Taxonomy and distribution of Lejeunea exilis (Lejeuneaceae, Hepaticae)

Drepanolejeunea subacuta (Horik.) H.A. Mill. et al. and Lejeunea lancistipula (Steph.) H.A. Mill. et al., previously known only from Taiwan and New Guinea, respectively, are proposed as synonyms of Lejeunea exilis (Reinw. et al.) Grolle. Lejeunea exilis is a highly variable species and its diagnostic characteristics include (1) dimorphic under-leaves (bilobed and subulate-ovate), (2) very small size of plants, (3) eplicate perianths always strongly emergent, (4) highly variable shape of leaves, (5) acute to apiculate leaf apex of the leaf in well developed plants, and (6) asexual reproduction usually by means of ribbon-like marginal regenerants. Lejeunea exilis is reported for the first time for China. A detailed description and illustrations of Lejeunea exilis are provided. The occurrence of ribbon-like marginal regenerants in the Lejeuneaceae is discussed.