I have them in my garden too, also grown from seed. They're called Yellow Flag, and in some states they are listed as pesky weeds.

Here is a link that might be useful: Iris pseudacorus

I thought yellow flag is an invasive water plant?

Iris pseudacorus is a class C noxious wetland (not water) weed here. While often at the edges of a pond, lake, stream, it will grow in areas that remain boggy in winter, are completely dry in summer. I would think it would be pretty happy in a garden with some water, some attention - there's a huge stand of it growing in a low field just outside of town that's remarkably pretty in summer.

No judgment on people growing it in a different climate than my own - it's not the best yellow iris for my area given its reputation here ;-)

I received a patch of this iris from a friend who regularly gives hunks away out of her patch. It is very pretty, spreads only out from it's orginal area (I've never found a stray across the yard) and I appreciate the color contrast with my siberian purple ones. I few years ago my patch just got too big and it was not easy to divide up (think dividing Hosta that's really big) but my husband hacked at it with a shovel and we got clumps to give away. I think I will have a year or two before I have to do that again.

I would move it to a spot away from other flowers, a spot it can call it's own, not right dab in the middle of the bed but off to the side.

From the foliage, it looks like it might be in the Siberian Iris line..doesn't look like a bearded iris. That yellow should look great with purple companions.

It's very pretty.