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So you think you know what a pea is? A spherical green seed that grows in a group of other peas inside a pod. In order to get at the peas, you need to shell them, by splitting the pod into its two natural halves, which look like little sailboats. Indeed, in ancient Rome, they used the same word, phasellus, for a small sailboat or a kidney bean.* Ancient usage makes it clear that the word referred to the kidney bean and not the pea, which is pisum in Latin, whence the species name for the garden pea, Pisum sativum.

The word phasellus lives on in the species names of many other beans in the slightly altered form Phaseolus, as in P. lunatus, the lima bean.

Peas and beans both belong to the pea family, Leguminosae, because their seeds grow in pods (legumes), and their roots form symbiotic clumps with bacteria that produce nitrogen.

Our vernacular terminology for the seeds of these very useful plants follows a logic of its own. There are, in normal parlance, three kinds of legume seeds: peas, beans, and lentils. Peas are spheres, lentils are small flat disks, but beans? It is not easy to define a bean. Yes, many of them are kidney-shaped but not all. Davidson essentially throws up his hands and defines beans as “any legume whose seeds or pods are eaten, and which is not classed separately as a pea or lentil.” So if the legumes are not in the pea (Pisum) or lentil (Lens) genera, they are beans. All three groups of edible legumes can also be referred to collectively as pulses, the sturdy traditional English term (from Latin puls, a thick soup made from pulses, e.g., the mess of pottage for which Esau sold his birthright—conventionally said to be a lentil soup.)

All pulse seeds are dicotyledons. They develop from double seed leaves (cotyledons) into two halves that split apart easily when dried seeds are hulled. Split peas are the most familiar example of this. In India, dried pulses are called gram when they are whole and dal when they are split.

All that having been said, the only straightforward answer to the question “What is a pea?” is: A pea is a pea is a pea.

*The locus classicus for phasellus as boat is a poem by Catullus (Catullus 4).

†Latin legumen referred indiscriminately to pod and seed. In more precise botanic lingo, “legume” means the pod, or a plant with nitrogen-fixing root clumps whose fruit (the reproductive organ that holds the seeds) is a two-sided pod whose halves look like boats.

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