There is a plant out there in the Ranunculaceae family known as buttercup. Buttercup can come in many forms whether it is an annual, biennial, or even perennial it can be a major detriment to livestock in pasture fields. I was in a May stroll a few days ago when I noticed a bright yellow flower with 2-3 lobed leaflets with deep clefts.
I did what any good Ag Educator would do and snagged up a good sample (roots, leaves and flowers) to key out on my front porch. On a side note, the best time to key a plant is when it is in bloom so that blooming time is available to you.
I identified it as Ranunculus caricetorum also known as the marsh buttercup. This plant does well in low woods, swamps, marshes, and poorly drained areas like around water springs. Buttercup is a toxic plant in pastured areas if animals ingest it fresh.
Buttercup grows aggressively in patches and has a corm base. Corms are essentially compressed bulb like bases that store a lot of food reserves and thus make this plant hard to get rid of through mowing alone. I will say that mowing and preventing the plant from going to seed will help keep it from spreading however.
The toxin that this plant produces is called protoanemonin. This toxin is oil based and found in the fresh plant stem, it causes irritation and blistering of the skin, lining of the mouth and digestive tract. Fortunately, if buttercup is baled and dried in hay the toxin becomes inert and will not irritate the livestock. To livestock, the plant is bitter and animals will avoid eating it. If the plant overtakes a field however it can become a problem if livestock do not have anything else to eat, especially during the summer months of slow forage growth.
Buttercup is sensitive to most broadleaf selective herbicides used in pastures such as 2,4-D and dicamba products. It also grows in clusters so spot-treatments are a good way to get it under control.