My vote for best all-round aquarium plants are members of the genus Ceratopteris ("Sarah-top-tur-is"). They live, floating or rooted in an amazingly wide range of conditions, doing most everything all live plants can do for you, taking up nutrient, making shade, habitat and food,... and they're beautiful.
For folks who lament "live plants don't, won't live for me"; the water sprites are sure winners. Even if you have the proverbial "brown thumb", try some Ceratopteris on the surface of your tanks water; you won't be disappointed. Under "normal" conditions these plants outright thrive.
Talk about cultural differences in the hobby! As a boy I was a retail clerk in a Japanese fish store. We used to "slip" a piece of water sprite in with most every fish sale. This little bit of plant life would ensure bacterial inoculation, lessen pollution and provide something worthwhile for the fish to eat! Years later, Alan Willinger, of many innovative products including the best life-like plastic plants the hobby has ever seen encouraged something similar. Selling "used" polyethylene plants out of dealer tanks to serve the bacterial purpose.
Classification & Species of Use To Aquarists:
The five species of Ceratopteris make up the single genus of the family Parkeriaceae, of the true fern groups. These "simple plants" are characterized by their structure and "alternation of generation"; reproducing through a separate spore and gamete producing forms.
Ceratopteris cornutus (BEAUVOIS) LE PRIEUR, 1810
Synonyms:C. thalictroides Pteris cornuta P. BEAUVOIS.
Natural Distribution & Ecology:Tropical Africa.
Physical Description:The most common "water sprite", or floating fern. This is the new (newer?) name for the old C. thalictroides; a name now applied only to a much more finely and narrow-lobed species. The fronds of C. cornutus are more "horn-like" as the name "cornutus" implies, i.e. thicker and wider.
Ceratopteris thalictroides (LINNAEUS) BRONGNIART, 1821
Indian fern, Sumatra fern, water hornfern.
Synonyms:Acrostichum thalictroides LINNAEUS.
Natural Distribution & Ecology: The tropics of America, Africa, Asia, and northern Australia.
Physical Description:Whether rooted or free-floating, with distinctive deeply lobed, pinnate "leaves" (actually fronds as these plants are ferns)
Ceratopteris pteroides (HOOKER) HIERONYMUS, 1905
Synonyms:Parkeria pteroides, C. cornuta, C. thalictroides f. cornuta
Natural Distribution & Ecology: Tropics of the world.
Physical Description:The common name, floating water sprite, is apropos; this species is best grown totally floating where it's full, rounded-lobed fronds can gain most light.
Pests, Parasites, Disease:
By all appearances, Ceratopteris is quite palatable (humans eat it); all semi-herbivorous fishes nibble on it, as do snails. Thankfully it is a fast grower.
Ceratopterisspp. can be grown rooted, but excel as floating forms. Please do try at least some free material, keeping it thinned to prevent over-shading of plants below.
Rooted plants should be anchored with the portion of the attached rhizome above the gravel; placed below it may rot.
Water sprites are quite variable in their growth and appearance depending on light, and other conditions. Planted ones are more finely pinnately lobed and lighter green in color.
Substrate/Soil:Though Ceratopteris derive their most nutrients through their leaves, some peat and clay as soil in their substrate is beneficial.
Light/Lighting (intensity, spectrum, duration): Moderate to bright illumination, 10k-25k lumens at plant level, 12 hours/day.
pH, KH, Other Chemical:Relatively non-touchy to wide ranges in water chemistry. Soft to slightly hard water (2-15 DH); acidic to medium alkaline pH (6.5-7.5).
Temperature Range:C. thalictroides from the mid seventies to low eighties; the other species listed to same highs, but down to mid sixties F..
Species Kept With:These useful plants may be kept with most every other type of vegetation. If allowed to bunch up on the surface the lower light requiring species (e.g. Cryptocorynes) are suggested.
Trimming:Keep an eye out that your water sprite/floating ferns are not taking over the surface of their tank. As older, planted individuals turn brown and give rise to floating young, you may want to replace them with their offspring.
Either through adventitious roots or "splitting" off plantlets at the leaf edge; only rarely through spores. For maximum production, young plants with three-plus fronds may be broken by hand from mature leaves.
You need only purchase one or a few specimens; easy to grow and propagate.
So you don't have fancy schmancy lighting, carbon dioxide infusion, soil additives, test-kits galore... you can still be a successful aquatic gardener with Ceratopteris.
Anon. 1975. Water plants; water sprite. Aquarium Digest Intl. 3:2(1975).
Brunner, Gerhard. 1973. Aquarium Plants. T.F.H. Publications, NJ. 159 pp.
Randall, Karen A. 1994. Ferns and mosses for the aquarium. AFM 12/94.
Rataj, Karel. 1980. CERATOPTERIS, a common aquarium fern. TFH 4/80.
Rataj, Karel. 1983. Floating water sprite. TFH 7/83.
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.
Stodola, Jiri. 1967. Encyclopedia of Water Plants. T.F.H. Publications, NJ. 368 pp.
1) Ceratopteris cornuta floating in an aquarium; defined as C. thalictroides in older literature. That name now applies only to a plant with much more finely divided fronds.