Rock Spikemoss (Selaginella rupestris): Moss, Clubmoss or Other

During my July 2025 visit to the old, closed Midlothian Asbestos Mine located west of Matachewan, northeastern Ontario, Canada, I saw for the first time the vascular plant named rock spikemoss (Selaginella rupestris; Photo 1). It is also known informally as ledge spike-moss, rock spike-moss, dwarf spikemoss, dwarf spike-moss, festoon-pine, ledge spikemoss, rock selaginella, northern selaginella, bird-nest-moss, and resurrection plant (https://data.canadensys.net/vascan/name/Selaginella%20rupestris; https://www.wildflower.org/plants/result.php?id_plant=SERU).

Its appearance and common names raise the question “is rock spikemoss (Selaginella rupestris) a moss, a clubmoss, or something else?” It is certainly unusual - at least to me.

As an aside, I visited the old minesite to look for any unusual plants that may be serpentinite endemics - plants that are adapted to grow on the harsh serpentinite soil - but more about that below.

Selaginella rupestris is a tiny, evergreen perennial plant that can look like a moss (Photo 2) or miniature clubmoss (Photo 3). Mosses, clubmosses and spikemosses can form dense mats and can grow in moist, shady locations, leading to the common misidentification. In the case of the spikemoss I saw at the Midlothian mine, were it not for the compact size and form of the spikemoss, I likely would have mistaken it for a clubmoss and walked on. However, because it was growing an serpentinite rock substrate, I stopped to look more closely.

Genus and Species:

Spikemosses are part of the order Selaginellales and family Selaginellaceae. As such, Selaginella rupestris is also part of the family Selaginellaceae. The family Selaginellaceae consists of a single genus Selaginella. That genus consists of 700 species. S. rupestris has the widest distribution range of the entire genus (https://www.minnesotawildflowers.info/fern/rock-spikemoss). It occurs widely across eastern North America and at one locality in Greenland (https://en.wikipedia.org/wiki/Selaginella_rupestris). Spikemosses are widely distributed in all parts of the world, particularly in the tropics, where many occur as forest plants.

Plant Form:

Selaginella rupestris is reported to grow in long or spreading mats (Photo 1), or rarely cushion-like mats (Photo 2) (https://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Selaginella%20rupestris&noTransfer=0).

Habitat:

Selaginella rupestris prefers open, dry, sandy or rocky places habitats including rock ledges, grasslands, and meadows (https://floranorthamerica.org/Selaginella_rupestris; https://www.minnesotawildflowers.info/fern/rock-spikemoss; and https://gobotany.nativeplanttrust.org/species/selaginella/rupestris/). I saw it growing on a south-facing serpentinite rock outcrop that was hot and dry (tip of red arrow in Photo 4) and on an open lichen-covered serpentinite knoll that faces north-northeast (Photo 5). Both outcrops will dry out during the summer.

In the absence of water, S. rupestris is reported to roll into a ball, until it comes into contact with water when it reopens (https://en.wikipedia.org/wiki/Selaginella_rupestris); hence, the common name “resurrection plant”.

Selaginella rupestris develops spike-like structures called strobili, located at the branch tips, that contain spores. Spores are released in late summer of early fall (https://www.minnesotawildflowers.info/fern/rock-spikemoss). I saw no strobili on the plants I saw in late July.

Why My Attention:

Selaginella rupestris caught my attention because:

a) it was unusual in form - it just looked different to me;

b) given the serpentinite rock substrate it was growing on, I wondered if it was a serpentine endemic – that is, a plant specifically adapted to hostile chemical conditions found on serpentine soils that are rich in magnesium, copper, nickle, cobalt, chromium, and iron and low in calcium, potassium, nitrogen, and phosphorus; and

c) its form crudely resembled that of ancient gymnosperm clubmoss suggesting the plant I saw in the field might have a lineage that goes back into deep geological time.

Alas, S. rupestris is reported to grow on substrates that range in pH (https://gobotany.nativeplanttrust.org/species/selaginella/rupestris/) and is not considered to be a serpentine endemic.

Paleobotany:

Regarding the lineage, fossil and DNA-based divergence time estimates indicate the genus Selaginella has existed on Earth for at least 100 million years (e.g., Cretaceous) and possible as far back as 300 million years (e.g. Devonian to Carboniferous) (https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.16600). Selaginella rupestris appears to have an old lineage.

COSEWIC Status in Ontario:

In Ontario, Canada, S. rupestris is currently listed as Data Deficient by COSEWIC, meaning there is not enough information available to determine if the species is at risk or not.

What Type of Plant Is Selaginella rupestris?

To answer the title question, Selaginella rupestris is not a moss or a clubmoss, although it may be mistaken as either. It is a spikemoss. That begs the question “what is a spikemoss?”.

A spikemoss is a type of vascular plant that is related to ferns. Spikemosses are seedless and like mosses and clubmosses, spikemosses reproduce by spores. BUT, unlike mosses, spikemosses are vascular plants, which means they have specialized tissues (xylem and phloem) that transport water and nutrients through the plant, like ferns and flowering plants. To repeat, mosses do NOT have vascular tissue.

So, the most important distinction between spikemoss and moss is the presence of vascular tissue in the spikemosses.

Closing Musings:

This was my first encounter with Selaginella rupestris. While not a serpentine endemic, S. rupestris is an interesting, new-to-me vascular plant that reporduces by spores and that has an ancient lineage. Given its superficial resemblance to mosses and clubmosses, I wonder if its presence in northern Ontario may be underestimated because it is easy to miss and overlook.

Aug 2, 2025