Nuttallanthus canadensis (L.) D.A. Sutton
Old Field Toadflax
Basis for Listing
Nuttallanthus canadensis (old field toadflax) is widespread in the eastern half of North America, being relatively common in the southern and eastern coastal states. It seems to become increasingly rare moving inland and, in spite of its name, it occurs in only a small portion of Canada. Habitats in Minnesota are limited to scattered locales in the southeastern and east-central counties, specifically where past glacial processes left thick deposits of sand exposed at the surface (The Blufflands, St. Paul-Baldwin Plains and Moraines, and Anoka Sandplain subsections) and where human activities have minimally disturbed the native vegetation. These requirements considerably narrow the possibilities for N. canadensis to occur in the state. Field studies and analysis of historical trends have detected a pattern of habitat loss and contraction of range; hence, it was listed as a special concern species in 2013.
Nuttallanthus canadensis is a slender plant, reaching a maximum height of about knee-high. The flowers are arranged in a terminal raceme, up to 20 cm (8 in.) long. Each flower is up to 1.25 cm (0.5 in.) long and consists of a green calyx and a blue corolla. The calyx has 5 short pointed lobes, and the corolla has 2 divisions or “lips”. The upper lip has 2 rounded lobes, pointing upwards; the lower lip has 3 rounded lobes, pointing forward. There is a slender nectar spur at the back of the flower. The fruit is a small and dry capsule, with numerous (often more than 100) small angular seeds. The flowering stem has short narrow entire leaves that grow stiffly upwards. There may be short prostrate non-flowering shoots at the base of the flowering stem.
The habitat of N. canadensis in Minnesota consists of dry and sandy soil in prairies, barrens, dunes, and savannas. The soils, even where left undisturbed, are rather fragile and highly erodible. That is, the soil has few roots and little organic material to hold it in place, though there may be lichen colonies on the surface that provide some stability. Because of the fragility of the soil, there are always microsites with patches of bare soil, which is where N. canadensis is usually found.
Biology / Life History
Both cleistogamous and chasmogamous flowers are produced in a single raceme of N. canadensis. Cleistogamous flowers are, by definition, self-pollinating and, in this case, produce smaller capsules and fewer seeds than those of the potentially out-crossing chasmogamous flowers. However, even the chasmogamous flowers of N. canadensis are self-compatible and often self-pollinated (Crawford and Elisens 2006). This indicates that insect pollinators are not needed for seed production, even though insects, particularly bumblebees and other long-tongued bees, have been observed seeking nectar from flowers of N. canadensis.
The root system of N. canadensis consists of a stout taproot that survives only one or perhaps two years. Therefore, this plant can be considered an annual or a biennial and spreads only by seed. The seeds are small and can be blown some short distances by the wind, though they have no specialized structures to aid wind-dispersion. They may also be moved about by small birds or small mammals that feed on or cache the seeds.
Conservation / Management
Available evidence indicates that populations of N. canadensis can withstand a certain amount of soil disturbance within its native habitat. This is not surprising given the fragile and loose texture of the sandy soil for which this species is well-adapted. Natural disturbance likely occurs in the form of localized wind or water erosion, especially following a wildfire, which might expose the soil surface to the elements. This disturbance regime may benefit the plant by exposing buried seeds or reducing competition. It is much more difficult to evaluate the effects of human disturbance on populations of N. canadensis. Clearly, any disturbance that removes all, or a significant portion, of the native vegetation such as conversion to agricultural uses, mining, or road building can be expected to result in the eventual loss of the population. Although individual or small groups of N. canadensis have been observed to survive in habitat fragments, they are likely to be more vulnerable to competition from non-native invasive plants.
Best Time to Search
The best time to search for N. canadensis is during the brief period when flowers are present, from about the middle of May until the middle of June. The leaves are usually shed in mid-summer, but the stems and fruits usually remain until the end of summer.
Welby Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Crawford, P. T., and W. J. Elisens. 2006. Genetic variation and reproductive system among North American species of Nuttallanthus (Plantaginaceae). American Journal of Botany 93(4):582-591.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.
Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.
Minnesota Department of Natural Resources. 2009. Map of Minnesota's remaining native prairie 100 years after the public land survey.
NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.
Robert W. Freckmann Herbarium. 2009. Flora of Wisconsin: Consortium of Wisconsin Herbaria [web application]. University of Wisconsin, Stevens Point. <http://wisflora.herbarium.wisc.edu/>. Accessed 24 June 2009.
Wovcha, D. S., B. C. Delaney, and G. E. Nordquist. 1995. Minnesota's St. Croix River Valley and Anoka Sandplain:a guide to native habitats. University of Minnesota Press, Minneapolis. 248 pp.