The genus of Amsonia is a slow-growing summer flowering perennial, which forms clumps of flowers. Although not native to the UK (they mostly come from North America), it is hardy, though it does prefer sunshine and well drained soils.
The most common form you'll come across is Amsonia orientalis (pictured), which actually is of Turkish origin, and is a great "filler" plant for your borders rising to a height of around 45 cms.
Another popular Amsonia is the larger mouthfull of Amsonia tabernaemontana (pictured) with it's pale blue summer flowers atop willowy stems. If you're looking for more feathery foliage with extraordinary autumn colours, then try Amsonia hubrichtii ("tii" at the end) (pictured), which is generally taller and bigger in size.