Here is a thread which addresses that question. It's not the only one.

Jim

Here is a link that might be useful: Non-crossing Bean Species

Here's another.

Jim

Here is a link that might be useful: Bean Cross-Pollination

Thank you Jim!

I had done a search before posting the question but did not find a lot...as much as I like this forum and all the helpful and knowledgeable members, the search function could be improved IMHO.

I read the former threads and I am glad my intuition was right. So I learned that one is safe staying with different genus. I also gather from some of the responses that if cow peas and yard long beans can cross, then so can limas and common beans, even though no one stated this explicitly. Is that right?

Also, that if by any chance, an inter-genus cross happens, this is very rare and it is cause for rejoicing, not concern, as one has then potentially another variety/species? The one thing I did find strange though is that those in the latter case are fertile. Would it not be like horses and donkeys breeding mules but they are infertile (I mean the mules). I know, legumes are not horses....

Don't feel bad, cabrita. I remembered those threads, one of which was mine, so I knew where they were and found them quickly and easily.

Cross-pollination and isolation distances are topics of great interest to most of us beanophiles. We need a comprehensive listing to reference. I had hoped that would be included in the proposed bean lexicon which has been discussed from time to time. Originally, it was thought that this forum could have a FAQ like some other forums have. Unfortunately, from what I have heard on other forums, GW no longer supports new FAQs. We need to check into that.

Jim

There are always exceptions to rules, but in a nutshell, there are few natural interspecies crosses. P. Lunatus and P. Vulgaris do not cross. It is rare for P.Vulgaris to cross with in specie. Cowpeas and Yardlongs are the same species so they will cross within the species. There are few interspecies hybrids in vegetables, and the few that I am aware of are chemically manipulated to make the hybrid.