INTRODUCTION TO MOSS IDENTIFICATION
4. The Three Bryophyte Divisions

Although older works considered them as separate orders within one big division (plant divisions are the highest levels of classification, equivalent to animal phyla), a more modern viewpoint is to acknowledge how different they are from one another and recognise the three types of bryophytes as comprising their own separate divisions. The word "bryophytes" might still be used in an informal broad sense to mean mosses and liverworts and hornworts, or in a more narrow sense, just mosses. Bryology is the study of all three and most bryologists have some degree of facility with the non-moss bryophytes as well (but most will agree that liverworts are a bit more challenging).

I. Hornworts (Division Anthoceratophyta) are uncommon and there are just a few species in OH, but one of them grows in open disturbed places where it can be abundant. The one shown here was captured along a newly cleared pipeline right-of-way in early October in Hocking County. Gametophytically, a hornwort is dorsiventrally flattened, sprawling and  irregularly shaped, suggestive of a thallose liverwort. The sporophytes are indeed horn-like, and split lenthwise starting from the top to release spores as they mature.

Liverworts (Division Marchantiophyta) are fairly common, but they are rarely abundant or large enough to be noticed easily. (A notable exception is Bazzania trilobata, which occurs in large patches on the ground in hemlock dominated forests). Liverworts often occur sparsely mixed in with mosses. They are quite variable. The most well known types from biology class, the tongue-shaped flattened thallose liverworts, such as Marchantia, are actually much  less common than the more moss-like leafy liverworts. Compared to mosses, the leafy liverworts tend more often to be flatter with their main leaves in two ranks or rows and reduced underleaves. Also, the leaves are sometimes much more elaborate than moss leaves, being variously lobed or dissected. The leafy liverwort sporophyte is very delicate and short-lived.
 

Mosses (Division Bryophyta) are the most abundant, speciose, and conspicuous bryophytes. Most often, their leaves are in whorls about the stem (although many are somewhat flattened). The leaves are never (in our species) lobed or divided, and the sporophytes, when present, tend to persist on the plants and are useful in identification. 

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