Eriophorum
Eriophorum vaginatum
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Monocots
Clade:	Commelinids
Order:	Poales
Family:	Cyperaceae
Genus:	Eriophorum L.[1]
Type species
Eriophorum vaginatum L.[2]
Synonyms[3]
Heterotypic synonyms Eriophoropsis Palla Leucoma Ehrh. Linagrostis Guett. Plumaria Bubani Plumaria Heist. ex Fabr.

Eriophorum (cottongrass, cotton-grass or cottonsedge) is a genus of flowering plants in the family Cyperaceae, the sedge family. They are found in the cool temperate, alpine, and Arctic regions of the Northern Hemisphere, primarily in the middle latitudes of North America, Europe, and Asia.

Eriophorium species are perennial herbaceous plants that persist by means of underground rhizomes.^[4][5] Stems (called culms) grow singly or in clumps (i.e., cespitose). Both basal leaves and stem leaves are present, although the latter are bladeless in some species. The terminal inflorescence is either a single erect spikelet or multiple spikelets on peduncles of various lengths. In the case of multiple spikelets, the inflorescence is subtended by one or more leaf-like bracts. Individual flowers have 10 or more smooth perianth bristles that greatly elongate and remain attached to the achene during fruiting. The bristles facilitate seed dispersal by wind. In cold Arctic regions, the bristles also serve as insulation by trapping solar radiation and thereby increasing the temperature of the reproductive organs.^[6]

Identification keys often begin with a pair of alternatives that implicitly divide the genus into two mutually exclusive sections:^[4][5][7][8]

• Eriophorum section Vaginata: one spikelet, without involucral bracts
• Eriophorum section Phyllanthela: multiple spikelets (rarely one), subtended by one or more leaf-like bracts

Besides the number of spikelets and the presence of bracts, other characters may be used for identification, including: the length of the uppermost leaf blade relative to its sheath; the number of bracts (0, 1, or more than 1); the length and orientation of the bracts; the length of the peduncles; and the color of the bristles.

In the first edition of Species Plantarum published in 1753, the Swedish botanist Carl Linnaeus established genus Eriophorum by recognizing four species: Eriophorum vaginatum, Eriophorum polystachion, Eriophorum virginicum, and Eriophorum alpinum.^[1][9] In the second edition published in 1762, Linnaeus added a fifth species, Eriophorum cyperinum.^[10] The name Eriophorum L. is the primary generic name in use today.^[3][11] Although the names of some of the species have changed, the number of recognized taxa in genus Eriophorum has remained more-or-less the same since 1994.^[12][13]

In the fifth edition of Genera Plantarum published in 1754 (intended to accompany the first edition of Species Plantarum), Linnaeus referenced the prior work of the Italian botanist Pier Antonio Micheli and the French botanist Joseph Pitton de Tournefort.^[14] In 1729, Micheli described genus Linagrostis, including an illustration of an unidentified plant.^[15] (The plant was later identified to be Eriophorum vaginatum.^[16]) Tournefort coined the French name Linaigrette (Latin: Linagrostis) in 1694,^[17] but his contribution became better known in Europe when his book was translated to Latin in 1719.^[18]

The French naturalist and mineralogist Jean-Étienne Guettard resurrected the pre-Linnaean name Linagrostis in 1750, and again in 1754, but Linagrostis Guett. is regarded as a synonym for Eriophorum L.^[19][20] After Guettard, the name Linagrostis was redescribed by numerous botanists, including John Hill (1756), Johann Gottfried Zinn (1757), and Giovanni Antonio Scopoli (1771),^[21][22][23] but all three published illegitimate names since Linagrostis Guett. takes precedence. Scopoli's description of Linagrostis Tourn. ex Scop. is notable, however, since it is explicitly based on the early work of Tournefort.^[24] The names Linagrostis vaginata (L.) Scop., Linagrostis alpina (L.) Scop., and Linagrostis polystachia (L.) Scop. are synonyms for the corresponding names introduced by Linnaeus in 1753.^[25][26][27]

The Austrian botanist and mycologist Eduard Palla established genus Eriophoropsis in 1896 by segregating Eriophorum virginicum into a new genus.^[28] The name Eriophoropsis Palla is both a synonym for Eriophorum L. and the basionym of Eriophorum subgen. Eriophoropsis (Palla) Raymond, the latter described by the Canadian botanist Louis-Florent-Marcel Raymond in 1954.^[29][30]

As of August 2024, the following species are accepted by Plants of the World Online (POWO):^[3]

The following natural hybrids are also accepted by POWO:

World Flora Online (WFO) accepts all of the above species and hybrids except Eriophorum arcticum.^[11] In addition, WFO accepts Eriophorum × polystachiovaginatum whereas POWO does not.

Of the five species described by Linnaeus in 1753 and 1762, three of the names are no longer in use. Eriophorum polystachion L. is a rejected name,^[32][33] now considered to be a synonym for Eriophorum angustifolium Honck. subsp. angustifolium,^[34] while Eriophorum alpinum L. and Eriophorum cyperinum L. are synonyms for Trichophorum alpinum (L.) Pers. and Scirpus cyperinus (L.) Kunth, respectively.^[35][36]

The Swedish mycologist and botanist Elias Magnus Fries described Eriophorum russeolum in 1836.^[37] Some authors consider Eriophorum russeolum Fr. to be a synonym for Eriophorum chamissonis C.A.Mey.,^[38][39] while others consider the two names to refer to separate species.^{[40][41][42][43]}

In 1942, the American agrostologist and botanist Alan Ackerman Beetle placed the species Scirpus criniger A.Gray into genus Eriophorum.^[44] In 2012, Eriophorum crinigerum (A.Gray) Beetle was segregated into genus Calliscirpus, and so Eriophorum crinigerum is a synonym for Calliscirpus criniger (A.Gray) C.N.Gilmour, J.R.Starr & Naczi.^[45]

In 1957, the Canadian botanist Louis-Florent-Marcel Raymond placed the species Scirpus scabriculmis Beetle into genus Eriophorum.^[46] In 2019, Eriophorum scabriculme (Beetle) Raymond was segregated into genus Trichophorum.^[47] Hence Eriophorum scabriculme is a synonym for Trichophorum scabriculme (Beetle) J.R.Starr, Lév.-Bourret & B.A.Ford.^[48]

The invalidly published name Eriophorum × polystachiovaginatum Beauverd is a synonym for Eriophorum × beauverdii Soó but the latter is unplaced by POWO.^[49]

In 1849, the Swedish botanist and traveller Nils Johan Andersson placed the European species of Eriophorum into two new sections:^[50]

In 1905, the American botanist Merritt Lyndon Fernald placed the North American species of Eriophorum into Andersson's sections as follows:^[53]

Based on phylogenetic analyses, Eriophorum forms a well‐supported clade nested within the genus Scirpus, which suggests the latter is paraphyletic. To resolve this issue, there are at least two options: 1) merge Eriophorum into Scirpus, or 2) split Scirpus into a series of new genera. As of August 2024, there has been insufficient data for a majority of botanists to prefer one option or the other.^[54][55]

Eriophorum virginicum, Eriophorum tenellum, and Eriophorum gracile form a strongly supported clade that is sister to the rest of the genus. The clade is distinguished by having glumes (scales at the base of each flower in a spikelet) with many prominent nerves, whereas the glumes of the remaining species possess a single prominent midnerve.^[56]

Within a weakly supported clade of unispicate species (i.e., species with a single spikelet), Eriophorum russeolum and Eriophorum scheuchzeri form a strongly supported, monophyletic species complex characterized by a rhizomatous habit, up to 7 sterile glumes, and by glumes with well-defined hyaline margins (i.e., with thin, translucent edges). In contrast, in the sister clade to this complex (Eriophorum vaginatum, Eriophorum brachyantherum, and Eriophorum callitrix) each species has a caespitose habit and more than 12 sterile glumes that generally lack clear hyaline margins.^[56]

Eriophorum species are found in the cool temperate, alpine, and Arctic regions of the Northern Hemisphere,^[4][5] primarily in the middle latitudes of North America, Europe, and Asia.

• North America: E. angustifolium, E. brachyantherum, E. callitrix, E. chamissonis, E. gracile, E. scheuchzeri, E. tenellum, E. triste, E. vaginatum, E. virginicum, E. viridicarinatum
• Europe: E. angustifolium, E. brachyantherum, E. chamissonis, E. gracile, E. latifolium, E. scheuchzeri, E. triste, E. vaginatum
• Asia: E. angustifolium, E. arcticum, E. brachyantherum, E. callitrix, E. chamissonis, E. gracile, E. humile, E. latifolium, E. scheuchzeri, E. tolmatchevii, E. transiens, E. triste, E. vaginatum

Preferred habitats include bogs, fens, meadows, and alpine tundra.^{[citation needed]}

Paper and the wicks of candles have been made of its fiber, and pillows stuffed with the same material. The leaves were formerly used in treating diarrhea, and the spongy pith of the stem for the removal of tapeworm.^[57]

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• Fernald, M. L. (1905a). "The North American species of Eriophorum. Part 1: Synopsis of American species". Rhodora. 7 (77): 81–92. Retrieved 20 August 2024.
• Fernald, M. L. (1905b). "The North American species of Eriophorum. Part 2: Notes on the preceding synopsis". Rhodora. 7 (79): 129–136. Retrieved 20 August 2024.
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