Phaseolus vulgaris is what is called the common bean. The group includes both pole and bush forms. In usuage terms it includes both snap beans ( green or wax) and dry shell beans.
Phaseolus lunatus is the lima bean group both pole and bush.
Phaseolus coccineus is the runner bean group.
Vicia faba - Broad/English bean group.
Vigna sesquipedalis - Long/Yardlong/Asparagus beans
Vigna angularis - Adzuki bean
Vigna unguiculata - Cowpea/Southern pea. As a southerner I don't acknowledge these as beans, but many folks do.
Lablab purpureus - Hyacinth bean
Canavalia gladiata - Sword bean
Glycine max - Soybean group.
Canavalia ensiformis - Jack bean

Good questions. P. vulgaris or common beans include most "string beans" or "snap beans" and they can be bush or pole.

There are a number of named pinto bean varieties.

Runner beans are P. coccineus. They do not cross with P vulgaris varieties and their seed leaves stay in the ground when they germinate.

Lima beans are P. lunatus, also a separate species.

Very good clear classification, farmerdilla.

"Vigna unguiculata - Cowpea/Southern pea. As a southerner I don't acknowledge these as beans, but many folks do. " LOL! I like the way you finessed that one. You expressed that pea/bean dilemma perfectly. I need to remember that when I talk about Eastham turnips, which are actually rutabagas but which no Cape Codder would "acknowledge" as such.

Jim

Don't forget the mighty peanut, or groundnut (Arachis hypogaea)

Thank you. I don't understand why beans are classified into different genera (vicia, vigna, glycine, etc.) but I'm sure there's a reason. I grew scarlet runner beans once, and they didn't seem different to me than other string beans I've grown. Can you tell by looking at them that they're different?

I read elsewhere on this forum that it is possible, but unlikely, for common beans to cross pollinate with each other. Does that mean I can grow two varieties of common pole beans on the same trellis, even if they have about the same maturation rate? Or should I stagger them in time? And if that's necessary, how many days' time is necessary?

Thanks again.

Pole common beans can cross. It appears to be rare among bush beans. If you are just growing ordinary common beans like Fortex where you can always buy more quality seed of the same variety, it may not matter. If they do cross you may even find yourself with an interesting variety.

If you have a valuable rare variety that you want to preserve, or if you are going to offer seed to others who will expect it to be a pure line, then separation by distance is necessary. As pole beans continue to bloom over a long period, separation by time is not likely to help.

Grow your valuable variety as far from other common beans as possible and even grow something different such as runner beans in between.

Runners, by the way, tend to cross much more than common beans so seed savers may grow only one variety per year. - Dick

"I don't understand why beans are classified into different genera (vicia, vigna, glycine, etc.) but I'm sure there's a reason."

The fundamental reason is in their genetic differences. In the past, differences in outward physical characteristics were relied on to classify them. Then chromosomes counts were used and now DNA mapping is available.

Two things affect their propensity for crossing or their lack thereof. One is genetics. The other is structure.

Interspecific or even intergeneric crosses are possible with some plants. How likely it is depends on how closely they are related. It isn't a major consideration with beans.

Crossing between different varieties of the same species is what concerns us most with beans. The probability of that happening depends on both genetics and structure, if I understand it correctly. Beans are said to be inbreeding rather than outcrossing, which means that they are self fertile (a genetic trait) and their flower structure inhibits pollinators from depositing "foreign" pollen. Tomatoes are another inbreeding crop. Squash is an example of an outcrossing crop.

For reasons I can't explain, the ability of beans to be cross-pollinated varies according to species. Different varieties of common beans are relatively unlikely to cross. Varieties of lima bean are more likely to cross. I don't know about others.

I hope I've stated this correctly. Please let me know if I haven't.

Jim

Those are good points. Please bear with me for being a little thick, I've still got a couple of questions.

If I grow two kinds of beans that do cross pollinate, will this year's beans be affected? Or will the resulting cross only surface if I save this year's seed and plant it next year?

If I grow a pole lima along with a pole string bean, they might cross?

Thanks again.

You ask good questions, egganddart.

Think of it this way. All parts of this year's plant, including the seeds, are from the same parentage (except for the embryo, if I am not mistaken, and that is a tiny part of the seed). Neither the roots, stems or leaves nor seeds will be changed by crossing with a different variety. There will be no obvious evidence of the male parent's contribution to those seeds until they are grown out next season. And, of course, if the flowers were self-pollinated as they usually are, there will be no difference even then.

Pole vs. bush is a varietal feature. It is passed along genetically like any other trait such as color, shape, etc. Pole limas will interact with bush limas the same way they interact with other pole limas.

Jim

Concur with Jim, but need to reiterate Common bean/ stringbeans do NOT cross with limas.

I didn't catch that limas don't cross pollinate with common beans. Thanks. I want to try pole limas this year.

Funny, I majored in human biology but I'm completely ignorant about the ways of plants.

This much, however, I can guess from greek word roots: hypogaea, in Arachis hypogaea (peanut), must mean "under the earth", or underground -- where peanuts grow.

Thanks again.

Thanks for the assist, farmerdilla. I completely misread the line in egganddart's post where he asked that question. That's why I failed to give a direct answer.

Jim