Here we have two members of the least advanced group of true plants, Division Bryophyta, doing their bit for aquarists as prodigious floating or bottom cover, oxygenators, fry refuge, and bubble-nest supporters.
And are they easy to grow? If anything these primitive plants are too easy to keep and propagate; often becoming the "plant that ate Cincinnati" if not kept trimmed back.
Classification & Species of Use To Aquarists:
In the grand scheme of things as plant taxonomists see them, true plants (Kingdom Plantae) derived from green algae long ago. As this story goes, two groups, the non-vascular bryophytes ("bri-oh-fights"), and vascular plants (Division Tracheophyta), branched off from the green algae retaining chlorophyll a and b, and starch as a primary storage food. A major advent of life on land for bryophytes (mosses and liverworts) and vascular plants was the invention of cellulose in their cell walls, and cell plate formation at cell division; handy for resisting the effects of being in the air: gravity and wind.
Bryophytes, the mosses and liverworts are small plants, the two aquarium genera, Riccia and Ricciocarpus are about 1/2 an inch (2 centimeters) long, and most others are under 20 cm.. Due to a lack of waxy cuticle (as opposed to the "higher" vascular plants) they are mainly found in warm and moist environments. There are some 24,000 described species.
Bryophyta are divided into three classes, the mosses (Musci with 14,500 species), Anthocerotae (hornworts with about 100 species) and the group we're interested in, the liverworts, Class Hepaticae with the remaining 9,000. Regarding the common name "liverwort"; this is taken from a ninth century "Doctrine of Signatures" theory that the physical appearance of an object indicated special properties. In this case that some liver-shaped liverworts might be useful in treating ailments of the liver. The term "wort" simply means "herb" and therefore is a common plant suffix.
Ricciaand Ricciocarpus are amongst the simplest of liverworts; due to a lack of vascular, transporting tubules like the more advanced plants, they don't have actual leaves (instead called thalli, singular thallus, meaning "plant body"), branches or roots.
Riccia fluitans LINNAEUS, 1753;
Synonyms:Ricciella fluitans A. Braun; Riccia franconiae Lorbeer.
Natural Distribution & Ecology: Worldwide; An amphibious species; can be completely aquatic, terrestrial in moist settings, floating to rhizoid-anchored.
Physical Description:Masses of interlocking pale to dark green dichotomous "branches" that are thin (1/16") ribbon-shaped, linear to forked, forming interlocking ball-shaped colonies.
Riccia rhenana LORBEER from K. MULLER, 1941
Natural Distribution & Ecology: Worldwide; often found mixed in with R. fluitans. Under strong illumination separates, sinking to bottom; floats under dim lighting.
Physical Description:Similar to R. fluitans but tips of "leaves" are shorter and more pointed. Anchor themselves to substrate with single-cell rhizoids.
Ricciocarpus natans (Linnaeus) Corda
Synonyms:Riccia natans Linnaeus; Riccia capillata Schmidel; Riccia velutina Wilson; Ricciocarpus vetulinus Stephani.
Natural Distribution & Ecology: Worldwide. Amphibious; bisexual, with both sex organs occurring on same plant. Branching of thallose portions ("leaves") is dichotomous; much more pronounced in terrestrial forms.
Physical Description:Darkish green heart-shaped "leaves", 5-10 mm in width, with rounded edges. Purplish underneath with fine hairy rhizoids, root-like structures.
Ricciacan be grown free floating or "rooted". The single cell "roots" are actually anchoring rhizoids, that don't serve nutrient or water absorbing functions. Both genera propagate quickly and easily to form spongy, floating masses... often becoming a nuisance that needs to be periodically thinned to allow light penetration.
Substrate/Soil:Unimportant to these species as they derive nutrients directly from the water. Sand or gravel bottom.
Light/Lighting (intensity, spectrum, duration): Also of little consequence. These bryophytes adapt to a wide variety of light conditions. Grow more quickly with brighter lighting.
pH, KH, Other Chemical:Wide pH tolerance (6.0-8.0), moderate to hard water (5-20 KH).
Temperature Range:Broad range by species; 60-86 F. (15-30 C.).
Species Kept With:Most any they will not impugn by overshadowing. Do very well with Cryptocoryne and Vallisneria species.
Trimming:Excess material should be gingerly netted or siphoned out, as to not spread it, starting unwanted colonies. Should you end up with uncontrollable spread, adding salt at the rate of two or three teaspoons per gallon over a period of as many days (assuming your other livestock are tolerant) will kill these liverworts back. Take some stock out and set it aside in another container to reintroduce.
Pests & Predators:These plants are susceptible to overgrowth and smothering by pest algae, especially filamentous types. If you can't prevent these outbreaks through nutrient limitation, you'd do well to rip-out and discard the affected portions of your bryophyte colonies. Copper or other algicides are contraindicated.
The most or only really conspicuous generation of these plants is the gametophytes, the other, small, sporophyte generation is deeply embedded in the principal, gametophyte. Released when gametophytic generation dies, decays, liberating spores (generally as terrestrials).
Most folks start a new batch by simply breaking off a healthy section of an existing colony.
A note here that should be superfluous; take tremendous care in disposing unwanted bryophyte material. These plants easily adapt to aquatic and moist terrestrial conditions, and can create great havoc if introduced haphazardly.
Talk about "oldies but goodies". Riccia and Ricciocarpus have been part of the aquarium interest from the beginning; and for good reasons. They are hardy, functional plants that fare well under a wide range of conditions. In fact, their only downside is the same; they're just too prolific for their own good.
Should you happen upon these species, do keep some under absolute control in a large jar or dedicated tank; to replace the colonies in your main display systems that may spread out of control or get overgrown by algae.
Brunner, Gerhard. 1973. Aquarium Plants. T.F.H. Publications, NJ. 159 pp.
Riehl, Rudiger & Hans A. Baensch. 1982, 96 ed. Aquarium Atlas, v. 1. MERGUS, Germany. 992 pp.
Riehl, Rudiger & Hans A. Baensch. 1996. Aquarium Atlas, v. 3. MERGUS, Germany. 1104 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.
Ricciain aquarium use:
1) A floating function as egg catcher here with the red rainbowfish, Glossolepis incisus.
2,3) Two demersal shots of Riccia rhenana; Kent Webster's home rainbow tank utilizing metal halide lighting and CO2 infusion, and a store (Neptune's) example.