Glyceria fluitans

Glyceria fluitans (syns Festuca fluitans, Poa fluitans, Panicularia fluitans), known as floating sweet-grass[1] and water mannagrass, is a species of perennial grass in the genus Glyceria native to Europe, the Mediterranean region and Western Asia and occurring in wet areas such as ditches, riverbanks and ponds.

Glyceria fluitans
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Poaceae
Subfamily: Pooideae
Genus: Glyceria
G. fluitans
Binomial name
Glyceria fluitans

It has a creeping rootstock, a thick stem which rises to one metre. The leaves are long, narrow and pale green, rough on both sides, often folded at the keel which lies on the surface of the water.

The species epithet fluitans is Latin for "floating".[2]


Before the 19th century, the grains were widely harvested in Central Europe and Sweden, and traded as far as England.[3] It was cooked and eaten as gruel.[3]

Flood toleranceEdit

When a shoot is submerged in floodwater there is a strong reduction of diffusion of gases which limits oxygen and carbon dioxide availability.[4] To handle the poor gas exchange while submerged, Glyceria fluitans forms a gas film around the leaves.[5] The gas film allows to increase the gas exchange since the diffusion of gas within the film is rapid.[6] Glyceria fluitans has two kind of leaves: floating leaves and aerial leaves. Floating leaves form a gas film only on the adaxial side, instead aerial leaves form it on both sides.[5] The formation of a gas film is caused from the superhydrophobicity of the leaves, which is provoked by the special structure of the leaves. Indeed, they have a plicate shape with ridges and grooves, on the microscale they have convex papillose epidermal cells forming papillae and three-dimensional epicuticular waxes.[5] A gas film vanishes typically after 2–6 days of submergence because the leaves become hydrophilic.[7] Regarding the beneficial trait of the gas film development, it can be said that Glyceria fluitans through it enhances the gas exchange and therefore the photosynthesis under flood conditions, but it is seen as a short term strategie.[5]

Environmental conservationEdit

Glyceria fluitans is a component of purple moor grass and rush pastures, a type of Biodiversity Action Plan habitat in the UK. This habitat occurs on poorly drained neutral and acidic soils of the lowlands and upland fringe. It is found in the South West of England, especially in Devon.

At the Great Fen, researchers are running trials with Glyceria fluitans in order to assess its physical and financial viability as a crop in wet farming systems.[8] Glyceria fluitans was chosen because it has been consumed by humans for a long time and because of its tolerance to a wide range of growing conditions.[9] This tolerance originates from the fact that Glyceria fluitans is to some extent self-sterile and therefore outbreeding, which allows for adaptation.[10]

Farming techniquesEdit

The use and cultivation of Glyceria fluitans disappeared little by little during the 19th and 20th century due to its long gathering time and the disappearance of wetlands.[11] For these reasons, known farming techniques are old and not very applicable to today's production systems anymore.

Harvest and postharvest treatmentsEdit

Glyceria fluitans is harvested in the second half of June or early July.[11] The maturation and harvest time of Glyceria fluitans were interesting for farmers in the past centuries because it preceded the wheat and rye harvest by 1 month, a period of significant cereal shortage.[11] The grains of Glyceria fluitans were harvested with a sieve at the morning dew. The sieves were described with long handles and only strong people could use them. After the harvest, grains were dried out and grinded in a mortar filled with straw at the bottom so that the shells could be removed.[11] The reasons why Glyceria fluitans grains were harvested at the morning dew are the following: firstly, grains tend to stick better to the sieves when humid. Secondly, the grains of dry plants tend to fall more easily on the ground at the smallest movement causing yield loses.[11]

However, these harvest techniques are not suitable for today's agricultural production and new cultivars through genetic breeding should be developed.[12]


The sowing of Glyceria fluitans takes place in summer. The seeding density is 8 to 12 lbs per acre.[11]

As a foodEdit

Glyceria fluitans grains were popular in Poland, Germany, Hungary and other European countries for their sweet taste and nutrient richness. In Poland, foods containing Glyceria fluitans were pointed out as specialities of the local cuisine. Originally, Glyceria fluitans was used to prepare dishes as sweet cakes, flatbreads, dumplings, with butter or boiled milk, broths and soups, with oriental spices, as well as in sausages as binding additive.[11]

Due to its healthy properties, between the 17th and 18th century, its consume was advised by pharmacopoeias to people with debilitating diseases as well as malnourished young people.[13][14][15][16]


Nutrient contentEdit

100 g of Glyceria fluitans grains (endosperm, ca. 13.5% water content) contain about: 9.69% of protein, 0.43% of total fat, 75.06% of carbohydrate (starch and sugar), 0.21% of dietary fiber and 0.61% of ash. [17]



  1. ^ BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
  2. ^ Archibald William Smith A Gardener's Handbook of Plant Names: Their Meanings and Origins, p. 140, at Google Books
  3. ^ a b Nesbitt, Mark (2005). Prance, Ghillean; Nesbitt, Mark (eds.). The Cultural History of Plants. Routledge. p. 47. ISBN 0415927463.
  4. ^ Colmer, Timothy D.; Winkel, Anders; Pedersen, Ole (2011). "A perspective on underwater photosynthesis in submerged terrestrial wetland plants". AoB Plants. 2011: plr030. doi:10.1093/aobpla/plr030. PMC 3249690. PMID 22476500.
  5. ^ a b c d Konnerup, Dennis; Pedersen, Ole (2017). "Flood tolerance of Glyceria fluitans: the importance of cuticle hydrophobicity, permeability and leaf gas films for underwater gas exchange". Annals of Botany. 120 (4): 521–528. doi:10.1093/aob/mcx083. PMC 5737359. PMID 29059317.
  6. ^ Verboven, Pieter; Pedersen, Ole; Tri Ho, Quang; Nicolai, Bart M; Colmer, Timothy D (2014). "The mechanism of improved aeration due to gas films on leaves of submerged rice". Plant, Cell & Environment. 37 (10): 2433–2452. doi:10.1111/pce.12300. PMID 24548021. S2CID 2699676.
  7. ^ Winkel, Anders; Pedersen, Ole; Ella, Evangelina; Ismail, Abdelbagi M; Colmer, Timothy D (2014). "Gas film retention and underwater photosynthesis during field submergence of four contrasting rice genotypes". Journal of Experimental Botany. 65 (12): 3225–3233. doi:10.1093/jxb/eru166. PMC 4071835. PMID 24759881.
  8. ^ "Water Works | The Great Fen". Retrieved 2021-11-10.
  9. ^ "Wetland Crop Glyceria". Fens for the Future. Retrieved 2021-11-10.{{cite web}}: CS1 maint: url-status (link)
  10. ^ Borrill, Martin (1956). "A biosystematic study of some Glyceria species in Britain". Watsonia. 3: 291–298.
  11. ^ a b c d e f g Luczaj, L. J.; Dumanowski, J.; Koehler, P.; Mueller-Bieniek, A. (2012). "The Use and Economic Value of Manna grass (Glyceria) in Poland from the Middle Ages to the Twentieth Century". Human Ecology. 40 (5): 721–733. doi:10.1007/s10745-012-9513-4. S2CID 153349412.
  12. ^ Hozyasz, K. K. (2020). "From rediscovered "niche" to "mainstream" - Glyceria fluitans as a candidate grain for manufacturing premium food products". Plants People Planet. 2 (2): 104–106. doi:10.1002/ppp3.10070. S2CID 210312934.
  13. ^ Drobnik, J. (2015). "Polish manna grass in the 16th to 19th centuries: A botanical and medicinal approach (in Polish)". Etnobiologia Polska. 5: 67–87.
  14. ^ Jourdan, A. J. (1840). Pharmacopée Universelle, ou Conspectus des Pharmacopées. Paris, France: J.-B.Bailliére.
  15. ^ Schumacher, C. F. (1825). Medicinsk Plantelære for Studerende Læger og Pharmaceutiker. Kjȍbenhavn: J.H.Schultz.
  16. ^ Stokes, J. (1812). A botanical materia medica consisting of the generic and specific characters of the plants used in medicine and diet, with synonyms, and references to medical authors. London, UK: J. Johnson & Co.
  17. ^ Hartwich, C.; Håkanson, G. (1905). "Über Glyceria fluitans, ein fast vergessenes einheimisches Getreide". Zeitschrift für Untersuchung der Nahrungs- und Genußmittel. 10 (8): 473–478. doi:10.1007/BF02297944.

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