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What goes around definitely does come around. After a career of doing my best to eradicate the water weeds in the sedge family Cyperaceae, here I am doing my best to help folks grow one of their genera in aquariums!
Hairgrass, or spike-rush, with its thread-like leaves, and rapid growth from throwing out runners, makes an easy addition to cool to tropical tanks, even brackish. As we've often seen, a critical key to success is selecting species that fit into your systems thermal regime. With Eleocharis, the species usually offered are warm water, but there are cold water ones too.
Classification & Species of Use To Aquarists:
To lake managers, the family of Eleocharis ("Ell-ee-oh-car-iss"), the Cyperaceae ("Sigh-purr-ay-see-ee") are akin to fleas on dogs; to be avoided if possible, eradicated if not. Most of the 150 or so species are problematical weeds... worldwide; bog plants clogging waterways from the arctics to the tropics.
The grass-like plants of the Cyperaceae are better known by their more common name, sedges. The whole family is characterized by creeping rhizomes, three-sided stalks and an inflorescence composed of a series of scales; each one subtending an individual flower (drawing). For pondscapers, this family includes several important members (e.g. Cyperus alternifolius, the umbrella plant, the many papyrus species).
Happily some of the smaller perennial members of the genus Eleocharis are good for aquarium use, especially striking as clustered foreground or accent groupings.
Eleocharis acicularis (LINNE) ROEMER & SCHULTES,1817
Synonyms:Heleocharis acicularis, Scripus acicularis, S. chaeta, S. radicans, Eleocharis radicans, E. rivularis, et al..
Natural Distribution & Ecology: Worldwide with the exception of the tropics. Temperatures from the sixties to low eighties F.
Physical Description:Thin (1/32") leaves 4-10 inches tall underwater (2-3 inches in terrestrial/bog applications), without apical plantlets. The thin stalks growing in small bunches of two to sixteen; with many roots
Eleocharis vivipara LINK 1827
Natural Distribution & Ecology: Southeastern U.S.
Physical Description:Called "umbrella grass" for its habit of producing young plantlets at the tips of its leaves; leaves 16-24 inches long, 1/8" thick.
Eleocharis minima KUNTH 1837
Natural Distribution & Ecology: South & Central America, tropical Africa. A cooler water species than the similar E. vivipara; temperatures to the low seventies.
Physical Description:Thread thin (1/32") leaves, 8-12 inches in length (underwater grown), often with adventitious plantlets growing at their tips.
Eleocharis parvula (ROEMER & SCHULTES) LINK 1827
Natural Distribution & Ecology:North American coasts, Cuba, Europe, Africa.
Physical Description:Needle like leaves 2-3 inches long, with tiny rosettes of leaves at their joints. A great plant for creating a lawn-like effect.
Pests, Parasites, Disease:
Algal overgrowth can be a big problem here. Take care to keep lighting, nutrient availability and the needs of desiraable plant material in balance.
Place small groups an inch or more apart to allow for fill-in with lateral runners. To stimulate growth and reproduction, occasionally thin stands and replant.
Substrate/Soil:Mineral clay and peaty loam-rich soil mixed with finer gravel.
Light/Lighting (intensity, spectrum, duration): 20-30k lumens.
pH, KH, Other Chemical:For all species, acidic to slightly alkaline water (pH 6.0-7.2), to mild hardness (KH to 10).
Temperature Range:Per the species. Tropicals: to low 80's. Of those listed all but E. minima.
Species Kept With:Other light-loving species such as Sagittaria, Vallisneria, Echinodorus. Also mix well with crypts.
Trimming:Cutting, pulling of brownish, dying material, replanting of healthy bunches.
Mostly asexual by separating batches that have grown in by way of runners and for viviparous species, separation of plantlets on leaf axils and replanting.
Plants can be made to flower by removing to damp soil conditions. Blossoms are small egg-shaped spikes on squarish stem (illustration). Fruits as achenes; with deep grooves.
Take care that new plants do not have crushed stems, nor that they have started to rot; a sign of unrecoverable loss.
So similar to grasses that you have to check for their three-sided stalks and flowering parts to tell them apart, the sedge genus Eleocharis has much to offer an aquarist looking for a fast, forest-green cover or accent clumping. Provided plenty of light and soil nutrient the hairgrasses are of tremendous utility to the aquarium gardener.
Baensch, Hans A. & Rudiger Riehl. 1993. Aquarium Atlas, v. 2. BAENSCH, Germany. 1212 pp.
Brunner, Gerhard. 1973. Aquarium Plants. T.F.H. Publications, NJ. 159 pp.
James, Barry. 1986. A Fishkeeper's Guide To Aquarium Plants. Salamander Books, U.K.. 117 pp.
Rataj, Karel. 1977. Aquarium plants; hair grass. TFH 12/77.
Riehl, Rudiger & Hans A. Baensch. 1987. Aquarium Atlas, v. 1. MERGUS, Germany. 992 pp.
Roe, Colin D. 1967. A Manual of Aquarium Plants. Shirley Aquatics, England. 111 pp.
Stemmermann, Lani. 1981. A Guide to Pacific Wetland Plants. U.S. Army Corps of Engineers, Honolulu. 118 pp.
Stodola, Jiri. 1967. Encyclopedia of Water Plants. T.F.H. Publications, NJ. 368 pp.
1) An aquarium shot of the most common variety of hairgrass Eleocharis acicularis
2) A public domain illustration showing the salient physical characteristics of the family Cyperaceae.