Beschreibung: A revision is made of the genera Hypnodendron and Braithwaitea. Mniodendron and Sciadocladus are reduced to Hypnodendron, Limbella is excluded from the Hypnodendraceae, and Dendro-Hypnum is considered to be not validly published. Hypnodendron rigidum Mitt. is transferred to Pterobryella. The species of Hypnodendron are grouped into nine sections. Five of these are monotypic, viz. Leiocarpos Dix. and four new ones: Lindbergiodendron (including H. arcuatum), Tristichophyllum (H. diversifolium), Mniodendropsis (H. milnei), and Pseudomniodendron (H. fusco-mucronatum). The circumscription of the family also needs revision, but has been maintained unchanged for the time being in the absence of information regarding assumedly related families.\nA number of morphological and other characters are discussed. Hypnodendron is thought to be of pleurocarpous descent; Meusel\xe2\x80\x99s derivation of the growth-form of Hypnodendron from that of the acrocarpous genera Mnium and Philonotis is rejected. Rejuvenation takes place by means of basal innovations, and in a number of erect species also by distal ones. The umbellate and palmate fronds are assumed to have been derived from a pinnate type. The Hypnodendraceae are distributed in the Indo-Pacific and Australasian regions and in southern South America. Hypnodendron is centred in Melanesia and New Zealand. 26 species are recognized, 9 of which are divided into subspecies or varieties; 5 taxa are reinstated (H. colensoi, H. comatum, H. comosum var. sieberi, H. spininervium ssp. spininervium and ssp. archeri) and 1 is described as new (H. vitiense ssp. australe). Identification keys are provided, and for each taxon are given: synonymy together with pertinent literature and typification, misinterpretations and misidentifications, description, geographical distribution, ecology, and notes on various subjects. Each species is illustrated, and a list is given of specimens examined, mostly accompanied by a distribution map.