The familial placement of Jubula has long been controversial be- cause of this genus' possession of both frullanioid and lejeuneioid features. As- sessment of significance of these traits, however, has not involved a comparative developmental study of all taxa in the genus. In this study, experimental and histological techniques have been used to study morphogenesis and anatomy of representative taxa. Throughout the genus, sporelings develop precociously and possess both endosporic and exosporic protonemal phases, much like Ceratolejeu- nea, while growth and differentiation of the adult plant is Frullania-like. Leaf brace cells are lacking, water-sac development and insertion are as in Frullania, and branches are of either the Frullania or the Bryopteris types. Antheridia generally occur on Bryopteris-type branches, which are spicate in most taxa to capitate in Java populations; production of male inflorescences on Frullania-type branches characterizes Hawaiian populations and experimental Jubula pennsylvanica. Archegonia occur in pairs or, rarely, in groups of 3 at the apex of the main shoot and possess long, slightly twisted necks. Following fertilization they will be en- closed by an elongate, 3-keeled perianth, and a single set of bracts and bracteoles, and will be subtended by one or two Radula-type innovations. The sporophyte generation of all taxa possesses a small, turnip-shaped foot, a reduced seta and a globose capsule. Although smaller than most Frullania sporophytes, this spo- rophyte possesses a frullanioid developmental pattern. The morphogenetic pat- terns of all representative taxa and populations are extremely constant and suggest that Jubula has been derived from Frullania and is phylogenetically distinct from the Lejeuneaceae.