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Thysananthus patrickmuelleri K. Feldberg, Gradst., Schäf.-Verw., Mamontov sp. nov. Holotype. Geoscientific Collection of the University of Göttingen, Germany (GZG), GZG.BST.22086. Additional specimens examined. Patrick Müller Amber Collection (Zweibrücken, Germany) MEX 70, MEX 71. Etymology. The specific epithet honors the amber collector Patrick Müller who has generously supported our research by providing numerous amber fossils for study, including all known specimens of this species. Age and stratigraphic level. 15‒23 Ma, Langhian – Aquitanian (early to middle Miocene), Simojovel, Chiapas, Mexico. Diagnosis. Incubously foliated liverwort with a ventral merophyte at least five cells wide; flagelliform branches present on lower parts of the shoots; lateral leaves conduplicate-bilobed; dorsal lobe convex, asymmetrically oblong-ovate with a rounded to obtuse apex, median lobe cells mostly elongate with distinctly cordate trigones; ventral lobule Lejeunea - type, ovate-rectangular with one hooked apical tooth and a truncate apex; underleaves suborbicular to rounded quadrate to obovate with a rounded to emarginate, recurved apex and entire, mostly revolute margins. Description. Gametophyte fragments yellowish to dark reddish brown, 2.7–5.04 mm long, main shoots 0.52–1.16 mm wide with leaves (Figs 4 A – C, 5 A – C, 6 A – E). Branching irregular, Lejeunea - type, primary branches either similar to main shoot, or flagelliform and microphyllous (Figs 4 B, D, 6 C, D); main shoot-like branches 1.26–4.8 mm long, 0.41–1.4 mm wide with leaves; flagelliform branches 0.2–0.24 mm wide; one secondary microphyllous branch becoming main shoot-like on upper part. Stem dark reddish brown to blackish, 40–70 µm in diameter; cortical cells possibly thick-walled and elongated [mostly obscured by underleaves], ventral merophyte ca. 5 cells wide; stem on large branches 40–60 µm in diameter, on flagelliform branches ca. 30 µm in diameter. Lateral leaves incubous, densely imbricate, alternate, widely spreading to erect-spreading or ... |