Ensure that leaf, rhizoid, tuber, bulbil and sporophyte characters are all assessed from the same plant. Because different Bryum species commonly grow closely intermixed it is only by demonstrating physical connections between say leaves, stems and tubers that one can be sure they are on the same plant.

Avoid basing records on very scanty material (e.g. single stem with few leaves, or plant with <5 tubers) or poor material (e.g. plants grown shaded or in water, as betrayed by weak, straggling growth with sparse leaves on long slender stems). Particular care to select good material is needed with difficult taxa such as B. radiculosum or B. bornholmense, but desperately stunted material of such typically larger species as B. capillare, B. torquescens or B. alpinum can mimic the species that are always of small stature.

Beware of Pohlia spp., some of which can be confused with some Bryum. Pohlia have leaves unbordered, ± toothed above, with lamina cells often narrower than in Bryum, a combination of characters found in Bryum only in the otherwise rather distinctive B. alpinum. In fertile material of Pohlia the long and very narrow perichaetial bracts are diagnostic. Other distinctions are that Pohlia have leaves with the costa not or only slightly excurrent, some taxa are paroicous, and although the endostome cilia are often long and well developed they are not appendiculate or nodulose.

Juvenile plants of Bryum normally lack tubers and they never have well grown sporophytes, but they may develop axillary bulbils in certain species. Growing material on indoors or a visit later in the season may offer the only hope of identifying immature plants.

Leaf characters are those of well grown upper leaves. The largest perichaetial bracts have similar characters. Avoid using new growth, basal leaves, innermost perichaetial bracts, perigonial bracts, leaves from juvenile stems or leaves from slender innovations. Rhizoid characters should be judged from a sample of several rhizoids. Papillae or roughness are most apparent on the largest rhizoids. Both small (translucent) and large (opaque) rhizoids should be checked in transmitted light of varying intensity when seeking mauve or violet coloration.

Separate terms are used here for (a) Tubers, (b) Axillary bulbils and (c) Axillary gemmae (which are filamentous, i.e. uniseriate). Note that older literature uses term 'gemmae' for tubers. Buds (e.g. in B. caespiticium) can be confused with axillary bulbils, but buds are not dehiscent and they are often more variable in size with leaf primordia beginning to grow into leaves.

Despite comments in some literature, interspecific hybrids fortunately seem to be rare.

Corrections, additions and other suggestions are most welcome.

The Draft Key to European species of Bryum with rhizoidal tubers is available to download as a document in Rich Text Format, which should be compatible with most word processing programs.

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