marsh yellow cress, Rorippa palustris

Marsh yellow cress is native to wetlands of North America, Eurasia and Africa. It now has spread to South America and Australia. So what is it good for? Not much! The Navajo used it in a ceremonial eyewash. Mustard as eyewash? But it is good for our water, like all those other wetland filters. And it makes great puzzles. PFor instance, pants in the Rocky Mountains present very differently than this one in a fallow field in Michigan. Botanists have spent decades, even centuries, trying to describe and name all the variation. But that variation, as Al-Shehbaz says in FNA, "Is continuous in every character". It defies description! Marsh yellow cress is in every state and province except HI, and on SPM. Lenawee Co MI, 6/16/11. Mustard family, Brassicaceae.