What is this flower?

[Raissermesser]

This is an annual weedy flower that crops up in this part of North America, and it has me stumped. Here's a couple of photos. The first is a clump of these flowers in some briars (wild blackberries). Note that they have three blue petals, and that makes me think trillium, but the leaves are blade-like. You can see buds near the flower in the center. The plant is from 1' - 1.5' high (30 cm - 46 cm).

Here's the second. In the background you can see some oxalis.

Any ideas what this is?

 

[Intrigued]

I think it's some kind of Spiderwort. Try googling "spiderwort" and see what you think.

 

[Billski]

This is ’Sweet Kate’ Spiderwort

‘Better Homes and Garden'

 

[Raissermesser]

Thanks. It comes up here as a volunteer in odd places, and we thought it was a weed.

 

[John Rose]

... this part of North America, ..

Which is . . . where?