Hmm, sounds like genetic confusion! Both Black Knight and the white flowered forms of B. davidii have been produced by plant breeders, they do not occur naturally, and sometimes the genetic information gets a bit mixed up. I'm interested as to whether the white flowers are present on their own stems, or whether both white and purple flowers are being produced on the same stems.

Sounds as though you've got the makings of a mythical tale, with Black and White Knights competing for space. Or is it just chess? Phil J

Just a mention, buddleia is supposed to be cut back to one foot every spring or that's what I read.

Olelady/Barbara