What are 2 major groups of mosses?

Answer 1

Higher-level classification of the mosses is still not fully settled, and there is still considerable difference of opinion on the names of the major groups. The cladogram below shows the relationships of the four major groups: Sphagnopsida (peat mosses), Andreaeopsida (lantern mosses), Polytrichopsida (nematodontous mosses), and the Bryopsida (arthrodontous mosses), which includes the diplolepidious and haplolepidious groups.

http://www.ucmp.berkeley.edu/plants/bryophyta/bryophyta.html


For more information about mosses, try the resources listing at the ABLS website. The American Bryological and Lichenological Society is devoted to the scientific study of all aspects of bryophyte biology.

You may also be interested in the Bryological Resources at the Missouri Botanical Garden, including a literature database, index of moss names, and bryological glossary.

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Mosses were traditionally grouped with the liverworts and hornworts in the Division Bryophyta (bryophytes), within which the mosses made up the class Musci. This group, however, is paraphyletic and now tends to be split up. In such system, the Division Bryophyta refers specifically to mosses. They appear to be the closest living relatives of the vascular plants.

The mosses are grouped as a single class, now named Bryopsida, and divided into seven subclasses:

Andreaeidae
Sphagnidae
Tetraphidae
Polytrichidae
Buxbaumiidae
Bryidae
Archidiidae


Andreaeidae are distinguished by the biseriate (two rows of cells) rhizoids, multiseriate (many rows of cells) protonema, and sporangium that splits along longitudinal lines. Most mosses have capsules that open at the top.

The Sphagnidae, the peat-mosses, comprise the single genus Sphagnum. These large mosses form extensive acidic bogs in peat swamps. The leaves of Sphagnum have large dead cells alternating with living photosynthetic cells. The dead cells help to store water. Aside from this character, the unique branching, thallose (flat and expanded) protonema, and explosively rupturing sporangium place it apart from other mosses.

The Tetraphidae are unique (as their name implies) in having only four large peristome teeth surrounding the opening of the capsule.

Polytrichidae have leaves with lamellae, which are flaps on the leaves that look like the fins on a heat sink. These help it retain moisture. They differ from other mosses in other details of their development and anatomy too, and can also become larger than most other mosses, with e.g. Polytrichum commune forming cushions up to 40 cm high.

The Buxbaumiidae are called 'bug mosses' because they usually have a very small and reduced gametophore and the whole plant is mostly the sporophyte capsule. The shape reminds one of a bug, which is the reason for its common name.

The Bryidae are the most diverse group; over 95% of moss species belong to this subclass.

The Archidiidae are distinguished by their extremely large spores and the way the sporangium develops.