Selaginella kraussiana (Kunze) A.Braun 'Frosty Fern'
Frosty fern · Krauss spikemoss · African club moss
- Family
- Selaginellaceae
- Native to
- Southern and eastern Africa
- Habit
- Creeping lycophyte
Where it comes from
Southern and eastern Africa. It has travelled very successfully since — Kew’s introduced list runs to Britain, Ireland, Belgium, the Netherlands, Germany, Czechia and Slovakia, and New Zealand.1
New Zealand is where it has done real damage, and the record there is unusually complete. First collected in 1919, at Pākaraka in the Bay of Islands, having been introduced as an ornamental.234 It is now on the 2020 National Pest Plant Accord, which prohibits its sale, distribution and propagation and makes it an unwanted organism under the Biosecurity Act,5 and the Department of Conservation lists it as an environmental weed. The mechanism is specific: it forms thick forest-floor mats that reduce species richness and suppress native seedlings.4 And the route that should concern a houseplant owner is named outright — nursery potting mix and shop plants.6 This is the third plant on this site banned in New Zealand.
Naming and description
It is not a fern. It is a lycophytelycophyteA member of the older of the two surviving lineages of vascular plants, separated from ferns and seed plants for roughly 410 million years. Spikemosses and clubmosses are lycophytes; nothing sold as a fern is.Glossary — class Lycopodiopsida, order Selaginellales — and ferns and lycophyteslycophyteA member of the older of the two surviving lineages of vascular plants, separated from ferns and seed plants for roughly 410 million years. Spikemosses and clubmosses are lycophytes; nothing sold as a fern is.Glossary are the two surviving lineages of vascular plants, separated for around 410 million years.78 It is not a moss either.
The clean diagnostic is the spores, and it is a genuine one. Spikemosses are heterosporousheterosporousMaking two sizes of spore — a few large ones and many small ones — rather than one. It is the clean way to tell a spikemoss from a fern, most of which make one size.Glossary: megasporangia holding about four large megaspores of 200-600 µm, microsporangia holding more than a hundred microspores of 20-60 µm.8 The family the holly fern belongs to is homosporousheterosporousMaking two sizes of spore — a few large ones and many small ones — rather than one. It is the clean way to tell a spikemoss from a fern, most of which make one size.Glossary — one kind of spore, full stop.9 Worth a small qualification, because the tidy version of this is slightly wrong: most ferns are homosporousheterosporousMaking two sizes of spore — a few large ones and many small ones — rather than one. It is the clean way to tell a spikemoss from a fern, most of which make one size.Glossary, but the water ferns are heterosporousheterosporousMaking two sizes of spore — a few large ones and many small ones — rather than one. It is the clean way to tell a spikemoss from a fern, most of which make one size.Glossary too.1011
Its “roots” are not roots but rhizophores, arising from the branch axils along every prostrate stem and branching dichotomously.12 Which explains both why a fragment roots so readily and why it resents being lifted.
‘Frosty Fern’ is a selling name. A patent search for the exact phrase returns nothing, a separate search of Selaginella patents returns only pharmaceutical and transgenic-oilseed filings with no cultivarcultivarA plant selected and propagated by people rather than described from the wild. Written in single quotes after the species — Monstera deliciosa 'Thai Constellation' — and never italicised.Glossary among them, and a trademark search finds no mark of that text.131415 So: not registered, not patented — and not a fern, which makes the name wrong twice.
What the white tips actually are, nobody has written down. I looked: NC State’s full record has no cultivarcultivarA plant selected and propagated by people rather than described from the wild. Written in single quotes after the species — Monstera deliciosa 'Thai Constellation' — and never italicised.Glossary, no variegationvariegationPatches of leaf with little or no chlorophyll, so they read as white, cream or yellow. The pale tissue cannot feed itself, which is why a variegated plant grows more slowly than a plain one.Glossary and no mention of white tips; the Flora of North America says only that the species “is frequently cultivated and has several cultivarscultivarA plant selected and propagated by people rather than described from the wild. Written in single quotes after the species — Monstera deliciosa 'Thai Constellation' — and never italicised.Glossary” and names none.1617 This page will not call it variegationvariegationPatches of leaf with little or no chlorophyll, so they read as white, cream or yellow. The pale tissue cannot feed itself, which is why a variegated plant grows more slowly than a plain one.Glossary, because nothing supports that.
Fun facts
- It is not a resurrection plant, and confusing it with one will kill it. Several Selaginella genuinely survive complete desiccation and revive — lepidophylla, pulvinata, tamariscina, brachystachya.18 This is not one of them: three literature searches turned up no desiccation or drought study of kraussiana at all, and what exists on it is rhizophore development, sperm ultrastructure and New Zealand weed biology.1920 For this one, dry is dead.
- Its reputation for being delicate is the wrong diagnosis. It is usually described as unforgiving and doomed within weeks of the garden centre, and no source above a blog says that. What the weed literature says is close to the opposite: it “tolerates hot or cold, and light to deep shade, but requires reasonably damp to wet substrate”.6 A plant that has naturalisednaturalisedGrowing and reproducing outside cultivation in a place it is not native to, without help. Three plants in this collection are naturalised somewhere, and banned there for it.Glossary across northern Europe and New Zealand is not fragile. It has one specific intolerance — dry air and a drying substrate — and a heated room supplies exactly that.
- The ASPCA page that covers it is filed under a third wrong name. Look for “Club Moss”: its scientific-name field reads Selaginella kraussiana, and it is non-toxic to dogs, cats and horses.21 Not a moss, not a fern, filed under moss.
Care
- Light
- Shade to deep shade. It tolerates a remarkable range of light and a remarkable range of temperature; what it does not tolerate is drying out.
- Water
- Permanently damp. This is the whole of it. The substrate should not dry, and the species is not one of the resurrection spikemosses — for this one, dry is dead.
- Humidity
- High. No source publishes a percentage for the genus, and I am not going to borrow the fern figures and relabel them. The documented failure is specific: dry air gives brown, shrivelled foliage.
- Temperature
- Tolerant — a weed in cool-temperate Britain, Ireland, Germany and New Zealand, so the hardiness tag of zones 11-12 that circulates is not a physiological limit. Ordinary room temperature is fine.
- Substrate
- A fine, moisture-retentive mix that will not dry out. Shallow, since it creeps rather than roots down.
- Fertilizer
- No tier 1-3 source gives any feeding guidance for the genus. This record does not invent one.
- Propagation
- Division, or simply pinning a stem down — it roots from rhizophores all along its length.
- Dormancy
- None documented, and the evidence points to there being none.
- Common problems
-
- Brown, shrivelled foliage from dry air — the single documented failure mode
- A substrate allowed to dry, which it does not recover from
- Resenting being lifted or disturbed, since it roots along the whole stem rather than from one crown
- Do not put it on a compost heap or let it escape outdoors in a mild climate: it forms thick forest-floor mats that suppress native seedlings, and nursery potting mix is a named route for spreading it