Is a black eyed pea actually a pea or a bean?

We put this to Claire Domoney, from the John Innes Centre:

Claire - No. Actually, it's a member of the Vigna genus if I remember correctly and certainly not a pea.

[Other members of the genus Vigna include the Azuki Bean, Mung bean and Cowpea. Peas are Pisum sativum.]