The Fossombroniineae comprise four genera of simple thalloid liverworts, namely, Fossombronia, Austrofossombronia, Petalophyllum and Sewardiella. A character presumed to unite the taxa of the suborder is the enclosure of the sporophyte in a calyptra which is in turn surrounded by a leaf-like pseudoperianth. Although many authors accept this interpretation of the shoot/sporophyte association, the developmental studies of Chalaud (1928. Rev. Gen. Bot. 41: 1-343, 8 Pl.) suggest that the structures produced in Fossombronia are not homologous to the pseudoperianths of the other taxa. Using serial paraffin sectioning and SEM techniques, we have investigated pseudoperianth formation and growth in several species of Fossombronia and Petalophyllum. In Petalophyllum a true pseudoperianth, formed from extensions of the lamellae, surrounds the cluster of unfertilized archegonia; following ferilization, the pseudoperianth expands and a shoot calyptra develops around the sporophyte. In contrast, Fossombronia first forms a perigynial mass beneath the fertilized egg. One or two leaf-like scales are subsequently produced at the apex of this perigynial mass at its point of juncture with the calyptra. This developmental sequence agrees with Chalaud's interpretation and verifies that the leaf-like structure that encloses the sporophyte in Fossombronia is not a pseudoperianth.

Key words: development, Fossombronia, perigynium, Petalophyllum, pseudoperianth