Sorrel

 

It may be known as Common Yellow Wood Sorrel to some, but it appeared quite uncommon to me as I ambled along the Norwottuck Rail Trail last week. I thought at first that it must be a kind of shamrock. Then I read this on thespruce.com:

"Wood sorrel is also often confused with shamrocks—another plant in the clover family. Sorrel is sometimes called 'false shamrock,' and during St. Patrick's Day season, it's common to find yellow wood sorrel misbranded and sold as shamrock."