Ancestral leek, Allium ampeloprasum, is a common and highly variable wild species native to Southern Europe, according to Roger Phillips and Martyn Rix, in their book, Vegetables (Random House). Variants were found in Western Europe, too -- in Ireland and England, often associated with early Christian sites.
They write that numerous varieties of leeks are now grown, differing mainly in the color of their leaves, hardiness, and tendency to form bulbils at their base.
I've been growing (and sharing) perennial leeks for some years now, obtained through Southern Exposure Seed Exchange. I've been writing about them for a number of years, too.
They're really wonderful and productive. Eaten as young leeks, they're delicious from bottom to top; as a bit older leek, they're still great for the tender parts, with tops for soup.
And productive -- well, each leek that I have now (which I didn't separate in fall) is a huge clump of young leeks, surrounding the original one. The ones I did separate and replant look like these (from last year's harvest).
I'm planning to share a number of clumps in my garden club sale this Sunday; they're winners and productive in my garden.