Discussion on the identification of the invasive sulphur cinquefoil (Potentilla recta) from the native Potentilla gracilis from the CPOP Listserv. Includes photos for reference.
Summary
In June of 2014, several CPOP Listserv contributors discussed various tips and tricks to identify and treat sulfur cinquefoil (Potentilla recta), an invasive forb that looks similar to the native slender cinquefoil (Potentilla gracilis). Contributors agreed that one of the biggest identifying differences between the two plants was the underside of the leaves: where P. recta is green on the underside, almost the same color of green as the top of the leaves, P. gracilis has a white or white-silver underside. It was noted however, that in other regions this characteristic may not be reliable for identification, and other characteristics may need to be used to differentiate between the two species.
Further identification information can be found in Flora of the Pacific Northwest by Hitchcock and Cronquist. See additional comparison photos at the end of this document. Other photos and additional identification information can be found at the University of Washington Burke Museum website as well (http://biology.burke.washington.edu/herbarium/imagecollection.php).