The classification of mosses: Two-hundred years after Hedwig
Vitt, Dale H.
Classification of organisms results in a one dimensional ordering of taxa. The ordering is made more complex by interpolating ranks that denote affinities of the taxa. Thus, our modern nomenclatural system is hierarchical in nature and is able to provide a listing of ranked taxa that each in turn denotes affinities of the included taxa. The earliest moss classifications ordered taxa from simplest to complex, and placed taxa together based on a few selected features. As a result, many early classifications began with erect, unbranched mosses and ended with prostrate, highly branched taxa. Fissidens was often conceived to be the most simple because it is an unbranched moss with leaves on only two sides of the stem. Other early classifications arranged mosses that have capsules without an operculum (and thus do not open to disperse spores) first in the classification and those with dehiscent capsules last.