Taxonomic revision of the genus Marchantia L. in Japan

概要

Asexual reproduction is a fundamental reproductive mechanism recognized in
bryophytes (Frey & Kürschner 2011). As one type of specialized asexual propagules,
gemmae show considerable morphological diversity in bryophytes (Cavers 1903; Imura
1994; Imura & Iwatsuki 1990). In some case, morphological differences in gemmae help
to identify species, even among closely related species (Bastos 2008; Borges 2006; Evans
1910; Iwatsuki & Deguchi 1981). In complex thalloid liverworts, many species belonging
to the genus Lunularia, Neohodgsonia and Marchantia produce multicellular gemmae in
cup-shaped structures called “gemma cups” (or “cupules”). In Marchantia, the gemmae
are multicellular discoid structures with two laterally placed apical notches. The central
part of the gemma is several cells thick and becomes gradually thinner toward the onecelled margin (Bischler-Causse 1989; Shimamura 2016). The germination of the thallus
from gemmae in Marchantia has been used as an experimental system in which to study
physiological responses of plants to various environmental factors and the gene functions
in morphogenesis (Bowman 2016; Eklund et al. 2018; Equihua 1987; Furuya et al. 2018;
Mirbel 1835; Naramoto et al. 2019; Shimamura et al. 2017; Solly et al. 2017; Suzuki et
al. 2020) and microbiome studies (Kobae et al. 2019; Nelson et al. 2018).
Since the establishment of the genus Marchantia (Linnaeus 1753), various attempts
have been made to define the taxa at the subgeneric, species and subspecies level based
on the morphological characters, such as number of ventral scales rows, morphology of
the appendage of the median ventral scales, gemma cup margins, spore ornamentation
and alternative patterns of archegoniophores lobes and involucres (Arnell 1963; Bischler
1984; Bischler-Causse 1989, 1993; Bischler-Causse et al. 2005; Burgeff 1943; Gradstein
& Costa 2003; Horikawa 1930; Lu & Huang 2017; Schuster 1992). However, no attention
has been paid to the morphological characters of gemmae as taxonomic traits. In general,
it is assumed that the morphology of gemmae is very uniform throughout the genus
Marchantia and it does not helpful to identify the species (Bischler-Causse 1989, 1993;
Evans 1917). Recently, Zheng & Shimamura (2019a) in a comparison of gemmae
morphology of M. polymorpha and M. pinnata have suggested that morphological
diversity of gemmae is worthy of re-consideration as a taxonomic character that has been
overlooked. ...

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