The Yealm (pronounced "YALM"), also known as Thatch Reed or the Common Water Reed, grows in swamps, coastal wetlands, and marshes across Sarvonia. It provides shelter for waterbirds and insects, cleanses the water, and is commonly used by humans for roofing material.

Image description. The Yealm Reed, growing in swamps, coastal wetlands and marshes across Sarvonia. Picture drawn by Quellion.

Appearance. A tall beige stalk of spongy reed bears aloft a small hand-size plume, long strap-like beige leaves rising elegantly from the base of the stalk. The single plant can range from five fores to three peds, but is commonly found about two peds, or just over man-height. It invariably grows in large clumps or "beds", rising from the waters just off-shore. It prefers knee-deep water, salt or fresh, and a muddy rather than a sandy bottom.

The reed reproduces itself via its tuberous root, an elongated sponge that sends out sproutlets through the mud and then creates more tubers, from which the baby stalks grow each spring. The young green reeds are very flexible, slightly oval in cross-section, and porous; as they age they take on a beige colouration and water-repellent exterior, and eventually, if left to ‘dry’, a mithralene sheen which gives its stalk and plume a lovely delicate appearance, as if crafted from silver feathers. When dry, in the autumn it sheds a scattering of grains from its plume which float on the water and are quickly gobbled up by fish or waterbirds.

After the first frost, in colder areas, the reeds stiffen and snap easily, forming a tangle of tilted stalks and nests and burrows which waterbirds find irresistible. New growth shoots up through the tangle in the spring, and silt filters through, settling around the heavy roots. The mass of Yealm thickens and traps even more mud every year, until eventually the water’s edge is forced back and new shoreline is effectively created.

Territory. Since this plant will tolerate either salt or freshwater, it is quite prolific. The reed grows luxuriantly in the Fens of Yantha, the Seanian Swamps, and the Estuary at Brinsley. Parts of Wind Bay are almost choked with it. Small lakes throughout Sanguia and Enthronia are almost always fringed with Yealm Reed, one reason for its popularity as a roofing material in the region.

Usages. The grains, which do not seem to serve any reproductive purpose, feed the same water animals whose droppings nourish the plant. The root purifies the water around it (see below) and the stalks serve as shelter for many small waterbirds. The plant also protects tidal shorelines and can even replenish shorelines when occurring in bulk.

Apart from its beneficial role in the aquatic ecosystem, the plant has long been popular as a water-repellent, cheap, and effective thatch. Gathered into bundles, bound, combed, and twigged onto the sway-covered rafters of a small dwelling, Yealm Reed is both insulation and shingle for the less wealthy. Only a few tools are required, a pile of reeds, and a good supply of twigs or liggers with which to fasten the reed down.

Long, light timbers or saplings known as "sways" are nailed or lashed crosswise to the bare rafters. Then bunches of reeds, with their porous ends facing down, are "pinned" down with ligger twigs or lashed to the sways, starting from the bottom and working up in "courses" all around the roof. When the final course is laid, the ridge area goes on last. It is usually woven as a long separate panel on the ground and then staked into place atop the whole affair like a doily on a girl’s head. Different finishing designs are popular in different villages, and sometimes it happens that an entire small town can be seen from a distance as a series of grey patterns, like silver embroidery on a green field.

Research/Development. The tuberous roots are not only a reproductive system, they appear to be the plant’s main nutritive intake device. Water is sucked into the spongy mass and filtered, the nutrients and dissolved organic materials taken up into the stalk to nourish the Yealm Reed, and the purified water pumped back out. In effect, the plant can cleanse the water around it. Since in a fully-stocked ecosystem the animals and birds and decaying plant material are constantly replenishing the organic material (we shall not specify, for reasons of delicacy), this cycle can continue infinitely. However, it has been found that when the Yealm is planted in a closed environment such as a garden pond, where fish are not available to continue enriching the water, the reed’s efficiency is such that the water becomes completely pure (safe to drink!) and the pond rendered sterile as a result - unable to support life.

Mages and other researchers are currently experimenting with cultivating this reed downstream of large cities, in an attempt to deal with the inevitable slurry of sewage and dirty water which goes from high to low, causing objections from the "low". Some noticeable effects may already be seen in the mouth of the Mashdai River (near Marcogg) and the Wynein (Carmalad), and the Lower Quarters of Chylikis report that the Thaehelvil Stream can be used for washing clothing again. Evidently public education regarding the reed’s abilities will need to be introduced in these areas as well.