Selaginella kraussiana (Krauss's Spikemoss, Trailing Spikemoss, Mat Spikemoss, African Clubmoss, Garden Selaginella)
Selaginella kraussiana
Table of Contents
Introduction & Discovery
Selaginella kraussiana is the most widely cultivated spikemoss in the temperate world and one of the most recognisable lycophytes in horticulture, familiar to glasshouse growers, terrarium enthusiasts, and garden designers alike. First formally described by the German botanist Gustav Kunze in 1844 from material collected in the Cape region of South Africa by the traveller Christian Ferdinand Friedrich von Krauss, whose surname the specific epithet commemorates, the species has travelled from its Afromontane origins to become a cosmopolitan ornamental. It belongs to Selaginellaceae, the single family of the order Selaginellales, and is not a true fern at all but a member of the lycophyte lineage, phylogenetically closer to Lycopodium and Isoetes than to Polypodium or Asplenium. The distinction matters biologically: Selaginella is heterosporous, producing two different kinds of spores (large megaspores and small microspores) in separate sporangia borne on quadrangular strobili, a reproductive mode found elsewhere in living pteridophytes only in Isoetes. Each microphyll carries a minute ligule on its adaxial base, a flap of tissue absent in the superficially similar Lycopodium and diagnostic of the family. The creeping stems root at intervals by means of rhizophores, leafless peg-like organs unique to the genus that arise at branch angles and differentiate into roots on contact with substrate. In cultivation Selaginella kraussiana forms dense emerald-green mats rarely taller than 2 to 3 centimetres, spreading indefinitely as a living carpet over moist shaded ground, around pond margins, beneath tree ferns, and across the floors of cool greenhouses. Terrarium and bottle-garden culture has sustained its popularity for more than a century and a half; the golden-foliaged cultivar Aurea and the dwarf Brownii have been staples of conservatory horticulture since the Victorian glasshouse boom. Yet the same ecological aggressiveness that makes it a reliable ground cover has turned it into one of the most problematic plant invaders of cool moist forests in New Zealand, the British Isles, and parts of Australia, where it smothers the bryophyte and seedling-fern communities of the forest floor and is classed as a banned noxious species under national biosecurity law.
Discovery & Naming
The genus Selaginella was established as a segregate of Lycopodium by the French botanist Palisot de Beauvois in 1804 and formally circumscribed in his Prodrome des cinquième et sixième familles de l'Aetheogamie of 1805; the name derives from a diminutive of the earlier genus Selago. Selaginella kraussiana was described as new to science by the German botanist Gustav Kunze in 1844 in his Analecta pteridographica, based on material collected in the eastern Cape region of South Africa by the natural historian Christian Ferdinand Friedrich von Krauss during his African travels of 1838 to 1840, and Kunze commemorated the collector in the specific epithet. Krauss's collections, deposited in the Stuttgart Natural History collections, formed the basis of several new plant descriptions from southern Africa in the 1840s. The species entered European horticulture rapidly after its description; it was grown at Kew and at Continental botanic gardens by the 1850s, and was a routine component of Victorian conservatory ground cover and Wardian-case plantings by the 1860s. The cultivars Aurea and Brownii appeared in the horticultural trade later in the nineteenth century, with Brownii commemorating the Scottish nurseryman Robert Brown (one of several gardeners of that name, not the famous botanist). Nineteenth- and early twentieth-century pteridological monographs including those of Spring, Hieronymus, and Alston incorporated S. kraussiana into the broader global treatment of Selaginella, placing it in the section Stachygynandrum. Twentieth-century anatomical and developmental studies treated kraussiana as a model for rhizophore biology; it was among the species used by Wochok and Sussex in their influential 1970s experiments on rhizophore determination. The first molecular phylogenies of Selaginella in the early twenty-first century, based on chloroplast rbcL and nuclear markers, placed kraussiana comfortably within section Stachygynandrum and confirmed its distinctness from the Asian and American ornamentals with which it had been loosely grouped.
Native Range & Distribution Map
Distribution map showing the native range of Selaginella kraussiana.
Biology & Frond Morphology
Selaginella kraussiana belongs to the genus Selaginella in the family Selaginellaceae, producing evergreen, prostrate, mat-forming lycophyte producing freely branched leafy stems rather than true fronds. main axes creep horizontally, rooting at intervals via colourless rhizophores (leafless root-bearing organs diagnostic of the genus) and branch pseudo-dichotomously into flattened, frond-like sprays. the stems are clothed in four ranks of small single-veined microphylls: two lateral rows of larger obliquely-spreading ovate leaves and two dorsal rows of smaller appressed ovate-acuminate leaves, giving the stem a flattened dorsiventral appearance. each microphyll carries a minute membranous ligule on its adaxial base, diagnostic of selaginella versus the superficially similar lycopodium. foliage is bright fresh green to yellowish-green, never the iridescent blue of s. uncinata or s. willdenowii. reproductive structures are small, lax, quadrangular strobili bearing heterosporous sporangia. fronds that unfurl from coiled fiddleheads (croziers). Like all ferns, it reproduces via spores borne on the underside of fertile fronds rather than flowers and seeds, and its life cycle alternates between a dominant sporophyte (the visible plant) and a small, short-lived gametophyte stage.
Reproduction & Propagation
Propagation of Selaginella kraussiana can be achieved through several methods:
- Spores: Collect ripe spores from the underside of fertile fronds, sow on sterilised peat or peat/perlite mix. Do not cover. Keep humid and in bright indirect light. Prothalli (gametophytes) typically develop in 4–12 weeks, and young sporophytes appear after a further 2–6 months.
- Division: Mature clumps with multiple crowns or creeping rhizomes can be divided in spring as new fronds emerge.
- Rhizome cuttings / offsets: Epiphytic genera (Davallia, Polypodium, Phlebodium) can be propagated from 5–10 cm rhizome segments with at least one frond and visible roots.
Cultivation & Substrate
Successful cultivation of Selaginella kraussiana depends on matching three conditions to its natural habitat: consistent moisture without waterlogging, a humus-rich yet well-drained substrate, and the correct light level for its frond type — whether dappled woodland shade, bright filtered light, or, for a handful of rock ferns, direct sun.
Substrate: A light, friable, acidic, organically-rich yet free-draining medium is ideal. A reliable blend is two parts peat or coco coir, one part fine orchid bark or composted pine bark, one part horticultural perlite, and a small handful of charcoal granules per litre. For outdoor plantings amend existing loam with leaf mould and composted bark to a depth of 15 to 20 centimetres. Sterilised substrate is preferred for terrarium use. Slightly acidic, pH 5.0 to 6.5. The species tolerates down to pH 4.5 without visible stress but becomes progressively chlorotic above pH 7.0 and should not be grown on strongly alkaline or calcareous soil. Where garden soil is alkaline, amend with acidic peat substitute, composted pine needles, or elemental sulphur. Good drainage with steady moisture retention. The substrate must never become anoxic or waterlogged around the rhizophores, but it must also never dry through. A perlite component of roughly 20 percent provides pore space; terrarium containers need a drainage layer of 2 to 3 centimetres of horticultural grit or LECA beneath the substrate to collect surplus water. Low to moderate fertility is sufficient. Selaginella kraussiana is an oligotrophic species of Afromontane forest floors and resents salt-rich or strongly fertilised substrates. A quarterly application of very dilute balanced liquid fertiliser (one quarter of recommended strength) during the growing season is adequate for potted plants; outdoor mats are self-sustaining on the slow release of nutrients from leaf litter. High. The species thrives on a substrate dominated by partially decomposed organic material such as leaf mould, composted bark, or peat substitute, which mimics the humus-rich layer of its native forest-floor habitat. Annual top-dressing of outdoor mats with a thin layer of fine leaf mould sustains vigour and prevents opening of the mat by mineral-soil exposure.
Water: Rainwater or soft tap
Light: Bright shade to moderate filtered light is optimal. The species evolved on forest floors and stream banks beneath closed canopy where direct solar radiation is largely excluded, and it performs best in cultivation under 70 to 90 percent shade or beneath a high deciduous canopy. Under north-facing or east-facing exposures it tolerates brief early-morning sun. Full afternoon sun in summer causes rapid scorching, bleaching of the microphylls to pale yellow-brown, and eventual collapse of the mat. Deep shade is well tolerated but produces leggier stems with wider internodes. Indoors the plant succeeds in a position 1 to 2 metres from a lightly curtained east or north window, or beneath a fluorescent or LED lamp providing 100 to 200 micromoles per square metre per second of photosynthetically active radiation for 12 to 14 hours daily. Grow-light supplementation is helpful through temperate winters. Abrupt transfer from shade to stronger light produces characteristic papery yellow-brown patches that do not recover.
Humidity: See species profile
Common Mistakes to Avoid
The single most common fatal mistake is allowing the substrate or ambient air to dry out. A single forgotten weekend of watering during hot weather can brown an entire mat, and drought-damaged stems recover only from protected buried nodes if they recover at all. A second frequent error is siting the plant in too much direct sun; even a few hours of unfiltered summer sun will bleach the foliage irreversibly. A third mistake is using hard tap water, which deposits calcium carbonate on the stems and raises substrate pH into a range the species dislikes; switch to rainwater or filtered water where tap supplies are hard. A fourth mistake is planting into heavy, compacted, poorly-drained clay, which causes rhizophore and basal rot; the substrate must be friable and organic-rich yet free-draining. A fifth is piling mulch over the creeping stems rather than around them; buried growing tips rot. A sixth is neglecting ventilation in sealed terraria, producing a stagnant humid microclimate that fosters Botrytis and bacterial stem rot; a daily crack of the lid is essential. A seventh is selecting the species for naturalising in cool moist woodland where it will escape and become invasive; confine it to contained situations in such climates. An eighth error, particularly in garden design, is assuming the foliage will be the iridescent blue of S. uncinata; kraussiana is always green or gold, never blue.
Seasonal Considerations
Spring (March to May): active growth resumes in outdoor and greenhouse plantings as temperatures rise; remove any winter-damaged tissue, top-dress with leaf mould or fine compost, and resume regular watering. Re-pot indoor specimens if pot-bound, and take stem cuttings during the first flush of new growth when they root most readily. Summer (June to August): maintain constant moisture and humidity; outdoor plantings in Mediterranean climates may need daily watering in hot weather. Shield from afternoon sun and from hot drying winds. Indoor terraria benefit from a slightly increased airflow and occasional light misting during heatwaves. Autumn (September to November): growth continues but slows; reduce feeding and watch for fungal patches as temperatures cool and humidity rises. Clear leaf litter that smothers the mat. Collect strobili now for spore propagation if desired. Winter (December to February): outdoor plantings in zones 7 and 8a benefit from a loose cover of bracken, straw, or conifer branches to moderate hard frost; keep crowns unsmothered once the weather settles. Indoor plants need reduced watering and no fertiliser; supplement light with a grow lamp if winter sun is weak. Avoid placing terraria against cold glass where condensation freezes on internal surfaces.
Diseases & Pests
Common issues affecting Selaginella kraussiana in cultivation:
- Root/rhizome rot: Caused by waterlogged substrate, compacted soil, or overwatering in cool weather. Ensure the growing medium is well-aerated and never let pots sit in standing water for prolonged periods.
- Fungal leaf spot & Botrytis: Brown or grey blotches appear in stagnant, overly humid conditions. Improve air circulation, remove affected fronds, and avoid wetting foliage late in the day.
- Scale insects & mealybugs: The most common fern pests, hiding on stipes and frond undersides. Wipe off with a cotton swab dipped in diluted isopropyl alcohol, or treat with horticultural soap. Many chemical pesticides scorch fern fronds — always test on one frond first.
- Spider mites: Fine webbing and stippled fronds, common in dry indoor air. Raise humidity and rinse fronds regularly with tepid water.
- Frond browning (tip burn): Caused by dry air, direct hot sun, fluoridated or chlorinated tap water (especially in Nephrolepis, Calathea-loving filmy ferns), or soluble-salt build-up from fertiliser. Flush the pot with rainwater and reduce feeding.
Indoor Growing & Terrariums
Selaginella kraussiana can be grown indoors as a houseplant or terrarium subject when its humidity and light requirements are met.
Indoor Setup
- Light: Bright indirect light — an east- or north-facing window, or 30–60 cm under an LED grow light (10–12 hours/day). Most ferns scorch in direct midday sun.
- Humidity: 50–80%. Group plants, stand pots on a pebble-and-water tray, or run a humidifier; misting alone rarely raises ambient humidity enough.
- Temperature: 16–24°C (60–75°F) for most indoor species; avoid cold drafts and hot radiators.
- Substrate: Peat-free potting mix with added perlite and orchid bark for drainage; epiphytic genera (Platycerium, Davallia) grow best mounted on bark or in a bark-heavy orchid mix.
- Water: Keep consistently moist but never waterlogged. Let the top 1–2 cm of substrate dry slightly between waterings in winter.
- Air circulation: A gentle fan discourages fungal leaf spot without drying out the fronds.
Landscape & Garden Use
Selaginella kraussiana can be used in the garden wherever its hardiness and habitat preferences are matched. Ferns are classic choices for shaded borders, woodland gardens, stumperies, rockeries, stream-side plantings, and ground-cover under trees.
Landscape Tips
- Companions: Hostas, Astilbe, Heuchera, Tiarella, Epimedium, hellebores, snowdrops and other shade-tolerant perennials are classic partners.
- Soil preparation: Incorporate leaf mould or composted bark to improve moisture retention and mimic a forest floor.
- Mulching: A 3–5 cm mulch of chipped bark or leaf litter protects the rhizomes, conserves moisture, and slowly releases nutrients.
- Watering: Establish new plantings with regular deep watering during the first growing season; most hardy ferns need only occasional supplemental irrigation once established.
Conservation & Collector Notes
In its African native range Selaginella kraussiana is common, widespread, and not of conservation concern; it is not listed on the IUCN Red List or in regional red-data books. The species is abundant across Afromontane forest habitats from the Cape to Ethiopia and shows no evidence of population decline. The conservation dimension of S. kraussiana is inverted relative to most ornamentals: the problem is not protection of the plant but protection of ecosystems from the plant. In New Zealand the species is listed under the National Pest Plant Accord and its sale, distribution, and propagation are banned; Department of Conservation land managers invest substantial effort in controlling kraussiana infestations in native forest reserves, where it smothers bryophyte turf and fern gametophytes. In the United Kingdom the species is recognised as a non-native invasive in damp woodlands of Ireland, Cornwall, western Scotland, and the Azores, and is included in non-native-species watch lists; planting advisories caution against use in sensitive moist woodland settings. In Australia it is recognised as environmentally weedy in Tasmania and parts of coastal New South Wales and Victoria. In Hawaii it is naturalised in upland wet forest and is considered a threat to native bryophytes and endemic ferns. Responsible cultivation confines the plant to contained terraria, glasshouses, or enclosed garden situations from which vegetative fragments cannot escape into adjoining natural habitat.
Collector Notes
For the serious Selaginella collector S. kraussiana is a foundational species whose variability is worth exploring systematically. The type form has bright mid-green foliage and vigorous spreading habit. The cultivar Aurea (also sold as Gold Tips) has bright chartreuse to golden-yellow foliage, brightest in moderate light and fading toward pale lime under deep shade; it is slightly less vigorous than the type. The cultivar Brownii forms compact rounded cushions 5 to 10 centimetres across with tightly packed foliage and is a staple of terrarium and miniature-landscape plantings. Provenance variation within wild populations is less studied than the ornamental clones but likely reflects the genuine Afromontane range from the Cape to Ethiopia; documented wild-provenance accessions are held at a handful of botanic gardens including Kirstenbosch and the Royal Botanic Garden Edinburgh. Because of the species' ease of vegetative propagation, collectors have little difficulty exchanging material, although border biosecurity regulations in New Zealand and some other jurisdictions strictly control import. Ethical collecting practice obtains material from reputable nurseries or fellow growers rather than from wild native-range populations, and takes special care to prevent accidental release of fragments into natural habitat where the species could naturalise. Collectors in invasive-risk countries should double-bag waste material for landfill or high-temperature composting rather than dispose of it in open green waste. Maintaining labelled pots of the principal cultivars alongside the wild type makes a compact and educational mini-collection occupying no more than a single bench or terrarium.
Ethnobotany & Cultural Significance
Ethnobotanical documentation for Selaginella kraussiana is relatively modest compared to East Asian resurrection Selaginellas. In parts of southern Africa the plant is reported in local ethnomedical literature as an ingredient in preparations for skin complaints, wounds, and minor respiratory ailments, typically used as a decoction or topical poultice of the whole plant. These uses are documented in regional ethnopharmacology surveys but have not entered any official pharmacopoeia and are not recommended as a modern remedy. Phytochemical investigations have identified from Selaginella species a class of unusual dimeric compounds collectively called selaginellins, first isolated from Asian species and subsequently reported across the genus; flavonoid biflavonoids such as amentoflavone and related biflavones are also characteristic of the family. Some of these compounds show antioxidant, anti-inflammatory, and cytotoxic activity in laboratory studies, although clinical validation is limited. Western horticultural ethnography is more substantial: S. kraussiana has been a fixture of Victorian and Edwardian glasshouse and stove culture since the mid-nineteenth century, figuring prominently in illustrated manuals on ferneries and Wardian cases; its use as a lawn-substitute ground cover under glass is documented in garden literature from the 1870s onward. Contemporary biomimetic research uses the genus as a model for understanding lycophyte morphogenesis and rhizophore biology, while conservation and invasion-biology literature treats kraussiana as a case study in the unintended consequences of the ornamental plant trade.
Frequently Asked Questions
My Selaginella kraussiana has gone completely brown after a weekend away — is it dead?
Almost certainly it is severely damaged and parts are unlikely to recover, but the plant is often not entirely dead. Cut back all visibly brown stems with sterile scissors, rehydrate the substrate slowly by standing the pot in a tray of rainwater for an hour, then place the plant in a closed propagator or clear plastic bag at 18 to 22 degrees Celsius in bright shade and maintain saturation for two to three weeks. Surviving buried nodes and sheltered rhizophores frequently resprout new green shoots within this period. If no regrowth appears after a month, the plant has died and should be replaced; save any surviving green fragments as cuttings.
Is the golden-foliaged form Aurea a separate species or a cultivar?
Aurea is a cultivar of Selaginella kraussiana, not a separate species, and is taxonomically identical at the species level to the ordinary green form. The golden colour results from reduced chlorophyll expression and enhanced visibility of accessory pigments, and it is a stable clonal feature maintained by vegetative propagation. Aurea grows a little more slowly than the type and shows its brightest colour in moderate light; in deep shade it reverts toward pale lime green, and in excessive sun it bleaches to straw yellow. Treat it culturally exactly as the type form.
Can I grow Selaginella kraussiana as a lawn substitute in shade?
In a small sheltered shaded area within zones 8 to 10 and in climates where the species is not invasive, yes, and historic Victorian glasshouse practice used it precisely this way. Practical limitations are serious: the mat tolerates no foot traffic, dries out within hours in hot weather without irrigation, is confined to shade, and needs acidic moist soil. In New Zealand, the British Isles, parts of Australia, and Hawaii, such use is strongly discouraged or illegal because of invasive potential. A good compromise in safe climates is to use kraussiana as a ground cover in contained beds around ornamental pots, beneath tree ferns, or in a shaded fern glade, where its beauty is enjoyed but its spread is controlled by hard edges.
Why has a black slimy patch appeared on my terrarium kraussiana?
Black slimy patches indicate bacterial soft rot or Botrytis associated with stagnant humidity, usually after a period of overwatering or insufficient ventilation. Remove the affected tissue with sterilised scissors, along with a generous margin of apparently healthy stem, and discard. Improve airflow by propping the terrarium lid ajar for several hours each day, reduce watering frequency, and allow the top few millimetres of substrate to dry between waterings. If the rot has spread through the entire mat, strip the terrarium back to the drainage layer, discard the old substrate, sterilise glass and hardscape, and start again with fresh medium and healthy cuttings. Prevent recurrence by avoiding stagnant sealed culture.
Is it legal and ethical for me to grow Selaginella kraussiana in my country?
Legality depends on jurisdiction. In most of continental Europe, North America, and tropical Asia the species is a routine ornamental sold without restriction, and home cultivation is entirely lawful. In New Zealand it is listed under the National Pest Plant Accord and sale, propagation, or distribution is prohibited; existing plantings should be contained and ideally replaced with native alternatives. In parts of the United Kingdom and Ireland it is not banned but is formally listed as an environmental weed of concern, and responsible growers avoid planting it in gardens adjoining sensitive moist woodland. In Hawaii and parts of Australia similar caution applies. Ethical practice is to check local biosecurity advice, confine the plant to pots, terraria, or enclosed glasshouses, and never discard fragments into green waste or natural habitat.
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Quick Reference Summary: Selaginella kraussiana
Golden Rule: Match moisture, light and humidity to each fern’s natural habitat — woodland ferns need shade and humus, rock ferns need drainage, filmy ferns need constant humidity.
Selaginella kraussiana, Krauss's or Trailing Spikemoss, is an evergreen mat-forming lycophyte of Afromontane origin, described by Gustav Kunze in 1844 from Cape material collected by C.F.F. von Krauss. Belonging to Selaginellaceae and not to the true ferns, it exhibits the diagnostic lycophyte features of microphylls, a minute ligule on each leaf, rhizophores, and heterosporous strobili producing both megaspores and microspores. Creeping stems branch pseudo-dichotomously into flattened frond-like sprays clothed in four ranks of small green microphylls, rooting at intervals to form emerald carpets ideal for shaded woodland, pond margins, terraria, and greenhouse floors. It prefers bright shade, constant substrate moisture, acidic humus-rich soil, high humidity, and temperatures of 15 to 24 degrees Celsius, and is hardy in USDA zones 7 to 10. The cultivars Aurea (golden) and Brownii (dwarf cushion) are horticultural staples. Propagation is trivially easy by division and stem cuttings. Outside its native range the species is a serious invasive weed in New Zealand, parts of the British Isles, Australia, and Hawaii, and should be grown only in confined situations where escape is prevented.