Flora Feature: Yellow False Foxglove (Aureolaria)

By Jessie Wingo, Center for Urban Habitats

Yellow False Foxglove

Aureolaria spp.

Family: Orobanchaceae

 

A couple weeks ago, while working as a trail technician for the Albemarle County Parks Department, I was tasked with checking out the trails at Walnut Creek Park [Central Virginia] to ensure they were safe and usable. I’d been walking through an area of the park where the forest was dominated by oak and pine in the overstory, and dense colonies of mountain laurel in the shrub layer. The canopy was dense, and light was limited on the forest floor. But as I made my way towards a ridge top, the forest began to open up as the larger trees started to thin, that’s when I noticed bright yellow tubular flowers right next to the trail. The plants were striking, standing out against the fallen leaves and pine needles that covered most of the forest floor. Especially impressive, the vibrant flowers didn’t look the slightest bit stressed by the dry ridge top, or our current drought conditions..this, thanks to an interesting adaptation.

Aureolaria laevigata, photo by Jessie Wingo

Aureolaria, also known as Yellow False Foxglove, or Oak-Leach, are a genus of plant characterized by their yellow tubular flowers and interesting association to Oak trees. Aureolaria spp. are described as being partially parasitic on members of the white oak group, hence the common name “Oak- Leach.” The plants are chlorophyllous and can photosynthesis, but receive some water and nutrition from Oak trees. Aureolaria spp. possess modified root organs called haustoria, which function similar to a feeding tube and attach directly to the Oak roots. This hemiparasitic behavior allows Aureolaria spp. to inhabit dry acidic, infertile soils.

Aureolaria virginica, photo by Jessie Wingo

Four species of Aureolaria have been documented as occurring in Virginia: A. flava (Smooth Yellow False Foxglove, Smooth Oak-Leach), A. pedicularia (Fern-leaf Yellow False Foxglove, Annual Oak-Leach), A. laevigata (Entire-leaf Yellow False Foxglove, Appalachian Oak-leach), and A. virginica (Downy Yellow False Foxglove, Downy Oak-Leach). These species are found in much of eastern U.S states, but are limited in their geographic range within individual states by a preference for specific habitat conditions. In Virginia, these species are most often found in the mountains and outer piedmont. Aureolaria spp. prefer dry upland forests and woodlands dominated by oak. Though plants are said to tolerate a wide range of soil conditions, they are most abundant in areas with strongly acidic, infertile soils. In each of the cases where I’ve seen this plant, members of the Heath family (e.g., Blueberry and Mountain Laurel)—indicators of acidic soils—were found growing nearby. A. laevigata was the species I discovered on the ridge top at Walnut Creek. And earlier this year, during a run in mid-July, I’d seen several colonies of A. virginica growing along sections of a roadcut in the western portion of the county—growing along side thickets of blueberries (Vaccinium spp.) and in close proximity to several large white oak trees (Quercus alba).

Not only do the bright yellow flowers attract various pollinators, the specific species of A. pedicularia and A. flava are host plants to Pyrrhia aurantiago, the Aureolaria Seed Borer Moth. Adult moths lay eggs on the plant in summer which develop into larvae chew that feed on the seed capsules. I’m hoping to get back out to Walnut Creek in the next week or two to check for evidence of the larvae.

Photograph at top: Aureolaria laevigata by Jessie Wingo