In April, carpets of low-growing prairie wildflowers bloom, taking advantage of sunlight before taller grasses create shade. Among them are two plant species that, in addition to turning sunlight into plant food through good old-fashioned photosynthesis, supplement their nutrient uptake by stealing from neighboring plants.
Both paintbrush (also called painted cup; Castilleja coccinea) and lousewort (also called wood betony; Pedicularis canadensis) have specialized roots called haustoria that work their way into the roots of other plants to literally tap into their water and nutrients. Because paintbrush and lousewort have chlorophyll to produce food on their own, they are not completely parasitic on other plants, but are referred to as hemiparasitic—partial parasites. As with parasitic plants, hemiparasitic plants may have evolved this trait to better thrive in relatively arid and/or nutrient-poor habitats, which some prairies can be.
When walking in a prairie throughout the growing season, you may notice that plants growing amid paintbrush and/or lousewort are shorter in stature than specimens growing away from these two plants. This is likely because these hemiparasites are reducing the vigor of their host plants. This effect creates patches of shorter vegetation in prairies, which can benefit many vertebrate animals that need a variety of prairie vegetation structures.
Genetic research reveals that lousewort, classified within the Scrophulariaceae plant family, within which paintbrushes may also be classified, may be better placed in the Orobanchaceae family with species that are true parasitic plants, lacking green chlorophyll.
Photo above of red paintbrush and yellow lousewort blooming at MPF’s Noah Brown’s Prairie by Bruce Schuette. The blooms of paintbrush and lousewort provide critically important nectar and pollen food sources for many pollinators in spring. The red structures of the paintbrush are not petals but bracts; the yellow tubular structures are the true flowers.
