Sulfur cinquefoil is a noxious weed that invades pastures, rangelands, and open woodlands, where it reduces forage production and wildlife habitat. Aggressive herbicide control of new infestations is good management to prevent them from becoming big and expensive problems. But it is easy to mistake sulfur cinquefoil for a number of our native and beneficial cinquefoils – the flower color and leaf shapes can be very similar. Since it is not good management to use limited time and money spraying beneficial plants, here are some clues to help you make the correct identification.
A few visual characteristics help distinguish the good cinquefoils from the bad. The most consistent and obvious difference is the plant hairs. Sulfur cinquefoil plants have sparse, long (up to 1/4 inch, 6mm), coarse hairs. Botanists call this “hirsute-hispid.” The hairs are on the leaf petioles, stems, flower stalks and bracts. Once you train yourself to recognize these hairs, identification becomes much easier. The hairs on the natives are variable; some have white wooly hairs on the undersides of the leaf, some are fuzzy with short hairs, and some are hairless, but non are “hirsuite-hispid.”
Flower color is a less dependable identifier because of the variability in all species. Generally, sulfur cinquefoil flowers are a lighter, sulfur color compared to the deeper yellow of the natives. Sulfur cinquefoil will also show more flowers than the natives, which may only have one or two. Another clue to look for is the size and number of leaves on the flower stem. Sulfur cinquefoil leaves are larger, more abundant, and show a palmately compound pattern. Most native cinquefoils show few leaves on the flower stem, and they tend to be smaller.
Seeds are small and dark colored. If you look closely with a magnifying lens you will see a pattern of lines on the seed coat of sulfur cinquefoil which will not be present on the natives. If you are not sure, collect a plant specimen and take it to the Flathead County Weed Dept. for identification. For more information, check out the War on Weeds website at http://mtwow.org/sulfur-cinquefoil.htm.
Article adapted from “The Explorer” the official newssletter of the Lewis & Clark Conservation District.