How Does Sphagnum Moss Hold Water in Dead Cells?
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How does sphagnum moss hold water in dead cells? Much of its water sits in cells that are no longer alive, which are the moss’s hyaline cells. The short answer is that the leaves of sphagnum contain hyaline cells, which are large, empty, dead cells with pores, and much of the water is stored in those cells and in the spaces between leaves and branches. This explainer walks through the mechanism using two research papers, explains how the cell structure supports it, and lists what the sources do not say.
Quick answer
- Sphagnum leaves contain “large dead empty cells perforated by pores,” which are called hyaline cells.
- The water is held “within dead hyaline cells, outside the protoplasts,” so it is not inside living cell contents.
- Extra water sits in “capillary spaces between branches and leaves” in the moss.
- The hyaline cell walls develop spiral thickenings and pores, and this development includes programmed cell death.
What the moss is made of
A sphagnum shoot has more than one kind of leaf cell. The sources describe leaves that contain living, green cells alongside a second group that is very different. One paper states that sphagnum tissues “consist of large dead empty cells perforated by pores,” and that these cells in the leaves are termed hyaline. The same paper notes that hyaline cells occupy a substantially larger volume than the living chlorophyllous cells around them. The moss depends on both kinds of cell. The green cells carry out photosynthesis, while the hyaline cells work as a reservoir for water.
The arrangement of the whole plant also matters. The same source says that “Sphagnum species have arrangements of shoots, branches and leaves that enable them to conduct and retain water efficiently.” In other words, the water-holding ability is not only a property of single cells. It also depends on how the shoots and branches are packed together.
Why dead cells can hold water
Water usually sits inside living cells, where it mixes with the cytoplasm. Sphagnum works differently. A research paper on desiccation and recovery states that “it is well known that sphagna hold a substantial volume of water within dead hyaline cells, outside the protoplasts.” The protoplast is the living part of the cell, so the water is held in the empty space around it.
The same paper compares sphagnum with succulent plants. It says that “their water is not cytoplasmic but rather is stored in dead hyaline cells.” Because the water is outside the living cell contents, the moss can keep a large store of water without needing the living parts of its cells to hold it. The paper also says that this storage has an effect on how the plant loses water. It states that “the result of containing such water is that turgor only starts dropping at low WCs,” where WCs means water contents. In plain terms, the living cells keep their internal pressure for longer as the moss dries, because the water supply in the dead cells is still available.
The paper describes the strategy as a form of drought avoidance. It describes sphagnum as a classical drought avoider, one that avoids desiccation “by storing a large volume of water.” This is different from a strategy where living cells can tolerate drying. Sphagnum relies on the large store.
How pores and walls support the store
Hyaline cells are not simply empty bags. The second paper, which studies the development of hyaline cells in Sphagnum capillifolium, describes how they change as the moss grows. It says that “some cells lose chloroplasts and form hyaline cells,” and that “these hyaline cells enlarge, develop spiral thickenings, and form water-conducting pores.” The spiral thickenings are part of the cell wall, and the pores connect the cell interior to the surrounding environment, so water can enter and move through the cell.
The same paper describes the process that produces these features. It says that hyaline cells gradually differentiate, “marked by the initiation of secondary wall thickening, pore formation, and programmed cell death.” The phrase programmed cell death explains why the cells are dead when mature. The cell goes through a planned sequence of changes that removes the living contents and leaves the wall and pores in place.
Taken together, these sources describe a structure with three parts. The first is a large empty cell. The second is a wall with thickenings that help keep the cell shape. The third is a set of pores that allow water to enter and move through the cell. The paper on desiccation adds that the water inside these cells is separate from the living protoplast.
Capillary water between leaves and branches
Hyaline cells are not the only place where sphagnum holds water. The desiccation paper divides total water into fractions, and the first fraction is external water. It notes that external water “can probably be divided into two sub-fractions.” One sub-fraction is “excess water held in capillary spaces between branches and leaves that remains after blotting the moss.” The paper therefore describes two places for external water: the spaces between parts of the shoot, and the hollow hyaline cells.
The paper also reports that the proportion of external water varied between species. It says the proportion “was generally higher in hummock species.” This is a detail about species differences, and it shows that the arrangement of the moss affects how much water it holds.
How the structure is built during growth
The development paper follows the moss from spore to mature gametophyte, which is the leafy stage of the plant. It describes four stages in the lab-grown plants: filamentous protonema, thalloid protonema, young gametophyte, and mature gametophyte. The authors say that the morphological changes in the cell walls of hyaline cells, “particularly their increased volume,” distinguish them from the chlorophyllous cells.
The paper also explains why the process is important. It says sphagnum’s “remarkable water retention” depends on these cells, and that the cells are described as “specialized structures with exceptional water retention capacity.” The paper describes these features as central to the moss’s role in wetland hydrology. It does not give a numerical value for how much water a single cell can hold, so the explanation here stays with the structure and the mechanism.
How we chose these sources
The two sources were selected because they are research papers from the PubMed Central archive that deal directly with water in Sphagnum. The first paper covers water content and desiccation. The second covers the development and gene expression of hyaline cells. Both pages returned HTTP 200 when opened with curl on 2026-10-28, and the quotes in this article were taken from the fetched text. No retail or product pages were used.
What we could not verify
The sources explain the structure and the general mechanism, but several questions remain open. The explanation is limited to what the two papers state, and the points below are not covered by them.
What the sources do not say
The sources do not give a single number for the water a dead hyaline cell can hold, and they do not describe the exact size of the pores. They also do not give a field measurement for how fast a sphagnum mat takes up or loses water. The development paper says that future work should examine the candidate genes under stressors such as drought, which means the genetic side of water holding is still being studied. These gaps are noted here so the explanation does not claim more than the sources show.
Frequently asked questions
Are the water-holding cells in sphagnum alive?
The sources describe hyaline cells as dead when mature. One paper refers to “dead hyaline cells,” and the development paper names programmed cell death as part of their formation. The green chlorophyllous cells in the same leaves remain alive and carry out photosynthesis.
Where does the water sit inside the cell?
The water sits in the empty space outside the protoplast. The desiccation paper states that the water is held “outside the protoplasts,” and that it is not cytoplasmic.
What role do the pores play?
The development paper says that hyaline cells “form water-conducting pores.” The pores are part of the structure that lets water move through the cell, and the paper ties pore formation to the same developmental process that produces the thickened wall.
Is all of the water inside the dead cells?
No. The desiccation paper says that external water has two parts, and one part is held in “capillary spaces between branches and leaves.” The paper therefore describes water in both the hyaline cells and the spaces between shoot parts.
Does this explain how sphagnum affects peat bogs?
The development paper links the water-holding cells to the moss’s role in wetland hydrology, and it describes peatlands as carbon sinks. This article does not go further than that link, because the sources do not quantify the effect on any particular bog. For more background on the moss itself, see what peat moss is. For a related plant process that also involves water movement, see how plants refill embolized xylem after drought.
Sources
- Effect of Water Content Components on Desiccation and Recovery in Sphagnum Mosses, PMC2701845. https://pmc.ncbi.nlm.nih.gov/articles/PMC2701845/ (HTTP 200, opened 2026-10-28)
- From spore to gametophyte: Investigating morphological dynamics of hyaline cells and corresponding gene expression patterns in Sphagnum, PMC12144726. https://pmc.ncbi.nlm.nih.gov/articles/PMC12144726/ (HTTP 200, opened 2026-10-28)
