Gymnocarpium robertianum
Limestone oak fern
Image of Gymnocarpium robertianum

Photo by Michael R. Penskar 

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Key Characteristics

Small fern (10-50 cm) of dense cedar swamps and limestone outcroppings; leaf broadly triangular, twice-divided, pinnae straight, perpendicular to rachis; underside of leaf and rachis densely covered by short, glandular hairs.

Status and Rank

  • State Status: T
  • State Rank: S2
  • Global Rank: G5


County NameNumber of OccurrencesYear Last Observed
St. Clair11888
Distribution map for Gymnocarpium robertianum

Updated 5/15/2018. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.


This species is found primiarly in northern white cedar-dominated swamps in northern Lower Michigan and the Upper Peninsula, but can also occur in shaded, cedar-dominated limestone glades and shaded limestone cliffs.

Natural Community Types


For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.

Associated Plants

Abies balsamea (balsam fir), Aquilegia canadensis (wild columbine), Aralia nudicaulis (wild sarsaparilla), Asplenium ruta-muraria (wall-rue), A. trichomanes (maidenhair spleenwort), Betula papyrifera (paper birch), Campanula rotundifolia (harebell), Carex eburnea, C. pedunculata, Clintonia borealis (bluebead-lily), Coptis trifolia (goldthread), Cornus canadensis (bunchberry), Cornus rugosa (round-leaved dogwood), Cypripedium parviflorum var. pubescens (large yellow lady-slipper), Cystopteris fragilis (fragile fern), Diervilla lonicera (bush-honeysuckle), Fragaria virginiana (wild strawberry), Galium triflorum (fragrant bedstraw), Gymnocarpium dryopteris (oak fern), Halenia deflexa (spurred gentian), Huperzia lucidula (shining clubmoss), Linnaea borealis (twinflower), Maianthemum canadense (Canada mayflower), Mitella nuda (naked miterwort), Osmunda regalis (royal fern), Pellaea glabella (smooth cliff-brake), Petasites frigidus (sweet-coltsfoot), Polygala paucifolia (gay-wings), Populus tremuloides (quaking aspen), Ribes americanum (wild black currant), Rubus pubescens (dwarf raspberry), Shepherdia canadensis (soapberry), Sphagnum spp. (sphagnum mosses), Thuja occidentalis (northern white-cedar), Trientalis borealis (star-flower), Viola renifolia (kidney-leaved violet).


This species requires the maintenance of hydrology in conifer swamps and protection of groundwater sources. Maintenance of the forest canopy is also likely important to provide continued shade and a cool, moist microclimate.

General Survey Guidelines

Random meander search covers areas that appear likely to have rare taxa, based on habitat and the judgement of the investigator.

Survey Methods

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at [Accessed Aug 18, 2018]

More Information

See MNFI Species Abstract


Survey References

Technical References

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