Mosses.

Mosses and hornworts are included among the Bryophyta. They are older and more primitive than the vascular plants.

Java Moss (Vesicularia dubyana). Java Moss is the only moss widely employed in tropical aquaria. Old-time aquarists used to struggle with Fontinalis antipyretica, a similar-looking aquatic moss that hails from temperate-zone waters and can barely squeak by for a few months in an unheated tank that doesn't get much above 65^oF before it begins to disintegrate. Java Moss now has another rival, that's more of a contender: in the late 1990s a "Christmas Moss" with a densely-branched growth pattern began to be available, under Takashi Amano's general influence, especially through Singapore suppliers. There are some Aquatic-Plants Digest threads concerning this pretty new moss archived at theKrib.com, but no one seems very secure about its real identity.

Java Moss is native to southeast Asia--— not unexpectedly--— from Sumatra to the Philippines, and it's so undemanding it will even grow in slightly brackish water, or in tanks lit by scarcely more than one watt per gallon. Tangles of Java Moss will sometimes be enough to give fry a sporting chance of survival. A ten gallon tank loosely filled with skeins of Java Moss is the least stressful birthing tank for a livebearer. Moss helps delineate territories too.

The "vesicles" of Vesicularia are the "pearling" bubbles of oxygen it covers itself with in strong light. The bubbles may be enough to make an unattached mass of Java Moss buoyant, and lift it to the surface. Java Moss extends cinnamon-brown hairlike rhizoids with which it clings to surfaces, even ones as slick as the rear glass of my tanks.

Not everyone thinks Java Moss is an advantage. The loose growing style of Java Moss is just too messy for some tidy fishkeepers. Bits that break loose in the current will start new colonies wherever they fetch up. Strands will attach to gravel. They tend to wind round your filter's impeller, where you may have to pluck the threads off with tweezers, or stroke with a filterstem brush. So some techniques of controlling Java Moss could be as helpful as advice on how to grow it.

To clean Java Moss. Java Moss does tend to collect detritus, but unattached tangles can be taken out and dashed gently in a bowl of water. Or you can flush detritus out of Java Moss with the hose when you're adding new water, and let the filtration take it up. I used to ruthlessly snip or tease out bits that were algae-coated and throw them away, as part of my ongoing nitrate exporting regime. Now I may lay fouled strands of Java Moss in the blackworm tray instead. In a few days the worms will have picked it fresh and clean.

Discarded Java Moss can be used to mulch your house plants, where it mats down neatly and will keep its green color for many weeks, even dry. If you feel you need every shred of Java Moss you have, even the algae-ridden strands, I think you'll be disappointed by the Clorox dip for ridding plants of cyanobacteria and algae. Clorox is harder on mosses than on "higher" plants. But you can put algae-ridden Java Moss loosely into a jar of tapwater and stash it in complete darkness for about five days. The level of chlorine in tapwater will be hard on the epiphytes, and during the days of darkness, algae and cyanobacteria, which have no way to store reserves of nutrients, will give up the ghost. Rinse off the Java Moss daily while you do this. After the first day or so, you'll see the algal chlorophyll dyeing the water.

To remove Java Moss where it's infiltrating other plants. If you don't like the look of Java Moss among other plants, use a long-handled filter-stem brush, the kind with a cylinder of short bristles half an inch across, to snag unwanted Java Moss. Just twirl it gently onto the bristles, like winding spaghetti on a fork, and withdraw the wad from the tank.

Floating Java Moss. Java Moss can be made to hang down from a floating piece of natural cork bark like Spanish Moss. I take a small chunk of cork bark and tie a loop of monofilament round the middle. A strand of Java Moss can be gently rolled in a wet cloth til it makes a moderately tidy long loose wad. Then I tease one end through the loop of monofilament. I like this effect, which creates pools of shade and shafts of light that can be mysterious and beautiful. You can soften the corners of the tank this way, or disguise the riser of a sponge filter or the heater's cord. Hanging Java Moss makes a natural spawning mop if you want to retrieve some eggs from the danios, barbs, tetras etc. that are gamely spawning in your community aquarium. The surfaces of Java Moss provide extensive living space for more biofilm community; you'll often see fry or pencilfish picking their way among the strands and nibbling on the protozoans.

A moss lawn. Alternatively, Java Moss can be grown as a tight "lawn" covering a coconut shell. Prepare the coconut shell by covering it with boiling water and steeping it overnight to leach out some of the tannins. Now get a large enough glass bowl, under which the coconut shell can stand without touching the sides, and a glass plate for it to stand on. With a scissors, snip half-inch snippets of Java Moss and let them fall all over the coconut shell. Don't try to arrange them with your fingers or you'll go crazy. A light spritz from a mister will settle the sprigs flat against the coconut fibers. Pour half an inch of water into the bottom of the plate and cover it with the glass bowl. Then set this mini-terrarium that you've created into a brightly lit north window, where it doesn't get direct sun (which would cook it). In the bright humid atmosphere, the moss will revert to its denser, ground-hugging terrestrial style. If the contents look or smell a little moldy, I rinse the mold away and prop up the bowl with a wooden matchstick. If the moss gets to looking dry, I spritz it. In a very few weeks, when light green growing points show all over the moss, you'll know the moss has taken hold of the coconut fibers. Give it a gentle rinse to dislodge any snippets that didn't take, and put the greened-up coconut shell into your aquarium. You can pull it out again once every six weeks or so, to clip the "lawn" very close with the flat of the scissor blades.

You can do the same trick with a flower pot fragment that's going to be a spawning cave. A moss-coated flowerpot makes a less obtrusive object than the usual raw one. Um, but is the result a "Chia pot"? 

Java Moss will also take hold on a rock, if you bind it down with black thread wound several times round the rock. By the time the thread decomposes, the Java Moss will have taken hold. Nylon thread doesn't decompose the way cotton thread does. Everyone else seems to have more success with this than I do, but Java Moss certainly attaches itself to rocks and pebbles in the aquarium if I don't particularly want it to. Flat cobbles grown with Java Moss lawns are handsomer than trying to get it to grow directly on the substrate. And you can remove them one at a time, for a trim.

Java Moss grown on plastic netting can make a green curtain for the rear of the tank.

Hornwort (Ceratophyllum demersum.) Hornwort isn't part of my own plant repertory, because my water is so soft that Hornwort just fragments and dissolves within days. But that probably won't happen for you. In harder waters, Hornwort thrives, sucking up those nitrates and endlessly extending its growing tips, till it fills the surface of the aquarium. Hornwort naturally floats just below the surface of still waters. Aquarists often want to "root" it, It's not a plant that can make roots, being a cousin of the mosses and all. Instead, it will form some rhizoid holdfasts, and will quickly grow to the surface again. Instead keep discarding older sections, just retaining the fresh growth. That's how the nitrogen gets exported. It outcompetes algae, partly by competing for nutrients, but probably also by means of chemical warfare, the plant technique known as "allelopathy," which means something akin to "unkindness to strangers." Hornwort is brittle; rambunctious fishes may break it up. It's very sensitive to copper and medications in the water, which will make it shed all its feathery leaves. And it's a little sensitive to steamy temperatures; you'll grow better Hornwort in a cooler tank.