Rare Species Guide

  Synonyms

Gerardia auriculata, Tomanthera auriculata

  Basis for Listing

Agalinis auriculata (eared false foxglove) is a poorly understood species that appears to be rare or infrequent wherever it occurs, even in the center of its range. It is now considered extirpated from a number of states where it once occurred. Only a handful of populations are currently known to exist in Minnesota. All are quite small and occur in vulnerable prairie habitats. The size of these populations varies from one or two individuals to several hundred, but most have fewer than 50 plants. The extent of prairie habitats in southern Minnesota has declined as much as 99% since European settlement (Minnesota's Remaining Native Prairie). Most populations known in Minnesota occur in small habitat remnants on railroad rights-of-way, where their continued existence is uncertain. For these reasons, A. auriculata was listed as endangered in Minnesota in 1984.

  Description

Flowers of A. auriculata are 2.5-5 cm (1-2 in.) long and grow opposite each other on an unbranched flowering stalk. The 5-cleft purple flowers have a pale-pink throat and red-purple spots. The upper 2 lobes are smaller than the lower 3, giving the flower a slightly asymmetric appearance. The fruit is a dry capsule containing numerous small seeds. Mature plants are covered with short stiff hairs. The unbranched 4-angled stems grow from 15-90 cm (6-35 in.) in height. The opposite leaves have a clasping auricle, or ear, from which the species derives its scientific name. It is the only member of the genus Agalinis with a scabrous (rough) stem and auricled leaves.

  Habitat

Early collection records of A. auriculata in Minnesota were from wet meadows in the Minnesota River valley (North-Central Glaciated Plains and Minnesota and Northeast Iowa Morainal sections). Those habitats are largely gone now or have been degraded to the point where they no longer support a significant number of native species. More recent records include prairies, particularly prairie remnants along railroad rights-of-way. These are sometimes classified as deep-soil mesic prairies.

  Biology / Life History

Agalinis auriculata is an annual that germinates in the spring and flowers in August and early September. The earliest documented flowering in Minnesota was on the 12th of August and the latest was on the 4th of September. Most records show clustered flowering during the last few days of August. A study in Illinois (Mulvaney et al. 2004) found that the flowering period for each plant averaged 8 days and, on average, 2 flowers per plant open each day, usually in early morning. Each flower remained receptive for only one day and if not visited by an insect pollinator would self-pollinate, without reduction in fruit set. The same study identified primary insect visitors as the Common Eastern Bumble Bee (Bombus impatiens; Apidae) and the Two-spotted Long-horned Bee (Melissodes bimaculata; Apidae). A study looking at the genetic diversity of A. auriculata concluded that although the species can reproduce by self-pollinating, out-crossing is common and is responsible for maintaining genetic diversity within populations.

Laboratory studies demonstrate that seeds are dormant by October, require cold stratification and light for germination, and can persist in the soil for up to four years (Baskin et al. 1991). The seeds are small and possess no specialized structures for dispersal. It is likely they fall directly from the capsule or are moved short distances by wind. It is also likely that small ground foraging animals may prey on the seeds and inadvertently act as dispersal agents. Seed viability tests in one study in Illinois (Molano-Flores 2007) found germination rates ranged from 68—99 percent.

Agalinis auriculata is reputed to be a hemiparasite, obtaining part of its nutrition from the roots of other plants. Several grasses and composites have been imputed as hosts, but the identity of all possible host plants is not known. Field observations across the range suggest that light and certain soil conditions are limiting factors for this species. However, it is unknown how these factors interact to affect population dynamics.

  Conservation / Management

Because A. auriculata is an annual species and maintains a seed bank in the soil, failure to relocate plants at a site where it was previously documented does not necessarily mean that it has been extirpated from that site. The population may be existing entirely as dormant seeds, waiting for favorable conditions to break dormancy and begin growing. The necessary stimulus is not known but could be provided by animal activity such as gopher digging or ant mound building that might expose the seeds to light. Attempts to artificially stimulate the germination of a buried seed bank have never been successful and could be harmful to the population or habitat. The best approach to management may be to allow natural ecosystem processes to proceed, if such processes are functioning. In small remnant habitats where natural processes may have been compromised, it may be necessary to implement a regimen of spring burns during the dormant season (prior to plants greening up) that would serve to control competing woody vegetation, which can diminish reproduction in affected populations. It has also been reported that grazing by White-tailed Deer (Odocoileus virginianus) can reduce fertility of plants (Vitt et al. 2009). Another factor to consider is the pollinator community. Without a healthy community of suitable pollinators (primarily large bees), the continued survival of a population of A. auriculata cannot be assured.

  Best Time to Search

Agalinis auriculata is visible from spring through October, but the best time to search for this species is during the flowering period in late August and early September.

  Conservation Efforts in Minnesota

In 2000, the Minnesota DNR's Natural Heritage and Nongame Research Program conducted a status survey for A. auriculata, revisiting sites found by the DNR's Minnesota Biological Survey in 1999 and searching an additional 40 sites in eight counties. Results were poor, but because the species can maintain a seed bank, it is possible that it will eventually be found in habitats where it was not found during previous searches. This provides an excellent basis for conservation efforts though, as of 2020 no specific conservation actions had been undertaken.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Baskin, J. M., C. C. Baskin, P. D. Parr, and M. Cunningham. 1991. Seed germination ecology of the rare hemiparasite Tomanthera auriculata (Scrophulariaceae). Castanea 56:51-58.

Molano-Flores, B., J. A. Koontz, and M. A. Feist. 2007. Seed germination of the Illinois-threatened Agalinis auriculata (Michx.) Blake (Orobanchaceae). Castanea 72(2):116-118.

Mulvaney, C. R., B. Molano-Flores, and D. W. Whitman. 2004. The reproductive biology of Agalinis auriculata (Michx.) Raf. (Orobanchaceae), a threatened North American prairie inhabitant. International Journal of Plant Sciences 165(4):605-614.

Pennell, F. W. 1935. The Scrophulariaceae of eastern temperate North America, Academy of Natural Sciences of Philadelphia, Monographs Number 1. Academy of Natural Sciences of Philadelphia, Philadelphia, Pennsylvania. 650 pp.

Rawinski, T. J. 1990. Final status survey report: The distribution and abundance of eared false foxglove (Tomanthera auriculata). Unpublished report submitted to the U.S. Fish and Wildlife Service, Region 5, Newton Corner, Massachusetts. 4 pp.

Sather, N. P. 2000. Interim status survey report for Agalinis auriculata in Minnesota. Unpublished report submitted to the U. S. Fish and Wildlife Service, Twin Cities Field Office, Bloomington, Minnesota.

Vitt, P., K. Havens, B. E. Kendall, and T. M. Knight. 2009. Effects of community-level grassland management on the non-target rare annual Agalinis auriculata. Biological Conservation 142(4):798-805.