Further insight into lobule teeth homology in Lejeuneaceae subf. Lejeuneoideae from Cheilolejeunea oscilla, a new species from Australia

Abstract

Within the Lejeuneaceae the lobule papilla has been conceived to occupy three positions: proximal, distal, or ental of the apical tooth. This concept rests on the presupposition that the apical tooth in all species is homologous, an assumption that has been questioned but not demonstrably falsified. This paper describes a situation where characters describing the position of marginal papillae fail the test of conjunction, an explicitly testable criterion of homology, by co-occurring within an individual. This situation is presented by Cheilolejeunea oscilla, a new species from Queensland Australia. Variation in lobule morphology within individuals of C. oscilla demonstrates that a change from proximal to distal lobule papilla is achieved without altering the topological relationships between the first and second lobule teeth, and the lobule papilla. Therefore, the marginal papilla occupies the same position, proximal of the first lobule tooth, in all species of Lejeuneaceae subf. Lejeuneoideae, and apical teeth within typical Cheilolejeunea and Lejeunea are not homologous. The apparent difference in papilla position is due to the second lobule tooth being elaborated, and the first lobule tooth being incorporated into the lobule margin in typical Cheilolejeunea. One defining morphological character of Cheilolejeunea may be the presence of an elaborated second tooth, and on this basis the new combination Cheilolejeunea norrisii is proposed for a Tasmanian species previously referred to Lejeunea. The views of Mizutani and He, that referring to ‘apical’ teeth is ambiguous and the terminology ‘distal’ or ‘proximal’ when applied to lobule papilla position is positively misleading, are upheld. The need for descriptions of characters to accurately encapsulate the homology hypotheses they represent is stressed, and the need for greater attention to homology assessment when liverwort taxonomists propose characters and character states to describe their plants is again reiterated.