Plants of Concern

Citizen Science Rare Plant Monitoring Program

Tomanthera auriculata

Eared False Foxglove

Tomanthera Auriculata

Illustration by Nancy Klaud

A Case Study

This fall-flowering annual hemiparasite depends on regular fire and disturbance to maintain a foothold in tallgrass prairies.

Family: Orobanchaceae
Life history: Annual
Illinois Status: Rare (not listed)

Populations monitored: 22
Subpopulations monitored: 44
Counties monitored: 5

Introduction

Eared false foxglove (Tomanthera auriculata; synonym: Agalinis auriculata) is a hemiparasitic annual species that depends on dynamic prairie and savannah communities. Where these communities provide patches of open space intermixed with diverse native vegetation, eared false foxglove can thrive.

Habitat & Range

The distribution of eared false foxglove extends from New Jersey west to Minnesota and south to Texas and South Carolina. Occurrences are sparsely scattered across most of this range, with the densest population clusters in the historic eastern extent of the tall grass prairie in Illinois, southern Wisconsin, and Iowa1,10.

Species Biology

Eared false foxglove grows in moist prairies and savannas of the Chicago region but can occur in glades, barrens, and openings in other parts of its range2, 3. Flowering begins in August and the seeds of this species can remain viable for three and a half years4. The species has a unique life history, being both annual and hemiparasitic. By tapping into the roots of nearby plants, it gleans nutrients from plants like black-eyed Susan (Rudbeckia fulgida) and western sunflower (Helianthus occidentalis)5, 6. Hemiparasitic plants don’t tend to kill their host plants and may be important in maintaining diverse plant communities15.

As with many annual plants, population size can fluctuate dramatically from year to year8. However, population size isn’t the only measure of success—flowers must produce seeds for a population to persist. To do this, eared false foxglove doesn’t wholly rely on pollinators. Flowers are able to fertilize themselves, though this helpful ability may come with a cost: the species has lower genetic diversity than more common, closely related species, like purple false foxglove (Agalinis purpurea)8.

Eared false foxglove requires disturbance to germinate and grow through the sometimes dense prairie thatch each year8, 9. As such, it may have been at home along shrub edges and in savannas, where prairies graded into woodlands. These sparsely treed grasslands, now rare in the Chicago region, once burned regularly, producing a patchwork habitat where annual species like eared false foxglove could have found open spaces in which to establish2, 7, 16.

Threats

In Illinois, populations have declined as a result of widespread habitat loss7, but lack of management, barriers to seed germination, and the availability of suitable host plants may also contribute to the rarity of this species8.

Browsing by deer and rodents presents a clear threat to populations of eared false foxglove. In the most dramatic cases, Plants of Concern monitors have found populations with 60-90% of all plants browsed before setting seed. Insect herbivory can also take a heavy toll on populations by reducing seed set11. Black horned tree crickets (Oecanthus nigricornis), verbena bud moth (Endothenia hebesana), and the buckeye butterfly (Junonia coenia) are all major herbivores on eared false foxglove. POC data shows that the intensity of browse and insect damage varies widely from year to year.

Conservation Status

In 1990, the Illinois Endangered Species Protection Board cited habitat destruction, collecting, and other development pressures as reasons for listing this formerly widespread species as threatened. At the time, there were 27 known populations of the species in 18 counties throughout Illinois. Since the original listing, 20 populations and five counties have been added, and delisting has been proposed for 2015.

Monitoring & Research

Plants of Concern began monitoring eared false foxglove at six Illinois locations, comprising a total of ten subpopulations (distinct groupings of plants within a population), in 2001. Since that time, the number of monitored populations has increased by 16, including two monitored populations in Indiana. Demographic monitoring, which involves tagging individual plants and tracking them across a growing season, was conducted by POC in five of these populations over ten years.

Data collected by Plants of Concern has shown that habitat management, specifically removal of woody brush and reduction of deer populations, can improve overall habitat quality as well as helping eared false foxglove populations. However, it is also clear that eared false foxglove can be outcompeted by perennial prairie species. Maintenance of habitat mosaics, where different parts of a habitat provide differing conditions to support a variety of species, is critical to maintaining healthy populations of eared false foxglove13.

Plants of Concern has also seen the clear and direct effect that fire can have on populations of eared false foxglove. After prescribed burning, a necessary management activity used to maintain prairies and savannas, monitored populations of eared false foxglove often increase in number (see graph below).

graph

Impacts

In 2014, eared false foxglove was recommended for delisting in Illinois. It is considered to now be more common than previously thought, or it has experienced some recovery since it was originally listed. This is a significant change, as the species was once under consideration for listing at the federal level, indicating a nationwide concern for its persistence14.

Delisting is a clear step in the right direction, but eared false foxglove remains rare throughout its range and is facing significant challenges such as habitat loss and lack of management. By providing data on population trends, citizen scientists with Plants of Concern support efforts to maintain eared false foxglove habitat in healthy, diverse ecosystems.   

Sources: