I think this is misspelled, it should be 'kellermanii' and
the Smithsonian says some authorities consider it conspecific with B. peltata so there likely is a resemblance. B. kellermannii is described as shrub like, with hairy leaves, flowers reportedly fragrant (this last is from the Thompson Guide) It seems to me it has been reported more sun tolerant than a lot of other begonias. I think it would be fine to take a cutting for insurance and just experiment with the way it grows.

Thanks for the correction. It's a misspelling/typo on my part, not the propagators at Strybing.

Some of the info that I found seemed to indicate that the difference, if any, between B. kellermanii and B. peltata includes serrated leaves in the former.

I just noticed that someone I know posted pictures of B. kellermanii on the "other" forum (whose name we can't mention...). Perhaps I should contact her and find out if she knows anything about this species.

One source (I don't remember which and maybe it was for B. peltata) says that cuttings are difficult and it is best started from seed. I've found many "difficult" things easy to root and many "easy" things difficult, so we'll see. I have never dealt with Begonia seeds, but I will try to save some if it produces any. I found a detailed description (link below, probably well known on this forum) about producing seed and growing from seed. It sounds like a little manual intervention is necessary for self-pollination.

So far to my untrained eye it looks identical to many of the photos of plants labeled kellermanii or peltata. I can't imagine it would be hybrid with anything significantly different from these species. If anyone disagrees please let me know.

Here is a link that might be useful: ABS

I don't know why GW zapped the name of the link above. I had typed: "ABS "Growing Begonias by Seed", written by Brad Thompson"

I think I was incorrect to say the plant might be 'sun' tolerant, it is just that the plants with hairy or vestite leaves protect the plant a little from sun burn and also help it retain moisture. The only difference I found in the Smithsonian is that the outer male tepals of peltata are vestite and those of kellermanii are not. I think you can also check the Astrobranch site and ABS site for pictures of these species. If you are successful in selfing this plant for seeds, don't forget a hybrid may look different from its parent. Thanks for sharing those interesting pictures.