Surrey,
United Kingdom 
On a whim i bought a gomphostigma virgatum but now wonder if it will grow in my ordinary clay based garden that does have some areas that don't dry out but will be in North facing shade much of the day
5 May, 2018
Answers
The RHS has them both listed as being in the family
Scrophulariaceae, so is that a new re-classification [again]
Answered the first post as I start with the least recent and work forward :o) seemingly we are singing from the same hymn sheet Buddle.
5 May, 2018
I've been growing it in ordinary clay improved with grit for several years. The position is in full sun but a bit dry for it which helps limit the size. It is also cut back hard every spring.
5 May, 2018
Ok thanks for that
6 May, 2018
Gomphostigma is a close relative of Buddleja, and one of only three genera in the family Buddlejaceæ.
Although listed as a marginal, I have found it to be happiest in moist rather than wet soil, and it seems to grow fine in clay soil with a high humus content.
It is a full sun plant and will not tolerate a lot of shade. I do not think it will thrive with a north-facing aspect.
5 May, 2018