Gymnomitrion Corda, Naturalientausch 12: 651, 1829.

Bakalin, Vadim, Choi, Seung Se & Park, Seung Jin, 2021, Revision of Gymnomitriaceae (Marchantiophyta) in the Korean Peninsula, PhytoKeys 176, pp. 77-110 : 77

Gymnomitrion Corda, Naturalientausch 12: 651, 1829.

Description.

Plants worm-shaped to ribbon-like, with densely imbricate leaves or similar to Marsupella and with loosely spreading leaves, rigid to soft, whitish to brownish, brown, rusty, and blackish brown, without red or purple pigmentation. There are two kinds of phenotypes: Gymnomitrion in the old sense and the former genus Apomarsupella R.M. Schust. nested within Gymnomitrion (cf. Shaw et al. 2015). The first phenotype, with imbricate leaves and stems creeping to ascending, subclavate, from rhizomatous base, dorsiventrally compressed, commonly immersed to the substrate and incrusted by soil particles. The second phenotype comprises plants with spreading leaves with shoots dorsiventrally not compressed, as well as having a not evident rhizomatous base. In both ‘phenotypes’ rhizoids are common in the rhizomatous shoot base and geotropic stolons, but rare in leafy parts of the shoot, soft, colorless to grayish or rarely and solitarily deep purple. Stem not evidently different in strata, rather it is monomorphic (outer layer cells slightly larger), cells with unequally thickened walls, and well-developed trigones. Leaves lobed to unlobed or shallowly emarginate, with plane or narrowly recurved margin. Leaf cells pachydermous, commonly with the rim of discolored cells. Dioicous (taxa known in Korea). Androecia intercalary, (1-)2(-3)-androus, stalk biseriate. Perigynium and perianth virtually absent or strongly reduced. Elaters bispiral.

Comment.

This treatment follows the recent emendations e.g. transfer to Gymnomitrion of the taxa Marsupella commutata (Limpr.) Bernet and Apomarsupella revoluta (cf. Shaw et al. 2015). These transfers made Marsupella more monomorphic in the series of features, but resulted in greater polymorphism in vegetative characters of Gymnomitrion , which now includes many taxa of ‘marsupelloid’ habit, although in reproductive characters is characterized by an absence, or strong reduction of, perianth and perigynium.