Marchantia quadrata is a species of liverwort, a simple non-flowering plant that grows as a flat, green, leaf-like structure (thallus) typically found on damp rocks and soil along stream banks in the Northern Hemisphere. The species was originally classified in its own genus Preissia due to its distinctive features, including larger spores and lack of the specialised cup-like reproductive structures common in other liverworts, but genetic studies have shown it belongs within the genus Marchantia. Like most liverworts, it reproduces both sexually, through separate male and female plants that produce umbrella-like reproductive structures, and through regeneration from fragments. The species prefers slightly drier habitats than its relatives and shows significant genetic variation across its range, suggesting it may comprise several distinct but closely related species.

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