Variety reverting to species?

In 2007, I planted two kinds of Lamium maculatum in the same bed: "Aureum" and "Pink Pewter." Both are deliriously happy.

In mid-summer of this year, I discovered that around the edges of one of my Aureum specimens, the plain old species was growing, as shown in the photo.

Is the Aureum reverting to species? If so, what's the mechanism for this phenomenon? These guys don't reseed, do they?

(The Pink Pewter don't seem affected.)

I used to have 4 or 5 varieties that seemed to diminish while what appeared to be an unremarkable type (like yours) started to dominate. Ended up ripping all of them out as the roots were invading other perennials.

I finally found time to take a closer look at the plants, and indeed, the species is a separate plant: it just wormed its way among the species leaves.

I didn't know that Lamiums formed seeds: they're so good at self-cleaning that I never observed seed pods.

Thanks!