Their flowers, which are perfect (bisexual), often butterfly shaped and quite pretty, are self-pollinating and do not usually cross within species or between species. However in NZ,  the runner bean (Phaseolus coccineous) varieties cross freely. The larger flowers of this species are preferred by bees.

A lot of people get confused with the “climbing beans” and runner beans.  Scarlet Runner Beans are P. coccineus varieties, and these cross very readily with each other  i.e. other varieties of the runner bean (P. coccineus).  Phaselous vulgaris beans may also be climbing beans (or bush beans) but rarely cross with other members of that species as they are self-pollinating.

Peas (Pisum sativum) are self-fertile and do not cross.

Broad beans (Vicia faba) are pollinated by bees and insects and do cross.