The Entodontaceae, as defined by Brotherus in the second edition of Engler and Prantl's Die natürlichen Pflanzenfamilien, are heterogeneous both in terms of gametophytic and sporophytic characters. The family, therefore, presents a good group on which to test the hypothesis of gametophytic plasticity within a conservative, sporophytically defined line of evolution.

  Extensive observations using both light and scanning electron microscopes focused on detailed peristomial morphology. The data were scored and coded for use in a computer-assisted Similarity-Graph Clustering program and for preparation of a Wagner-Tree. In addition, an attempt was made to understand trends in diplolepideous peristomial evolution, with special emphasis on the hypnoid peristome. Evidence indicates that the peristome of the Entodontaceae is derived from the generalized type found in the Hypnaceae and related families.

  At least within the Entodontaceae, the hypothesis of sporophytic conservatism is valid. The family is interpreted as being derived from an African, hypnoid ancestor. The Entodontaceae are defined by leaves with a short, double costa and well-differentiated alar cells. The capsules are erect with a double peristome inserted well below the mouth. The exostome teeth consist of relatively broad, striate to papillose plates mostly joined along a straight center line; on the back surface the lamellae are non-projecting. The genera included in the Entodontaceae are Entodon, Mesonodon (= Campylodontium), Erythrodontium and Pylaisiobryum.

  Trachyphyllum is transferred to the Thuidiaceae; Entodontella is moved to the Plagiotheciaceae, Levierella to the Fabroniaceae, Pterigynandrum to the resurrected Pterigynandraceae, Rozea and Pseudoscleropodium to the Brachytheciaceae, Nanothecium, Orthothecium, Plagiotheciopsis and Bryosedgwickia to the Hypnaceae, and Pleurozium and Orontobryum to the Hylocomiaceae. The genera included in the Entodontaceae, and those excluded from the family, are described and illustrated.

  The variation of vegetative character-states in the type material of the Campylopus cavifolius complex of species has been studied. Certain characters as size of lamina cells and number of cell rows along the leaf base vary by more than 200 % on leaves of a single plant. In view of this broad amplitude of variation Campylopus subfimbriatus Thér. is considered synonymous with C. chrismarii (C. Müll.) Mitt. and C. subannotinus Thér. & P. d. Vard. with C. multicapsularis (C. Müll.) Schimp. in Par. C. suboblongus Herz., differentiated from C. chrismarii by smooth leaf tips only, is regarded as a variety of the latter species.

  The studies reported on here represent a summation of what I have learned about the complex of genera including Kurzia, Megalembidium, Psiloclada, Drucella, and Isolembidium. These genera belong to a complex in which transverse to succubous leaves are the norm (the monotypic genera Megalembidium and Drucella forming exceptions), the cuticle is often roughened, Microlepidozia branches occur (the monotypes Psiloclada and Drucella forming exceptions), and in which there is a marked tendency for oil-body loss, partial or total. Most members are further characterized by a tendency towards formation of thick-walled, rigid, and relatively small cells. Members of the Kurzia-Psiloclada pair are closely allied to each other; Megalembidium is much less closely affiliated and, indeed, its relationships remain obscure. Equally isolated and, indeed, unique are Drucella and Isolembidium. Our understanding of this complex remains very imperfect; I had once hoped to produce a monograph of the entire group and the mass of data here presented has accumulated over 17 years (from 1962 to 1979) Investigations of branching patterns, stem and sporophyte anatomy, reported on fully here, may eventually point the way to a clear understanding of the whole complex. At this point, however, monographic treatment is impossible; any such attempt, today, would only result in a pseudomonograph. However, I have made a very detailed study of the taxa present in two areas: Australasia and North America. For these areas I can include a treatment of almost all the taxa.

  Field work forming the background of these studies was pursued in North America (1942-1979), Japan (1974), New Zealand (1961-62, 1967), New Guinea (1967), Tasmania (1962), South America (1961, 1969-70, 1976, 1979), Europe (1978 and earlier), Fiji (1962, 1967), Tahiti (1967) and elsewhere. Long residence, in New Zealand especially, permitted detailed investigation of critical taxa through use of masses of fertile material and allowed investigations of oil-body presence or absence, dispersal and form. As a consequence, I have been able to investigate in some detail 30 taxa at the species and infraspecific level; keys to these taxa are also included. Of the 33 species listed by Grolle for Kurzia (1964), all but a handful have been studied. All species of the other genera have been studied and are herein illustrated.