The brothers Grimm tell a tale explaining an anatomical feature of a bean seed. In The Straw, the Coal and the Bean, a bean seed which is destined for the pot escapes its fate, along with a piece of straw and a lump of coal. The three companions run away but when mishap befalls the coal and the straw, the bean laughs so hard that it splits its sides. A tailor happened upon the bean and took pity, kindly sewing up the legume “but because the tailor had used black thread, all beans since then had a black seam“.
A cute story, but not as true as I’d like it to be! I’m guessing the bean in question was a broad bean (Vicia faba) since it has a long hilum (the bit where the seed attaches to the inside of the pod) which does indeed look like a seam, and is often black. But it can also be white depending on the variety. Research by the Heritage Seed Library indicates that if a variety has seeds with different coloured hilums, this is a tell-tale sign that there has been cross pollination, or that the variety isn’t stable within itself.
The seeds of French and runner beans look different to those of broad bean, but are similar to each other. There can be confusion between the two, as the plants look alike. Both are in the genus Phaseolus, but are different species: the French is P. vulgaris, whilst the runner is P. coccineus. The seeds of runner beans are usually (but not always) bigger than those of french beans. As the Latin name coccineus indicates, runner beans usually have scarlet flowers (though they are sometimes white or a combination of both). But a runner bean is not always P. coccineus, as French beans were sometimes called ‘runners’ in old catalogues!
The way to be certain is to observe the way they germinate. If the foliage which first emerges above ground are the ‘true leaves’ (i.e. typical of that plant), then it is the runner bean, P. coccineus. The seed itself stays in the soil, and its cotyledons (seed leaves) stay enclosed within. This is called hypogeal germination. However, if the seed is hoisted into the air and the seed leaves burst forth, then it is a French bean. The first leaves you see are the cotyledons, followed by the typical leaves. This type of germination is called epigeal. The way I remember the difference is that a runner bean ‘hits the ground running’ so to speak, already producing its true leaves when it unfurls from the ground. The French bean is behind in the process.
Runner Bean: hypogeal germination
French Bean: epigeal germination
Things may just have got a bit more complicated! In the latest Organic Gardening Catalogue, I noticed a cross between a French and runner bean. As it’s listed in the runner bean category, I’m guessing (perhaps incorrectly) the germination style is hypogeal..
This year, I am trialling a non-climbing French bean on my shady fire escape. After success with dwarf tomatoes, I’ve decided to try a short version of this sun loving bean. Interestingly, when I tried runner bean ‘Hestia’ I didn’t have much success, despite P. coccineus coping with more shading.
Biddle, Anthony J., Peas and Beans (CABI, 2017)
Stickland, Sue, Back Garden Seed Saving: Keeping our Vegetable Heritage Alive (eco-logic books, 2001)