Cryptogramma acrostichoides
American rock-brake
Image of Cryptogramma acrostichoides

Photo by Susan R. Crispin 

More Images

Key Characteristics

Small fern (10-25 cm) of sunny, dry rocky shores on Isle Royale; leaves forming tufts of thick, evergreen, dissected fronds; pinnae fan-shaped; fertile fronds taller and narrow.

Status and Rank

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


County NameNumber of OccurrencesYear Last Observed
Distribution map for Cryptogramma acrostichoides

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.


The only known sites are on Isle Royale, on dry, sunny bedrock glades near the Lake Superior shoreline.

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

Red oak, white pine, bearberry, ground juniper, rusty woodsia, pale corydalis, wild rose, bastard toadflax, cranesbill, three-toothed cinquefoil, harebell, and hairgrass.


Requires protection of habitat and perpetuation of natural disturbance regimes. This community occupies a stressed, potentially unstable environment; many of the species found in this community do not tolerate later stages of succession and require management that prevents woody plant encroachment. This species may be vulnerable to excessive foot traffic for colonies located along trails.

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]


Survey References

Technical References

Facebook link