Gentiana linearis

Northeastern North America. A narrow leaved, species of Bottle gentian, (or possibly a hybrid, but the seedlings are all the same).

It blooms in summer. The stems are 30 to 60 cm long, lax in habit, producing sprawling plants with upturned flower heads. For this reason they are ideal in amongst other similar height plants that can form a framework and extend the other plants' season. The flowers are 2 to 4 cm long, a blue color and bottle shaped with fused petals (sympetalous) and closed mouths. Yet still they make copious seed and will pop themselves in all sorts of places. Not ideal for troughs as both too tall and seedy, but its great in a perennial border or in naturalistic planting schemes where new plants are valuable and easily 'edited'. The foliage is hairless with a glossy sheen to it. Easy to grow, border, rock gardens etc. SUn to part sun is best. Hardy and drought tolerant once established.

The flowers are clustered at the top of the plant or in the axis of the top leaves. The clusters of bee pollinated flowers who need to be heavy enough to force the petals open or rip a feeding hole in the side where smaller insects can piggy back. 

Te second photo is a but ratty, the plant is under duress in the shade. 

peupleloup, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons