Studies on type material of Marchantia fallax Herz. (Marchantiaceae)

Section Papillatae Bischl. is one of the most taxonomically complicated sections in the family Marchantiaceae, due to its ambiguous interand intra-specific delimitation (Zheng and Shimamura 2022). In East Asia, for many years only two subspecies, Marchantia emarginata subsp. tosana (Steph.) Bischl. and M. papillata subsp. grossibarba (Steph.) Bischl., have been recognised in this section (Bischler 1989; Bischler-Causse 1989; Zheng and Shimamura 2020). Although this treatment has been widely adopted in almost all Asian studies, the delimitation between the two subspecies remains ambiguous due to the overlap in some morphological characters, such as the blackish median band on the dorsal surface of the thallus, appendage of the ventral median scales, number of female receptacle lobes, and angle of the basal sinus of the male receptacle. In 2022, Zheng and Shimamura first noted the presence of these ambiguities in the two subspecies of sect. Papillatae in Japan and therefore partly clarified their delimitation by reducing Marchantia tosana Steph. (≡ M. emarginata subsp. tosana) and M. tosayamensis Steph. (= M. emarginata subsp. tosana) under M. papillata subsp. grossibarba. Marchantia emarginata subsp. cuneiloba (Steph.) T.X.Zheng & M.Shimamura was subsequently proposed to replace the former M. emarginata subsp. tosana. Because of the lack of available ordinary specimens from a wide geographical range, previously synonymised taxa of M. emarginata subsp. tosana were also tentatively transferred to subsp. cuneiloba. To provide a clearer delimitation of the two subspecies of sect. Papillatae in East Asia, and to lay the foundation for a future comprehensive revision of the section, these synonyms need to be reviewed. During the taxonomic revision of the family Marchantiaceae in Asia, it has been possible to study the original material of one little known Chinese species, Marchantia fallax Herz. This species was originally described based on a specimen from Yunnan Province, China (Herzog 1930). Since then, no further information on this species was published until Bischler (1989) synonymised the species under M. emarginata subsp. tosana without providing any comments. Detailed taxonomic notes were provided in a subsequent monograph (Bischler-Causse 1989); however, this synonymy still needs to be reviewed because when this treatment was produced, the morphological concepts of accepted species in sect. Papillatae, such as M. emarginata and M. papillata, were neither well understood nor clearly defined. In this note, a detailed description of Marchantia fallax, illustrations of its important taxonomic features, and taxonomic notes are provided.