I'd go with pigeonberry (Rivina humilis), as it meets all of your criteria. However, I'm not positive it will grow thick enough to prevent widow's tears from also growing.

I grow a lot of turk's cap in my shady garden and ferns although they need more water than the tc. My columbine is thriving in early spring and then kind of recedes before the turk's cap gets big.

Good pkponder, I bought a turk's cap yesterday. Right now the area gets afternoon sun and I know turk's cap can take that. My columbine are receding right now too.

I thought of Pigeonberry also. It's beautiful with its red berries and pink flowers at the same time and is one of my favorite plants for dry shady areas. It has a carrot like root that stores water and doesn't wilt even when everything else is wilting.

Horse herb and Frog fruit are other natives that will grow in dry shady places.

All three of these will take sun also.

http://www.wildflower.org/plants/result.php?id_plant=CAVI2

http://www.wildflower.org/plants/result.php?id_plant=PHNO2

Here is a link that might be useful: Pigeonberry ....

Have you considered Bear's britches? I don't know if it is a native. I planted 2 plants, one remains several years later. It is interesting withunusual foliage and a flower spike now. I've read it can be invasive but has not been at all for me, in fact I hope it will multiply...smiles

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I am trying new this year Peter's Purple Monarda behind and Grand Parade (pink) Monarda in front in late morning sun. The Peters' purple is taller (abt 4') and narrower, an the grand parade is shorter and wider. Blooming now and looks very pretty together. They've been blooming about a week so far and look like they may continue awhile. I hear these cultivars don't reseed badly....we'll see lol!

I second Turk's cap for behaving around columbine.

My Turk's cap looks wilted most of the time. No one else has complained about that. Do you just get used to it or is my ground hotter and dryer than anyone elses on this whole planet? LOL

Anyway, you might take a look at Mexican oregano which I suggested on another thread. It never seems to run out of steam no matter how hot and dry all summer long. It just keeps on flowering.