In message , Mike Lyle
writes
Red kidney bean beans are smaller than runner bean beans, so they must
be a different variety at least. I find it all rather confusing. Even
the garden centre has at least thirty different types / varieties of
"beans" for sale - and from what someone said in another post broad
beans and runner beans aren't even related! The word "bean" seems to be
somewhat generic in usage and confusing for an old has-bean like me. LOL.

I think most (all?) of them are just cultivars of Phaseolus vulgaris:
they come in a wide range of forms. Not the broad bean clan, of course:
they're Vicia faba.

Many beans are varieties of Phaseolus vulgaris. The seeds of this are
toxic if not cooked (sufficiently; apparently slow cookers increase the
toxicity). Runner beans are Phaseolus coccineus, of which Wikipedia says
"Runner beans contain traces of the poisonous lectin,
Phytohaemagglutinin, found in common beans and hence must be thoroughly
cooked before consumption." Butter beans are Phaseolus lunatus. Mung
bean is Vigna radiata. Hyacinth beans, another species which requires
prolonged boiling, is Lablab purpureus.
--
Stewart Robert Hinsley