In my garden I have a perennial (at least in a second year) in two varieties (one white-flowered, one red) of the scrub pictured below. I collected seed from it last year and I got seedlings from it this year (seedlings are not pictured).
The leaves are sharp and wound around the stem. The flowers are coming out of the stem as well. It flowers in July and August.
The red variety (not pictured) is a little bit weaker than the white one - it is smaller and flowers less and later.
The scrub I have consists of several stems which have been cut down last autumn and now they are back like if nothing has happened.
The white variety is about 1.20m high; the red one 0.80-1m.
Thanks for giving me a hint on its ID.
click to enlarge the images