When I first saw this plant, in 1998, it was relatively uncommon. I had trouble finding a name for it; it wasn't listed in my field guides.

Now it is among the worst of the invasive plants in Delaware.

This plant covers acres along streams in Delaware, including the Brandywine Creek floodplain. Note the Virginia bluebells in the foreground. It's ideal habitat for both plants, but the bluebells can't compete.

The leaves emerge in late winter and form a dense mat.

The plant resembles the rare native marsh marigold, but three sepals confirm that it's celandine.

A single plant.

The plant spreads by growing new plants from tubers...

...and from bulblets that grow in the leaf axils.

The leaves die in late spring, leaving the bulblets free to be washed downstream or spread in mud on shoes and bike tires.