B. ‘Black Knight’ has possibly the darkest flowers but one should not dismiss B. ‘African Queen’ distinguished by its deep maroon purple flowers with a yellow throat. At Longstock it is more compact than B.‘Black Knight’, a medium grower and perfect for adding some contrast to a mixed border of Buddleja. Also worth considering is B. davidii ‘Purple Friend’.
B. ‘African Queen’ was selected by a Dutch nurseryman W. Schoemaker in 1959.