I am growing Rehmannia have thought that it was Gesneriaceae but have recently seen it assigned to Scrophulariaceae. Botanica is ambiguous and it is not mentioned in the list posted in the firstQ 2006 Gesneriads.
If I understand correctly, Rehmannia is one of those odd-ball plants that gets moved around and doesn't quite fit. It seems to me I read somewhere that it is being considered for inclusion in Gesneriaceae at this time, and since I have long been somewhat interested in them I was more encouraged to try them. Of course, since there are, I would guess conservatively, about ten thousand plants I'm interested in, I may not get around to growing them in the near future--and anyway, I'm not too sure how well they would adjust to my peculiar climate. Have to do some more research.
My understanding is that rehmannia is no longer considered to be a gesneriad, but once was. I call it, an honorary gesneriad. It just doesn't grow or have the "feel" of a gesneriad. It is like a true perennial type plant. I have a couple growing in the garden and in pots outside.
PS, Nancy, only 10,000 plants you are interested in? How do you keep your list so short? My list would be longer if I didn't already have far far far too many. Sigh...
Jon, my list is growing shorter as my years are getting longer. I'm trying to get my son as interested in gesneriads as I am--succeeded in getting him hooked on gardening early, but he's more interested in trees and shrubs.
Rehmannia has bounced between Scrophulariacea and Gesneriaceae several times over the years, depending on whose classification you look at. Scrophulariaceae has been dramatically redefined in recent years and is now a much smaller family; many former Scrophs are now in Plantaginaceae (!) but Rehmannia is still unsettled and may end up in Phrymaceae (along with Mimulus!) or another family. However, it's definitely not a gesneriad.