label lost for this blue-flowering beauty. Anyone knows what it is ?

[François Lambert]

I used to grow this plant in a pot, but these died last winter
But seedlings popped up between the cobblestones where the pot was last year 
Under good growing conditions it reaches a height of 50 cm.
Flowers from early summer till now (end of September), each flower lasts just one day.
This plant grows from some kind of claw shaped rhizome.
Black seeds of 1.5 - 2 mm size.

Your expertise to name this one will be highly appreciated

I'm currently harvesting seeds from these plants and planning to send the surplus (won't be that much) to the seed exchange 

[fermi de Sousa]

Commelina coelestris?
It's a Tradescantia relative,
cheers
fermi

[Maggi Young]

One that I've lost as well, François -  Commelina...... dianthifolia...... leaves too broad  for that species.

[Maggi Young]

Commelina coelestris?
It's a Tradescantia relative,
cheers
fermi

  Oh, maybe - but then it would be Commelina coelestis 

[François Lambert]

thanks a lot - commelina did it.  Just did some search on the Internet and found also a very big resemblance with Commelina tuberosa.  Will search a bit further on the genus to really make sure what it is.  Search finished, yes, it is Commelina coelestis !
Frost hardy to -10°C, which explains why they died last winter (I forgot to bring the pot in to my frostfree winter storage).  they might survive in the open here with some mulch.

[meanie]

I have a few spare seeds for C.coelestis "Alba" and C.tuberosa if anyone is interested.