Featured below is a photomicrograph of the antheridial head from a genus of mosses known as Mnium. Mosses are simple, rootless plants that flourish in moist and shaded terrestrial habitats. They can be found worldwide clinging to soil, rocks and trees, in locations as biodiverse as the rainforests of the Amazon to coastal Antarctica.

Like other members of the Bryophyte family, mosses require water (even in the form of heavy dew) to assist in reproduction. Water facilitates transport of sperm from the male antheridium to the female archegonium, where the sperm fertilizes an egg to produce a zygote.

From zygotes, elongated structures begin to grow out of the clumps of moss. Upon reaching maximum length, the tips of these long stalks, called seta, begin to enlarge to form capsules, or sporangia. The sporangium, a spore-bearing region, contains minute, developing spores and is attached to the seta by a structure called a foot. Inside the capsule, spores develop to maturity by meiosis and are shed by wind currents and breezes.

Close examination of the capsule reveals a protective cover called the operculum, which falls away upon maturity. In order to ensure their release into a moisture-friendly environment, mature spores must pass by humidity-sensitive peristomal structures known as teeth; the teeth increase and decrease the opening at the end of the capsule by swelling and contracting in accordance with the moisture content in the air.

Mosses benefit their ecosystems by breaking down exposed soil, thereby releasing nutrients for the use of complex plants. Additionally, these low-lying evergreen plants deter the damaging effects of soil erosion by providing surface cover and absorption of water in moist terrestrial environments.