Rare Species Guide

  Synonyms

Arabis laevigata var. laevigata

  Basis for Listing

Extensive searches of forested habitats in Minnesota have revealed Borodinia laevigata (smooth rock cress) to be quite rare and to be largely limited to the southeastern corner of the state, mostly within the Paleozoic Plateau Section. This species is often associated with a narrow range of environmental conditions that develop on forested ridge tops and slopes as well as cliffs and associated talus. Removal of trees and the invasion of non-native species are the primary threats to the habitat. Given the small number of known populations, as well as the small size of those populations, Borodinia laevigata was listed special concern in 2013.

  Description

The stems of B. laevigata are smooth and 30-110 cm (12-43 in.) tall. The basal leaves are 1-4 cm (0.40-1.6 in.) wide and smooth, with serrate or dentate margins. The stem will have 7-15 smooth leaves, each 3-20 cm (1-8 in.) long, with a clasping base. The inflorescence is a loose raceme, with 16-45 flowers. The petals are whitish and 3-5 mm (0.1-0.2 in.) long; the sepals are about one-half the length of the petals. The mature fruits (siliques) are 5-10 cm (2-4 in.) long, 0.7-2.5 mm (0.03-0.10 in.) wide, and grow generally upwards or outwards, rather than downwards (Al-Shehbaz and Windham 2010).

  Habitat

In general, B. laevigata occurs on slopes in mesic deciduous forests. In most cases, these slopes are composed of talus and occur at the base of cliffs. In some situations, the talus and cliff are absent, or at least not prominent. The essential components of good habitat appear to be shade and mesic or dry-mesic conditions.

  Biology / Life History

Reportedly, B. laevigata can function as a biennial or as a monocarpic perennial. In other words, seedlings exist as a rosette of basal leaves for one or more years; then, at some point, the plant produces a flowering stem and dies (Bloom et al. 1990). While the number of years that an individual remains a rosette is dependent on its size and vigor, it has been reported as between one and seven years (Bloom et al. 2002a). This particular life history is somewhat unusual for a forest species. Biennials and monocarpic perennials are more typically found in open and exposed habitats, where the disturbance cycle is short and severe. This assures the plant a good seedbed, where competition for light, nutrients, and water is minimal. The disturbance regime in the forest habitat of B. laevigata is typically less frequent, less severe, and non-cyclic in nature. One might speculate that soil erosion, resulting from the steepness of the slope, may be the source of disturbance that sustains populations of B. laevigata.

Seeds of B. laevigata are typically shed in autumn and germinate the following spring. A few seeds may remain in the dried seed pod for one or even two years. The majority of seeds are reported to fall within 0.5 m (40 in.) of the parent plants (Bloom et al. 2002b). The seeds possess no specialized structures to aid dispersion; they are likely dispersed by gravity and secondarily by small animals that may cache the seeds.

Borodinia laevigata seeds need cold stratification to germinate, which is accomplished by overwintering on the surface of the ground. A portion of the seeds which do not germinate in the spring can remain viable in a persistent seed bank below the leaf litter (Bloom et al. 1990).

Mortality in a population of B. laevigata was studied at a site in Kentucky (Bloom et al. 2001). Mortality was reportedly high, with a very low percentage of the plants that germinated (less than one percent) surviving to reproduce. Mortality corresponded to low precipitation and high air temperatures. Herbivory was also a source of mortality. Mortality was lower in plants growing on a rock substrate, compared with those on a soil substrate (Bloom et al. 2003).

  Conservation / Management

The steep forested slopes where B. laevigata frequently occurs are prone to soil erosion. Under some circumstances, especially in agricultural and urban settings, erosion can be excessive and is indicative of a problem. It often happens as a result of poorly implemented logging practices, road building, and farming too close to a slope. In well-protected habitats, of the type favored by B. laevigata, erosion is a natural process, and in most cases it does not imply a problem that requires correction. In fact, normal sheet erosion may be the process that maintains the habitat, and any attempt to control normal erosion would be misguided. The invasion of non-native species, especially Rhamnus cathartica (common buckthorn), Lonicera spp. (non-native honeysuckle shrubs), and Alliaria petiolata (garlic mustard) are also of great concern.

  Best Time to Search

The best time to search for Borodinia laevigata is when it is in fruit or flower, usually from about May 5 until August 6.

  Authors/Revisions

Welby R. Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Alexander, P. J., M. D. Windham, J. B. Beck, I. A. Al-Shebaz, L. Allphin, and C. D. Bailey. 2013. Molecular phylogenetics and taxonomy of the genus Boechera and related genera (Brassicaceae: Boechereae). Systematic Botany 38(1): 192-209.

Al-Shehbaz, I. A., and M. D. Windham. 2010. Boechera. Pages 348-412 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexcio. Volume 7. Oxford University Press, New York, New York.

Bloom T. C., C. C. Baskin, and J. M. Baskin. 1990. Germination ecology of the facultative biennial Arabis laevigata variety laevigata. American Midland Naturalist 124(2):214-230.

Bloom T. C., J. M. Baskin, and C. C. Baskin. 2001. Ecological life history of the facultative woodland biennial Arabis laevigata variety laevigata (Brassicaceae): survivorship. Journal of the Torrey Botanical Society 128(2):93-108.

Bloom T. C., J. M. Baskin, and C. C. Baskin. 2002a. Ecological life history of the facultative woodland biennial Arabis laevigata variety laevigata (Brassicaceae): reproductive phenology and fecundity. Journal of the Torrey Botanical Society 129(1):29-38.

Bloom T. C., J. M. Baskin, and C. C. Baskin. 2002b. Ecological life history of the facultative woodland biennial Arabis laevigata variety laevigata (Brassicaceae): seed dispersal. Journal of the Torrey Botanical Society 129(1):21-28.

Bloom T. C., J. M. Baskin, and C. C. Baskin. 2003. Ecological life history of the facultative woodland biennial Arabis laevigata variety laevigata (Brassicaceae): effects of leaf litter cover, herbivory, and substrate-type on bolting and fecundity. Journal of the Torrey Botanical Society 130(1):16-22.

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.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.

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 8 July 2009.