower. It's color is nearly identical to Etoile Violette, though the blooms are larger (and shaped differently).

Rhapsody is more of an indigo blue, slightly larger flowers, slightly less vigorous though still a winner.

Romantika and BP are very dark, R has larger flowers and is a smaller plant compared to BP. Many report mildew issues on R, though mine does not have that problem. Another dark one with possible viticella blood is Negritjanka.

You've picked 4 winners. In terms of size of flower, Rhapsody, Romantika and Vesuvius/Galore are larger. In terms of number of blooms, maybe V/G or BP.

Another option might be Viola which is a floriferous and a reasonably dark purple. I have had mildew on it one time early in its life in my garden and the mildew was on the flowers, looking like cotton balls. Since that time, it has never had mildew. My experience with both Romantika and Black Prince mirrors Mike's. I have Negritjanka but it was purchased late last season and hasn't bloomed for me so have never really seen it in bloom in person.

IMO, 'Negritjanka' (name translates to 'African Girl') is the darkest flowered clematis I've encountered - a deep, dark smoky purple. It is a cross between 'Gipsy Queen' and a viticella and offers the best of both parents - the larger flowers of GQ and the floriferousness and hardiness of the viticella. It has rapidly become one of my more favored selections.

Sorry, no photo :-( You can check Google images, but I'd not rely on good color quality......most will miss the depth and smokiness of the bloom color.

I love my Romantika. It appears almost black at times. I haven't had problems with mildew on mine either.

I also have Negrijanka, and although it is very dark, I prefer the Romantika which maybe has just a little more red in it's coloration

Negritjanka
{{gwi:574244}}From clematis

Romantika
{{gwi:574245}}From clematis

Thank you, everyone, for your input.

I finally made a decision. It's now obvious that I need TWO clematis (who can buy just one?)-- so after much agonizing, I settled on Rhapsody and Viola.

My roses are gonna love these, aren't they!

Kate

Sort of like Lays potato chips, then again who can stop with two!!! I think you are going to become assimilated like the rest of us Kate! LOL ;)

Worse than potato chips!

Enablers, enablers that's what you are! :) Much worse than potato chips but much better for you. Clematis folks are equally as bad as the rose lovers, and I have fallen deep, deep into the vortex of both, never mind all the cut flowers I grow too! I must, however, say thank you, of all the vices there are out there, being a rosaclemaflowerholic is not such a bad thing! Right? Kat

Couldn't agree more Kat. There are definitely more sinister vices out there that any of us could be smitten by. Love that new term--rosaclemaflowerhalic!!! Too cute! This coming from someone that swore he would not order any clematis this spring and I have 6 on order and 30+ clematis seedlings I am nursing along, not to mention all the other baggies with vermiculite and seeds still waiting for germinations. Of course that does not include all the winter sown containers I have outside and the multitude of other seeds I still have to plant the conventional manner. LOL

No not shameless, but rather a reflection of how we can all be enchanted by plants and the miracle of starting them from seed to see what we get. I keep telling myself this each and every time I wonder what I will do with them all this summer and how much fun it is going to be keeping them watered if the last two summers are predicting what this summer will be like! LOL

Besides clems, roses, I love hardy geraniums and Coral Bells, let's see now, sedums, ground covers, tulips, baby fish, waterlilies, I could go on and on. Clematis just has so many virtues that makes them such a favorite of mine.