This grower is fairly sure of this plant identification.
I'm not exactly sure which euphorbia this is but it looks like the wood spurge to me.
Euphorbia amygdaloides (Wood spurge). This is an upright perennial which will grow to 1m high and has dark green, spoon-shaped leaves 8cm long, The flowerheads are yellowish green bracts in mid-spring to early summer.
Watch out it is poisonous and allergenic.
Borders, under shrubs,
Italics = data drawn from parent genus or speciesView Full Plant Finder Record