Ecology

Bryophytes are found on every continent, including Antarctica, and represent an impressive diversity of over 17,000 species. They are especially diverse and abundant in moist areas, such as the coastal rainforest of the Pacific Northwest, but many can also grow in very dry conditions. Some bryophyte species are extremely tolerant of desiccation, and can survive for months or even years without water.

Bryophytes are an important part of many ecosystems, especially those of the temperate rainforests. They play a role in nutrient uptake and turnover, soil stabilization, and site colonization, and they provide food and shelter for many other organisms. Since they do not have roots, bryophytes can live even in areas where there is no soil. They use rhizoids to anchor themselves onto rocks and trees, and they absorb water and nutrients through their leaves. Over time, the accumulation of dead and decaying mosses on top of rock forms a layer of soil that other plants can then colonize.

Evolution

Bryophytes were once considered to be all part of the same division (Bryophyta), but are now separated into three different groups with distinct evolutionary histories (Figure 1).

Figure 1. Phylogenetic tree depicting the relationships of the bryophytes (mosses, liverworts and hornworts) to the vascular plants and green algae.

The mosses (Bryophyta) are further divided into three classes: Bryopsida, which are know as the “true mosses” and make up 95% of mosses worldwide, Andreaeopsida, known as “lantern mosses,” which grow only on rock surfaces, and Sphagnopsida, commonly known as “peat mosses,” which often grow in bogs.

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