Delphiniums are hard not to notice in the landscape. They are members of the buttercup family, and, if you take a good look at the deeply dissected, maple-like leaves, you will see the family resemblance. But it is the impressive height and tightly packed spikes of oddly shaped flowers that gain delphiniums so much attention. The 'Black Knight' cultivar of delphinium sports semi-double, dark purple flowers. Grow 'Black Knight' when a mousy little wallflower of a plant just won't do.