Sphagnum is a kind of moss — a soft, low, green plant with no flowers — that grows in cold wet ground. Its special quality is that it holds water like a sponge; a handful can hold many times its own weight. Because of that, gardeners buy it dried and mix it into soil, or wrap it around plant roots, and it is sold in Taiwan for orchids and other pot plants. It is usually uncountable: some sphagnum, a bag of sphagnum. You will most often see it as part of a longer name — sphagnum moss (which is really saying moss twice, but everyone says it) or sphagnum peat moss. Over hundreds of years, dead sphagnum presses down into peat, the brown material people once cut and burned for fuel, so the word also appears in writing about bogs and about the climate, because those wet places hold a great deal of carbon. Two more things I like to mention: sphagnum is slightly acid and keeps things from rotting, which is why bodies thousands of years old have been found whole in these bogs; and in the First World War, when there were not enough bandages, people cleaned and used sphagnum on wounds. It is a scientific-sounding word, and outside gardening and science most English speakers would just say moss.

水苔、泥炭蘚（園藝店賣的「水苔」，種蘭花常用）