Rare Species Guide

  Synonyms

Athyrium thelypterioides

  Basis for Listing

Deparia acrostichoides (silvery spleenwort) is common and widespread in temperate forests of northeastern North America; however, occurrences drop off precipitously west of the Mississippi River. Considering the geographic and climatic position of Minnesota, it is not surprising that D. acrostichoides is limited to the six southeastern-most counties (Goodhue, Wabasha, Olmsted, Winona, Fillmore, and Houston). Within these six counties, there are also ecological constraints that confine this plant to sensitive and localized forest habitats. Such habitats are found only in the deep stream-dissected terrain of the Blufflands Subsection. Human activities in these habitats including logging, livestock grazing, and residential development can leave lasting changes to the detriment of D. acrostichoides. Given the species’ restricted range in the state, as well as its dependence on exceedingly rare and fragmented habitats, D. acrostichoides was listed as a species of special concern in 2013.

  Description

The fertile and sterile leaves of D. acrostichoides look similar and can reach 80 cm (31 in.) in length. The leaf blade is broadest near the middle, becoming narrow at the base and apex. The blade is divided in a pinnate-pinnatifid pattern, giving it a symmetric “lacy” look. The smallest divisions of the leaf, termed “pinnules”, are linear-oblong in shape and have entire margins. The sori, the small structures associated with spore production, are elongate, straight or slightly curved, and lie along the veins on the lower surface of the leaves.   

In appearance, D. acrostichoides looks most like Athyrium filix-femina, a common species widely known as “lady fern”. An easy way to tell them apart is to look at the smallest segments of the leaf blade, the pinnules. The margins of the pinnules of D. acrostichoides are entire; those of A. filix-femina are serrate.

  Habitat

In Minnesota, D. acrostichoides is strongly associated with north-facing slopes in mesic deciduous forests, especially those forests dominated by Acer saccharum (sugar maple) and Tilia americana (basswood) (Southern Mesic Maple-Basswood Forest). Suitable slopes are often formed of talus, giving them a rocky aspect. Soils developing between and among the rocks are usually loams, particularly silty or sandy loams, though D. acrostichoides is usually rooted in thick humus that accumulates over the soil. These conditions result in a moist and well-aerated rooting environment.

  Biology / Life History

Deparia acrostichoides is a relatively large leafy fern, with the same basic biology of all ferns. It does not produce flowers or seeds but reproduces by spores, which are dispersed by the wind. The structures associated with production of the spores are termed the sori and are normally scattered on the underside of the leaf. In any given year, many or even most of the plants in a population of D. acrostichoides will not produce spores or sori. Annual spore production is apparently not necessary, since individuals are perennial and spread short distances by the growth of horizontal underground rhizomes (Kato 1993). The growth of rhizomes often results in loose colonies of up to several dozen or more individual plants.

  Conservation / Management

Based on field observations in Minnesota, D. acrostichoides has rather specific habitat requirements. A fairly narrow range of shade, temperature, soil moisture, and soil texture must be maintained in order to sustain a stable population. Meeting these requirements is one of the ecosystem functions provided by a healthy forest. Natural disruptions such as those caused by wind storms, ice storms, drought, or deluge are transient events, easily ameliorated by natural processes. Generally, no human intervention is needed. More serious damage, such as removal of the forest canopy, can have long-lasting effects. Opening of the canopy dries the soil, reduces the duff layer, damages the soil biota, and shifts the competitive balance to species more tolerant of dry soil. One study in southern Indiana found that on mesic forested slopes, D. acrostichoides was one of the species that decreased significantly when larger openings were created by logging (Jenkins and Parker 1999).

  Best Time to Search

Deparia acrostichoides can be identified by characteristics of the mature leaf, which is usually present from early June through September. The presence of reproductive structures (indusia and sori) may aid identification and can be most reliably seen during the months of July and August.

  References and Additional Information

Jenkins, M. A., and G. Parker. 1999. Composition and diversity of ground-layer vegetation in silvicultural openings of southern Indiana forests. The American Midland Naturalist 142(1):1-16.

Kato, M. 1993. Deparia. Pages 254-255 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York, New York.

Masahiro, K. 1993. Deparia. Pages 254-255 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New york, New York.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 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.

Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.