It is butterweed season and the fallow fields and roadside ditches are a mass of yellow. Packera glabella is a native plant for most of North America east of the Rockies and for the next few weeks these yellow flowers will be everywhere.
Even though it is a north American native, this winter annual, or biennial member of the Asteraceae family is a troublesome weed for farmers. It favors damp, open fields and often covers the disturbed ground from edge to edge. The bright yellow flowers sit atop the hollow stems in showy clusters, but be warned, each small plant is capable of producing hundreds of seeds which are capable of spreading via the wind, like many of its relatives. Low-till or no-till farmland is especially favorable for seed distribution and germination.
Butterweed is considered toxic to grazing animals such as cattle and sheep and care should be taken to remove it from their pastures, however deer have the good sense to avoid it. Wild turkeys tend to gather in the blooming fields, but it is unknown whether they enjoy the flowers or are eating the insects that are attracted to the flowers. Liver damage is reported in animals that consume quantities of this plant, but most abstain after a taste or two. The real danger lies when farmers harvest hay that contains Packera glabella. Animals eat the hay mixture unknowingly or out of hunger. Humans find this plant as unpalatable as livestock but since it has a similar appearance to various wild mustards, please be confident of your plant's identity if you plan to eat it.
There does not seem to be any folk medicine or herbal lore connected to butterweed. The fact that it's toxic isn't really an issue, as early peoples used a number of plants that we would avoid today. Given the fact that it is so plentiful and is one of the first plants to bloom in the spring makes its avoidance a mystery. I did find one reference that butterweed was used as a treatment for rheumatism, however there are a number of plants using this common name and I couldn't verify that the butterweed that they were using was Packera glabella.
Packera glabella does provide much needed nourishment to honeybees just emerging from their winter rest, and many other insects and bees depend on the pollen as well. Actually, butterweed pollen is a favorite food of mosquitoes. Male mosquitoes eat pollen exclusively, while female mosquitoes partake of pollen along with their protein-rich blood meals so they can produce eggs.
Butterweed grows well in damp, sunny areas and prefers disturbed ground, such as plowed fields and vacant lots. Seeds sprout in late fall and early winter and the leaves form a rosette that maintains viability through the winter. Cold weather causes the leaves to turn purple and they remain that way until temperatures warm in the spring. They can even survive short periods of flooding. The hollow stems shoot up as days grow longer and the yellow flowers burst into bloom a few weeks before the last frost date.
If you grow butterweed in your garden, treat it like an annual and once the blooms fade remove from your garden before it sets seeds. This prevents unwanted spread of an already invasive plant.