Subwassertang
Fissidens-like (round pellia)
easy careOverview
Subwassertang — often written “süsswassertang” and nicknamed round pellia — is an unusual, rootless green plant that is neither a moss nor a true fern, but the gametophyte stage of a fern ally. It grows as loose, translucent green fronds that clump together, and it is genuinely easy: low light, no CO2, no substrate. Because it has no roots, it is tied or wedged onto hardscape like moss, where it forms soft green cushions that shrimp and fry adore. Slow, forgiving and undemanding, it is a lovely low-tech detail plant.
Planting & placement
Subwassertang is attached to hardscape, never planted in substrate — it has no roots to bury. Tie clumps to driftwood or rock with cotton thread or fishing line, wedge them into crevices, or pin them under a piece of mesh until they knit together. Unlike moss it never truly grips the surface, so it relies on being tangled, tied or trapped to stay put. It suits shady spots and the foreground or lower midground, and looks especially good tucked among stones — see how to plant aquarium plants for tying technique and aquascaping for beginners for using it on hardscape. It pairs well with flame moss on the same wood.
Light, CO2 & ferts
Subwassertang is a true low-light plant. Give it low to medium light — strong light gives little extra growth and mainly encourages algae to settle on the fronds, which is very hard to clean off. It needs no CO2. A modest water-column fertilizer is all it wants, since it feeds from the water like moss. Gentle flow through the clump keeps it clean and fed and stops debris collecting inside.
Propagation & problems
Propagation is simple: split a clump into pieces and re-tie or re-wedge them, and each piece grows on. It divides endlessly, so one portion slowly becomes many. The main problems are algae settling on the fronds under too much light, and clumps drifting loose because they have nothing to root into — secure them well and keep light modest. Debris trapped inside a dense clump can rot, so rinse it gently at water changes. Algae on the fine fronds is nearly impossible to remove, so prevention matters — see how to get rid of aquarium algae. Kept dim and secured, subwassertang is a slow, hardy, characterful low-tech plant.
Subwassertang — frequently asked questions
Is subwassertang a moss?
No, though it is treated like one. It is actually the gametophyte stage of a fern (a fern ally, sometimes called round pellia). It has no true roots and grows as loose green fronds, so it is used exactly like moss — tied to hardscape.
Does subwassertang need CO2 or strong light?
Neither. Subwassertang is a low-tech, low-light plant that grows without injected CO2. In fact it prefers modest light — strong light offers little benefit and invites algae onto the fronds, which is hard to remove.
How do I attach subwassertang to wood or rock?
Tie it on with thread or fishing line, or wedge clumps into crevices in the hardscape. It has no roots, so it never grips like moss does — it mainly stays put by being tangled or tied. Many keepers just tuck it between rocks or under mesh.
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