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Bulletin of the British Museum (Natural History)

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LICHEN GENUS MICAREA IN EUROPE 177<br />

Map 19 Micarea prasina substance A # 1950 onwards O Before 1950<br />

white) thallus, but equivalent morphological forms containing 'unknown A' are sometimes<br />

encountered. Specimens containing 'unknown C are exceedingly rare and are known only from<br />

coastal turf in south-west England and <strong>the</strong> Channel Islands, and on argillaceous soil on a bank by<br />

a woodland path in south-eastern Schleswig-Holstein. The above ecological and phytogeographical<br />

tendencies require to be more thoroughly tested throughout <strong>the</strong> range <strong>of</strong> M. prasina,<br />

and it is possible that a good case for <strong>the</strong> taxonomic recognition <strong>of</strong> <strong>the</strong>se races as varieties,<br />

subspecies, or even species could be made.<br />

The type material <strong>of</strong> Lecidea subviridescens contains 'unknown C and has spores that are at<br />

<strong>the</strong> high end <strong>of</strong> <strong>the</strong> overall size range for M. prasina s. ampl. (10-18x4-5-5 /xm) and some with<br />

two or three septa. However <strong>the</strong> very large 2-3-septate spores are always old with secondarily<br />

thickened walls, and similar spores are sometimes encountered in o<strong>the</strong>r Micarea species that<br />

have predominantly 1-septate spores. Fur<strong>the</strong>rmore, similarly large, 2-3-septate spores have<br />

been found in some coastal specimens containing 'unknown A' and in some inland, lignicolous<br />

specimens containing 'unknown B'. Although I regarded 'subviridescens'' as a separate species in<br />

<strong>the</strong> recent <strong>British</strong> checklist (Hawksworth etal., 1980: 62), I now believe it should be subsumed<br />

under M. prasina pending fur<strong>the</strong>r studies as intimated in <strong>the</strong> preceding paragraph.<br />

Habitat and distribution (see also 'observations'): As an epiphyte on trees or shrubs M.<br />

prasina has been found on a wide range <strong>of</strong> phorophytes; in Britain <strong>the</strong>se include Acer, Alnus,<br />

Betula, Castanea, Corylus, Fagus, Fraxinus, Metrosideros, Quercus, Salix, Sambucus, Sorbus,<br />

Ulmus, Calluna, Erica, Rhododendron, Vaccinium, Sarothamnus, Ulex, Abies, Larix, Picea^<br />

Pinus, Pseudotsuga, and Juniperus. It occurs on <strong>the</strong> bark or lignum (old dried wounds, etc.) <strong>of</strong>

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