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Back to July 2018 Newsletter

Maybe Runner Beans are Ambidextrous After All

Bob Wildfong

In last month's ebulletin I wrote about how "Pole Beans are Right-handed, Runner Beans are Left-handed", which discussed the direction that different species of beans will wind around a pole or trellis. I got mail from that one.

Beyond my delight that people actually read our ebulletin, I learned from several readers that pole beans seem to indeed be right-handed, winding counter-clockwise when viewed from above, but runner beans don't seem to follow any particular rule. Some readers explained quite convincingly that their runner beans wound the same way as their pole beans, and even sent photos to prove it.

The difference between runner beans and pole beans is that they are different species of climbing beans. Our typical bush beans, common to nearly every vegetable garden, are called Phaseolus vulgaris. They are the kinds that most people grow for green beans, yellow or white wax-pod beans, or for dried soup or baking beans. Some varieties of that species happen to grow a climbing vine instead of a short bush, so we call them pole beans because they were traditionally grown on tall poles. The pods and edible seeds are essentially the same as the bush beans, and since pole beans and bush beans are the same species, they can cross with each other. (*)

Runner beans, or Phaseolus coccineus are a different, climbing, species that are often grown for their large, colourful flowers - usually red or white. However, the green pods are delicious and tender when you pick them small, and the large seeds can be cooked to make a variety of dishes traditional in many parts of the world.

Why do runner beans twine left-handedly for some gardeners and right-handedly for others? We're not sure. Although the winding direction of vines has been studied for a long time - Charles Darwin pointed it out way back in 1865 - the reason seems very complicated. If you're curious, here's an article that shows just how complicated.

Check your runner bean vines, and let us know how they like to twist!

 

(*) Typical bush beans and pole beans (Phaseolus vulgaris) are compatible to breed with each other, but every flower is tightly curled up preventing insects from reaching the pollen. That means they normally don't cross, even over short distances.

Runner beans (Phaseolus coccineus) have open flowers that allow insects to reach the pollen. That means different runner beans can cross with each other over long distances, but they don't cross with pole or bush beans at all because the species are too different genetically.

--

Bob Wildfong is Seeds of Diversity's executive director

Photo: Member Dirk Groenenberg shows his pole beans on the left and runner beans on the right, both winding the same direction (right handed).

 

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