Juncus effusus, with the common names common rush or soft rush, is a perennial herbaceous flowering plant species in the rush family Juncaceae. In North America, the common name soft rush also refers to Juncus interior.
Juncus effusus is nearly cosmopolitan, considered native in Europe, Asia, Africa, North America, and South America. It has naturalized in Australia, Madagascar, and various oceanic islands.
Juncus effusus grows in large clumps about 1.5 metres (4 ft 11 in) tall at the water's edge along streams and ditches, but can be invasive anywhere with moist soil. It is commonly found growing in humus-rich areas like marshes, ditches, fens, and beaver dams.
The stems are smooth cylinders with light pith filling. The yellowish inflorescence appears to emerge from one side of the stem about 20 centimetres (8 in) from the top. In fact the stem ends there; the top part is the bract, that continues with only a slight colour-band marking it from the stem. The lower leaves are reduced to a brown sheath at the bottom of the stem.
- Juncus effusus subsp. austrocalifornicus Lint — endemic to California and Baja California.
- Juncus effusus subsp. effusus — widespread
- Juncus effusus subsp. laxus (Robyns & Tournay) Snogerup — tropical Africa, Madagascar, Mauritius, Canary Islands, Madeira.
- Juncus effusus subsp. pacificus (Fernald & Wiegand) Piper & Beattie — Alaska, British Columbia, Washington, Idaho, Oregon, California, Baja California.
- Juncus effusus subsp. solutus (Fernald & Wiegand) Hämet-Ahti — central and eastern United States.
The species provides wildfowl, wader feeding, and nesting habitats, and also habitats for small mammals. The rootstalks are eaten by muskrats, and birds take shelter amongst the plant's stems. A number of invertebrates feed on soft rush, including the rufous minor moth. 
Juncus effusus is listed as one of the seven ingredients of Hui sup tea. In Japan, this rush is called igusa, and grown to be woven into the covering of tatami mats (the filling is rice straw, extruded styrofoam, chip board, or some combination). In Iran and Afghanistan too it is used to weave light cheap mats. It is called halfa (حلفا) and has medicinal uses too. In Europe, this rush was once used to make rushlights (by soaking the pith in grease), a cheap alternative to candles.
The cultivar Juncus effusus 'Spiralis' (syn. Juncus spiralis), with the common names corkscrew rush or spiral rush, is a distinctive potted and water garden plant due to its very curled spiral like foliage.
Juncus effusus can become a naturalized or invasive species, undesirable in rangelands for its unpalatability to livestock. Suggested methods of controlling rushes include: ploughing; high applications of inorganic fertilizer (can pollute watersheds); and topping to prevent seed formation.
- Kew World Checklist of Selected Plant Families
- Kirschner, J. & al. (2002). Juncaceae. Species Plantarum: Flora of the World 6-8: 1-237, 1-336,1-192. Australian Biological Resources Study, Canberra.
- Al-Qura'n, S. (2011). The flora of Jordan: A taxonomical revision of Juncaceae. Arnaldoa 18: 33-36.
- Flora of China Vol. 24 Page 48, 灯心草 deng xin cao, Juncus effusus Linnaeus, Sp. Pl. 1: 326. 1753
- Flora of North America vol 22, Soft rush, Juncus effusus Linnaeus, Sp. Pl. 1: 326. 1753.
- C. Michael Hogan, ed. 2010. Juncus effusus. Encyclopedia of Life.
- Conservation Land Management Magazine: "Cutting Rushes" article, Spring 2003, British Wildlife Publishing.
- Calflora: Juncus effusus subsp. austrocalifornicus
- Jepson eFlora: Juncus effusus subsp. austrocalifornicus
- Peter F.Zika (2003). "The native subspecies of Juncus effusus (Juncaceae) in western North America". Brittonia. 55 (2): 150–156. doi:10.1663/0007-196X(2003)055[0150:TNSOJE]2.0.CO;2. JSTOR 3218455.
- Calflora: Juncus effusus subsp. pacificus
- Jepson: Juncus effusus subsp. pacificus
- USDA: Juncus effusus subsp. solutus
- Morton, J.K.; Venn, Joan. M. (2000). "The Flora of Manitoulin Island". University of Waterloo Biology Series N. 40. 3rd. edition.
- Niering, William A.; Olmstead, Nancy C. (1985) . The Audubon Society Field Guide to North American Wildflowers, Eastern Region. Knopf. p. 568. ISBN 0-394-50432-1.
- "Structure of Tatami". kyo-tatami.com. Motoyama Tatami Shop. 2015-06-28. Retrieved 14 June 2021.
- Heritage Perennials: Juncus effusus spiralis
- Bhattacharyya (1980). "Structure of effusol: A new phenolic constituent from Juncus effusus". Experientia. 36: 27–28. doi:10.1007/bf02003949. S2CID 41731083.
- Shima, Katsuhito; Toyota, Masao; Asakawa, Yoshinori (1991). "Phenanthrene derivatives from the medullae of Juncus effusus". Phytochemistry. 30 (9): 3149. doi:10.1016/S0031-9422(00)98276-1.
- Carvalho, CF; Sargent, MV; Stanojevic, E (1984). "Phenanthrene synthesis: The synthesis of effusol a 9,10-Dihydrophenanthrene from the marsh grass Juncus effusus". Australian Journal of Chemistry. 37 (10): 2111. doi:10.1071/CH9842111.
- Liao, You-Jiao; Zhai, Hai-Feng; Zhang, Bing; Duan, Tian-Xuan; Huang, Jian-Mei (2010). "Anxiolytic and Sedative Effects of Dehydroeffusol from Juncus effusus in Mice". Planta Medica. 77 (5): 416–20. doi:10.1055/s-0030-1250517. PMID 21104609.
- Calflora Database: Juncus effusus (Bog rush, Common bog rush, Common rush)
- Jepson Manual eFlora (TJM2) treatment of Juncus effusus
- University of Michigan - Dearborn: Native American Ethnobotany of Juncus effusus
- UC CalPhotos gallery of Juncus effusus
- Radoslaw Walkowiak: Short Note of Juncus effusus ssp. effusus (CTC PAPER 2020)
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