Ranunculus ficaria and Caltha palustris (Marsh Marigold)...I always get the two mixed up. In fact, I'm still not sure which is which. In any case, I have a whole lot of one of them growing and blooming in my garden right now. I love how in a matter of weeeks in creates a substantial green ground cover, making everything look all "springy" and then...it disappears. Yeah for ephemerals!

Also, I agree, "lesser", hmph.