The Systematic Position of Adelothecium Mitt. and the Familial Classification of the Hookeriales (Musci)

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Abstract
On the basis of its intricately pinnately branched rhizoids, dark-red, opaque stems, strong single costa, and long axillary hairs Adelothecium is aligned with the unicostate genera of the Hookeriales. Within the group the genus appears isolated because of the presence of pseudoparaphyllia, the more or less unfurrowed exostome teeth, the production of gemmae on reduced axillary branches, and the insertion of the rhizoids well below the leaves or around the periphery of buds. An evaluation of gametophytic and sporophytic features within the Hookeriales indicates that two groups, distinct at family level, are present: The Daltoniaceae (consisting of the genera Achrophyllum, Adelothecium, Bryobrothera, Calyptrochaeta, Crosbya, Cyathophorum, Cyathophorella, Daltonia, Distichophyllidium, Distichophyllu, Leskeodon, and Leskeodontopsis), and the Hookeriaceae (consisting of Actinodontium, Amblyotropis, Brymela, Callicostellopsis, Crossomitrium, Cyclodictyon, Diploneuron, Helicoblepharum, Hemiragis, Hookeria, Hookeriopsis, Hypnella, Lepidopilidium, Lepidopilum, Leucomium, Phulophyllu, Pilotrichidium, Rhynchostegiopsis, Sauloma, Schimperobryum, Schizomitrium, Stenodesmus, Stenodictyon, Tetrastichium and Thamniopsis). The Cyathophoraceae, Distichophyllaceae and Adelotheciaceae are considered synonymous with the Daltoniaceae, while the Leucomiaceae is placed in the synonymy of the Hookeriaceae. The presence of a central duct in the stem of Dendrocyathophorum indicates that it should be placed in the Hypopterygiaceae.