Feedipedia revised their pea entry to include this: "Pea taxonomy is complex and debatable. In particular, there is no authoritative and definitive way to classify
arvense (field) and
hortense (garden) peas. They used to be considered as separate species (
Pisum arvense,
Pisum hortense) but they are now seen as separate varieties or subspecies of
Pisum sativum (
Pisum sativum var.
arvense,
Pisum sativum var.
hortense,
Pisum sativum subsp.
hortense) or as separate varieties of the subspecies
Pisum sativum subsp.
sativum (
Pisum sativum subsp.
sativum var.
arvense,
Pisum sativum subsp.
sativum var.
sativum) (
Martin-Sanz et al., 2011;
USDA, 2011)."
But they vary a lot in nutritional content. Generally legumes are high in protein (but low in methionine; meanwhile most grains are rich in methionine, so when they're eaten in the same meal with legumes a complete protein is formed, akin to the quality proteins in meat, dairy and fish). The red/yellow/purple/black coloured ones are usually more nutritious than the green ones; and those varieties grown to dry usually have more phytonutrients than those sold fresh. There are other differences; e.g. lima beans, pigeon peas and kidney beans stimulate more gas production than other varieties (not that I've ever seen or heard a chicken fart!) - rinsing away the soaking liquor helps with that.