Identification notes
Gymnostomum calcareum is a specialist plant of sheltered moist friable calcareous habitats such as crumbling limestone rock ledges and blocks of tufa. The leaves are a bright green colour and are strap shaped with a bluntly acute apex. They are quite widely spreading, giving a starry appearance like a large version of Leptobarbula berica. This is a larger plant, however, that can form dense cushions, 1cm or so tall. Capsules are rare and lack a peristome.
Under the microscope the plane margins, long parallel sided leaves, densely papillose cells and a nerve almost reaching the apex are characteristic. A nerve section will show a strong band of abaxial stereids.
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