Mystery Bean

A couple years ago, I joined Rancho Gordo's Bean Buddies, a group that grows out some of Rancho Gordo's beans, testing them for production in the home garden. The members compare notes on their growing experience of the year's test varieties. We receive the beans in the mail with only a name and no cultural information, so unless the bean is a well-known, or at least Googleable variety, each new-to-us bean is a mystery waiting for us to suss out its clues.

This year, along with my old standards and one new-to-me variety, I have three Rancho Gordo test varieties growing out in the bean bed. I requested these seeds from the 2013 Bean Buddies listing because of their rarity; all three come from Mexico, and the only information I can find on each at this point is the limited information provided to me with the seed: the name and origin of each variety. The first is Negro Delgado de Arbol, a variety from Cuicatlan, Oaxaca, that in my garden has vigorous vines with flower stalks that set four to six small pods that are tightly packed with small black beans. So far, the bean appears to be very productive. The second is Frijol Cacahuatle Putla, another variety from Oaxaca. This bean has short runners and doesn't set terribly prolifically, though each long pod has a good number of pretty, pink- and purple-mottled beans inside. Frijol Cacahuatle Putla definitely falls into the Phaseolus vulgaris species that many of our edible-podded and -seeded beans fit into, at least in the Western hemisphere. Negro Delgado de Arbol looks very Phaseolus vulgaris-y to me, too; though if it isn't P. vulgaris, the only other option it could be would be Phaseolus acutifolus (Tepary bean), but the bean is shaped like a P. vulgaris, not mini-lima bean shaped, like a Tepary bean.

Though most people have seen them, it is important at this moment to remember what a standard Phaseolus vulgaris vine looks like: twining round stems that are either green or purple; trifoliate perfect teardrop leaves; small white, pink, or purple flowers that occur in pairs along the blooming stems; and a little bit of rough fuzz all over the plant and bean pods (unless it is "greasy" variety). If you can picture that, you can picture a tepary bean vine, that looks quite similar, but has sharper-shaped, smaller leaves and seeds that are flattened like lima beans. Here are a couple photos of P. vulgaris vines to spark your memory.

P. vulgaris blossom, in this case on a Goldmarie vine.

P. vulgaris leaves on Blue Shackamaxon.

The third bean I'm growing out from Rancho Gordo is the most mysterious; its name is Frijol China Putla, but despite its name, it isn't like what we usually call china beans, which are usually P. vulgaris and produce fat, nearly-round dried beans that cook up to creamy deliciousness. Instead, it appears to be a cowpea of some sort, either Vigna unguiculata ssp unguiculata—the same subspecies from in which black-eyed peas and zipper peas and many other similar "field peas" live—or Vigna unguicalata ssp sesquipedalis. V. unguicalata ssp sesquipedalis, which I think is the likely candidate because of its vining nature, is the genetic home to the Asian "yardlong" beans, Red Noodle (a garden favorite at our ranchito), asparagus bean, and the like. Both Vigna unguicalata subspecies originated in Africa.

The Vigna unguicalata species has some very identifiable characteristics: vibrant green, hairless leaves; stems with edges; deep red splotches on the vine's joints; long (very long in the sesquipedalis subspecies), many-seeded pods; and finally, large, beautiful, lavender-butterfly flowers. Unfortunately, those evil seed-devouring sowbugs got most of my seedlings right at germination, but a few rallied, and one plant in particular is going to town. It has the tell-tale signs of a Vigna unguicalata.

Smooth, shiny, brilliant green leaves.

Stems with edges and with the distinct maroon splotch at a joint.

Long, full pods, even when immature. Here, a spider hangs out on a just-set pod.

Gorgeous, pea-shaped flowers.

So, I've narrowed down the genetic home of this plant, but I'm still left with questions.

1. Do I eat the immature pod, like a yardlong bean, or the seeds inside, like a black-eyed pea? Either way, what is a traditional Mexican preparation of this plant?
2. Are the Vigna unguiculata subspecies common in Mexico? I'm no expert on Mexican food, but I don't recall reading recipes that call for either black-eyed peas or yardlong beans. 
3. If the V. unguiculata subspecies are common in Mexico, how did they get there? Did they move south from the Southern US where all sorts of field peas decorate the food history? Did they arrive somehow from Asia with a community, thus the name "China"? If so, how and with whom? Did they migrate north from more Afro-Caribbean countries where field peas are part of the food culture?

This plant has a story to tell. I'm listening hard to it as it grows, and I've put my ear to the Internet to hear more. Somehow or another, I'm going to track down this plant's history.