Why do we say “Two peas in a pod”?

Peas from the same pod are nearly identical, lined up side by side. In 1580, John Lyly described two people “as lyke as one pease is to an other.” Back then “pease” was the singular. By the 1600s people heard that “s” as a plural and trimmed it to “pea.” The full pod version shows up in the 1840s.