Getting to Know Selaginella: A Terrarium Care Guide

Few terrarium genera carry the evolutionary depth of Selaginella, and few present as wide a variety of forms in cultivation. The genus is the sole member of the family Selaginellaceae and contains roughly 700 described species, making it the largest genus among the lycophytes; this is a plant lineage distinct from both mosses and ferns, and one of the oldest groups of vascular plants still alive today. Selaginella are broadly pantropical in distribution, occupying habitats from deeply shaded rainforest understory to seasonally arid rock outcrops, and they have evolved correspondingly different specializations. Some, including the strikingly blue Selaginella sp. Borneo Blue, produce structural iridescence in their upper leaf cells that scatters blue light through the canopy shade. Others, such as the famous Selaginella lepidophylla, are "resurrection plants" able to desiccate to apparent death and revive within hours of being rewatered. The same genus that supplies these extremes also produces the dense, mossy carpets growers use across the floor of a terrarium, and the practical care for the cultivated species is more accessible than the breadth of the genus might suggest.

Native Range and Habitat

Selaginella is pantropical in the broadest sense, with species present across both Old World and New World tropics and extending into seasonally cool temperate zones at altitude. Major centers of diversity occur across Southeast Asia, including Borneo, Sumatra, Java, and the Philippines, as well as throughout Central and South America and into the Caribbean. A smaller subset of species reaches into the temperate Northern Hemisphere, and a few, with Selaginella lepidophylla among them, are adapted to genuinely arid conditions in the deserts of Mexico and the southwestern United States. The majority of terrarium-relevant species, however, originate in humid lowland and mid-elevation tropical forests, where they colonize the forest floor, mossy banks, decaying logs, and the lower trunks of larger plants.

In these wet-forest habitats, Selaginella receive light only after it has been heavily filtered through several layers of canopy. Ambient humidity is sustained for most of the year, often between 80 and 100 percent, and air movement is gentle rather than persistent. The substrate around the plants tends to be a thin, perpetually damp layer of leaf litter and decaying organic matter overlying mineral soil, providing high moisture availability and good drainage despite the saturated appearance. The drought-adapted species occupy a completely different niche, growing on exposed rocks and in crevices where they tolerate full desiccation between rains; these are not the species growers typically encounter in cultivation.

Are Selaginella Ferns or Mosses?

Selaginella belong to neither group. The genus is placed in the lycophytes, a separate lineage of vascular plants whose fossil record extends back to the Devonian period, roughly 410 million years ago. Lycophytes share with ferns the use of spores rather than seeds for reproduction, but their resemblance to true ferns is superficial; the two lineages diverged from one another well over 400 million years ago, and Selaginella is more distantly related to any modern fern than a fern is to an oak tree. Selaginella also superficially resembles mosses, particularly in cultivated specimens where the dense, scaled foliage produces a moss-like appearance, but mosses are entirely non-vascular plants without true roots or conducting tissue, whereas Selaginella possess both.

Two diagnostic features distinguish Selaginella from both groups. The first is the presence of a small flap of tissue called a ligule near the base of each microphyll, visible only under magnification and unique to this lineage and its extinct relatives. The second is heterospory: Selaginella produce two distinct spore types, microspores and megaspores, borne in cone-like structures called strobili at the tips of stems. This reproductive system bears closer ecological resemblance to that of seed plants than to that of ferns, and it represents one of the earliest examples of the reproductive strategy that would later define the dominant land plant lineages.

Why Are Some Selaginella Iridescent?

A small number of Selaginella species produce a striking blue iridescence on their upper leaf surfaces under low-light conditions; Selaginella sp. Borneo Blue, currently available in our greenhouse, is among the most ornamental of these. The color is not the product of any blue pigment. It arises from precisely spaced multilayered structures within the upper cells of the leaf, which interact with incoming light through thin-film interference and reflect only a narrow band of blue wavelengths back toward the viewer. The mechanism is the same one that produces the iridescent blues of certain beetle wings and butterfly scales; it is structural color rather than pigmentary, and it disappears when the leaf is held against a black background or once the plant dries out.

The functional significance of the iridescence is still under active research. The most commonly cited hypothesis, proposed by Hébant and Lee in 1984, is that the structural color enhances photosynthesis under the dim, red-shifted light of the deep forest understory by selectively transmitting longer wavelengths to the chloroplasts beneath. The trait is largely restricted to species growing in deeply shaded conditions, which lends weight to a photosynthetic role. In cultivation, the blue iridescence of Borneo Blue is best preserved by keeping the species under genuinely low and indirect light; under brighter illumination the color fades and the leaf takes on a more ordinary green appearance.

The Resurrection Selaginella

A separate lineage of Selaginella has evolved an extreme tolerance for drought rather than a preference for shade. The classic example is Selaginella lepidophylla, native to the Chihuahuan Desert of Mexico and the southwestern United States, where it grows on exposed limestone outcrops with no canopy cover and erratic rainfall. The species is capable of losing nearly all of its cellular water, curling into a tight brown ball that appears entirely dead, and then unfurling and resuming photosynthesis within hours of being rewetted. Related species in Asia, including Selaginella tamariscina and Selaginella bryopteris, share the same capability.

The biochemical basis for this resurrection involves the accumulation of trehalose, a sugar that protects cellular structures during desiccation, along with a coordinated suite of dehydration-protective proteins and antioxidant systems that prevent oxidative damage during the dry phase. These species are not typical terrarium subjects; their water and humidity requirements are essentially the opposite of what most growers provide. They are mentioned here primarily to convey how remarkable the genus is in evolutionary terms. The species available to terrarium growers are almost entirely the moisture-loving forest types, and care for these follows a far more conventional path.

Selaginella Terrarium Care

Cultivation of the rainforest-type Selaginella in terraria is straightforward provided the environmental requirements are met. The genus thrives in conditions that mirror its native understory habitat: ambient humidity sustained between 80 and 100 percent, gentle and consistent air circulation, low to moderate indirect lighting, and a substrate that remains evenly moist without becoming waterlogged. High-output lighting will bleach the foliage and, in the case of iridescent species such as Borneo Blue, will diminish or eliminate the structural color that defines the plant's appearance. A position beneath taller companion plants, or in a shaded section of the enclosure, generally produces the best results.

Substrate selection should favor moisture retention with adequate aeration. Sphagnum-based mixes perform well, as does ABG mix supplemented with additional sphagnum. The root systems of Selaginella are fine and shallow; the species establish best in a substrate that maintains consistent moisture while still draining freely. Most cultivated species root readily on top of damp sphagnum and from cuttings placed in direct contact with the substrate, and they will form spreading carpets across the surface of the enclosure if conditions remain consistent. Temperature requirements are forgiving for the majority of species in cultivation; standard tropical conditions between 60 and 80 degrees Fahrenheit are suitable, and prolonged exposure below 50 degrees should be avoided.

Common Selaginella Care Mistakes

The two most frequent issues encountered by growers are insufficient humidity and excessive light. Selaginella foliage dries quickly when ambient humidity falls below the comfort range of the species, and the fine scaled leaves take on a crisp, brown appearance that does not recover. Sustained high humidity is therefore the single most important factor in long-term success. A drying substrate produces the same outcome from the opposite direction; the roots are shallow and unforgiving of complete drying out, even briefly. Excessive light is the second major issue. Selaginella evolved under filtered shade, and direct or high-intensity terrarium lighting bleaches the leaves, suppresses iridescence in species that produce it, and accelerates substrate drying. If color appears washed out or foliage is yellowing, light intensity should be the first variable evaluated and reduced.

Getting Started With Selaginella

For growers approaching Selaginella for the first time, the most reliable starting point is one of the more forgiving forest species established in stable, high-humidity terrarium conditions. Once the plant has settled and begun to spread, observation of how it responds to your particular enclosure microclimate will inform subsequent additions of more demanding species, including the iridescent forms such as Borneo Blue that require the lowest light. Each of our listings includes notes on the individual species and its typical behavior in cultivation. Availability changes regularly, and the link below will reflect what is currently in stock.

Browse all available Selaginella here.

If you are uncertain which species would be most appropriate for your setup, please reach out through our contact page. We are happy to recommend something suited to both your experience level and the conditions you are working with.

Every specimen is personally propagated and tended in our greenhouse in Palm Bay, Florida. Nothing is sourced from outside wholesalers.

- Brandon

References

Banks, J.A. (2009). Selaginella and 400 million years of separation. Annual Review of Plant Biology, 60, 223–238. https://doi.org/10.1146/annurev.arplant.59.032607.092851

Hébant, C., & Lee, D.W. (1984). Ultrastructural basis and developmental control of blue iridescence in Selaginella leaves. American Journal of Botany, 71(2), 216–219. https://doi.org/10.1002/j.1537-2197.1984.tb12509.x

Yobi, A., Wone, B.W.M., Xu, W., Alexander, D.C., Guo, L., Ryals, J.A., Oliver, M.J., & Cushman, J.C. (2013). Metabolomic profiling in Selaginella lepidophylla at various hydration states provides new insights into the mechanistic basis of desiccation tolerance. Molecular Plant, 6(2), 369–385. https://doi.org/10.1093/mp/sss155

Plants of the World Online. Selaginella P.Beauv. Royal Botanic Gardens, Kew. https://powo.science.kew.org/

Encyclopedia of Life. Selaginella. https://eol.org/

Frequently Asked Questions

Are Selaginella hard to care for?

Most cultivated Selaginella are best characterized as moderate. The environmental requirements are not difficult to provide in a closed terrarium: sustained humidity above 80 percent, indirect light, and a substrate that retains moisture without waterlogging. The genus is forgiving of moderate variation in temperature and routine once these conditions are stable. Difficulty increases for the more deeply shade-dependent species, particularly the iridescent ones, where light intensity must be kept low enough to preserve the structural color.

How much light do Selaginella need?

Selaginella require low to moderate indirect light. The genus evolved under filtered shade in rainforest understory, and direct or high-intensity terrarium lighting bleaches the foliage. In iridescent species such as Selaginella sp. Borneo Blue, the blue structural color is suppressed or eliminated under bright illumination. A position beneath taller companion plants, or in a shaded section of the enclosure, generally produces the strongest color and the most natural growth.

What substrate is best for Selaginella?

Sphagnum-based mixes and ABG mix supplemented with additional sphagnum both perform well. The root systems of Selaginella are fine and shallow, and they establish best in a substrate that holds consistent moisture while still draining freely. Most species root readily on top of damp sphagnum and will spread across the surface of a substrate that remains consistently moist. A substrate that dries out fully, even briefly, will stress or kill the plant.

How often should I water Selaginella?

Selaginella require a substrate that stays consistently moist. In a properly closed terrarium with sustained humidity above 80 percent, this often means watering only occasionally; in a more open enclosure, more frequent attention is required. The surface of the substrate should remain damp to the touch at all times. If the foliage appears less rigid than usual or the surface of the substrate begins to dry, it is time to water. Standing water at the base of the plant should be avoided.

Why is my Selaginella turning brown or drying out?

Browning or crisping foliage in Selaginella almost always indicates insufficient humidity, a drying substrate, or both. The fine scaled leaves desiccate quickly once ambient humidity falls below the species' comfort range, and the affected portions do not recover; new growth must take their place. If humidity and substrate moisture are confirmed to be in range, the next variables to check are airflow that is too aggressive and excessive light. Restoring sustained humidity above 80 percent and lowering light intensity will generally allow healthy plants to resume normal growth.