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Plant identification: Blue flowered perennial

I visited a friend's house in April/May and toured her garden. I fell in love with Brunnera, which was in full flower at the time, and she gave me a cutting, which has taken. Next to it was another clump-forming plant with very large and plain dark green leaves, pointed oval and about 15 to 20 cm long. It had a mass of blue bottlebrush-style flowers on thin stalks. I also took a cutting of this, which has really taken off, and I am keen to plant it in my garden, but before I decide where to put it, I'd like to find out whether it prefers sun or shade. It's a perennial and I don't imagine it is rare or unusual, but I haven't seen it elsewhere and would like to know what it is. My friend doesn't know as the plant was there when she bought her house. Thanks for any help.
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I can only presume it is intended to be sarcastic. Interesting sales pitch, for sure. It definitely is the same plant, except that it says here that it flowers in July - October, and it was April/May when I saw it in full flower.
There are may forms of persicaria - some with interesting variegated leaves that do better in some shade, some with deep red, finer and more pointy flower spikes and one which is a good ground cover for front of border or awkward spots. It is much shorter and has flowers that fade from pink to deep red and then coppery brown as they age and the foliage often persists and turns red in winter. There is also a weed form known as red shanks which is to be avoided at all costs.
https://www.rhs.org.uk/Plants/Search-Results?query=Persicaria
Persicaria bistort superba.