![]() Though much smaller in number than the Bryopsida, the Polytrichales are widespread. Within the class Polytrichopsida the members of the class Polytrichales generally have very robust gametophytes that are readily noticed. It's not surprising that most of the mosses people come across belong to the class Bryopsida. About 95% of all moss species belong to the class Bryopsida, whereas Takakiopsida contains only one genus, Takakia, with just two species. The classes in the 2000 classification vary greatly in size. ![]() Implicit in that debate are two different views about evolutionary history. The debate is about whether those two groups warrant separate divisions. Notice that everyone agrees that the "Takakia" and "Sphagnum" groups are markedly different from all other bryophytes. Those holding that view would then have two additional phyla, Takakiophyta and Sphagnophyta, with the phylum Bryophyta reduced from six to four classes. A number of bryologists maintain that the Takakiopsida and Sphagnopsida are so unlike any other mosses that those two classes should in fact constitute separate phyla. ![]() In the 2000 classification scheme the phylum Bryophyta is divided into six classes: Takakiopsida, Sphagnopsida, Andreaeopsida, Andreaeobryopsida, Polytrichopsida and Bryopsida. It provides a good framework on which to build a short account of the principles of moss classification and against which to contrast some findings from later studies. That classification is based on a mixture of molecular, morphological (macroscopic and microscopic) and cell structure data and, for the sake of brevity, will be referred to as the 2000 classification on this web page. The starting point is the moss classification scheme set out in the paper given in the next Reference button. Classification and identification Mosses (phylum Bryophyta)
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