It stands knee- to waist-high, a dense, upright shrub of reddish-brown twigs. Its leaves are narrow, greyish-green, toothed near the tip, and dotted underneath with tiny golden glands that hold the scent. Before the leaves in spring it carries short, stiff catkins, reddish on some plants and yellowish on others. Brushing through a stand on a warm day releases a smell like pine and sweet hay together, strong enough to follow a walker for a few strides.

It grows where the ground is always wet and poor: the fen edges and reed margins of the Confluence Basins, above all the Reedmere, and the backwaters of the Lower Serath. It forms low, grey-green belts between reed and firmer ground.

It spreads by its roots into thickets and does well where little else will. Its roots fix the poorest wet ground and leave it better.

It is long-lived, coming back from its roots after cutting or burning, and flowers each spring before leafing.

Its chief use is against the biting gnats and whining flies of the warm wet months (see Marsh Insects). Reedfolk lay it under sleeping mats and in rafters, rub it on the skin, and burn a handful in the evening fire. Basin brewers who brew without hops use it to flavour and keep their ale, and a strong myrtle ale is said to give headaches. Its leaves keep fleas and moths out of bedding and clothes chests.

It harms no one in measure. Too much in ale is bitter and heady, and women with child are told to keep off it, which may be right.

Reedfolk say a house that smells of myrtle has been kept, and they leave a sprig on the threshold of a new stilt house. Some believe it keeps off more than gnats, the fevers of the low ground among them; it does keep off some of the insects that carry them, though nobody knows that is why. Basin folk say a myrtle ale makes a man brave and a fool in the same cup.