Bulletin of the British Museum (Natural History)

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LICHEN GENUS MICAREA IN EUROPE 21 similar habitats. During this study numerous specimens of Micarea have been found in folders of widely misinterpreted ('dustbin') names, such as ' Bacidia sphaeroides' , 'Catillaria erysiboides' and Lecidea vemails' . Copies of the list of specimens examined have been lodged at BM, DBN, E, GZU, M, NMW, UPS and US. Field studies Methods I have attempted to observe as many as possible of the accepted species in their natural habitats because such experience is invaluable for the appreciation of environmentally controlled variation and ecological requirements. For this end I have made field studies in most parts of mainland Britain, and also S.E. Ireland, Denmark (N. Jylland), mid- and N. Sweden. In addition, I have collected Micarea specimens during earlier expeditions to France (Bretagne) and western Ireland. I have been successful in finding two-thirds of the European species, and all but two {M. asslmllata and M. subleprosula) of the 31 British species. Light microscopy Observations and measurements of external features were mostly made at x50 using a Vickers stereomicroscope equipped with a measuring eyepiece. Internal features were investigated with a Wild M20 microscope which was fitted with a drawing tube and a 2-5 x adapter for the drawing of spores and conidia etc. Most sections were made by hand with a razor blade, but some were cut by a freezing microtome. Sections were usually mounted in water, followed by (or directly in) 10% or 50% KOH(K), domestic bleach(C), 50% HNO3, or ammoniacal erythrosin (0-5g erythrosin in 100 ml 10% ammonia solution), but other mountants such as cotton-blue in lactophenol (LCB), congo red, and alcian blue were also used at times. Tests for amyloid reactions were made by mounting directly in Lugol's iodine solution (Ig iodine and 2g potassium iodide in 300 ml distilled water), or in this solution following treatment with 10% KOH. More permanent preparations were made by ringing mounts in LCB with nail varnish, or by mounting in polyvinyl alcohol (PVA) or cotton blue in PVA (see Omar etal, 1979). For further details on techniques see also 'Guide to keys and identifications' (p. 100). Thin-layer chromatography The t.l.c. techniques employed were those described by Walker & James (1980) which are based on the standard method of Culberson (1972) . For the purposes of routine analysis only two of the three basic solvent systems were found to be necessary (i.e. H.E.F. and T.D.A.). Nomenclature In the list of synonyms for a given species each entry begins with the oldest valid name (basionym) and is followed with later combinations included in Hedlund (1892), Smith (1911, 1926), and James (1965^), and some others which have important nomenclatural implications. Zahlbruckner (1921-40) and Lamb (1963) should be consulted for additional combinations. The entries are listed chronologically, except for entirely invalid (or illegitimate) and misapplied names which are included at the end of the lists. Abbreviations of authors are according to Hawksworth (1980); those of journals to the third [1980] edition of Serial Publications In the British Museum (Natural History) Library; and those of books to Hawksworth (1974) or Stafleu & Cowan (1976-81). Apart from those newly described in recent years, few names in Micarea have been formally typified (according to Art. 7 of the Code); all cited lectotypes and neotypes are selected in this work, unless otherwise indicated. The nomenclature of lichens not treated in detail mainly follows Hawksworth et al. (1980) , but a few later changes are used. ,
22 BRIAN JOHN COPPINS Morphology Thallus Thallus structure in Micarea is crustose and basically simple, but nevertheless, encompasses much interspecific and intraspecific variation. For the purposes of explanation thallus morphology can be roughly divided into five types. [Note: the discussion of the first type includes some general features applicable to all types.] (i) Areolate-type (Fig. lA-C) The term areolae (pi.) is used here to describe discrete, rounded (when viewed from above), flattened, or more usually convex (sometimes ± globose) portions of the thallus which have developed directly from the prothallus lying in or on the substratum. These should be distinguished from the (often angular) segments derived from the cracking of a previously continuous crust. The areolae in Micarea mostly range from the 0-06 to 0.2 mm diam, but are characteristically larger in certain species. Thalli comprising smaller, discrete, granular, soredia- Uke structures (goniocysts) are dealt with in the next category (ii). Species that have well-developed, convex areolae sometimes appear ± squamulose, e.g. M. assimilata, M. incrassata, M. lignaria (as in type of Lecidea trisepta var. polytropoides) , M. melaenida, and M. subviolascens. Catillaria zsakii (a synonym of M. melaenida) was placed in the squamulose genus Toninia Massal. by Lettau, but its thallus is not truly squamulose and it was excluded from Toninia by Baumgartner (1979). In M. subviolascens (and to a lesser extent in some other species) the areolae become confluent and the resultant crust becomes secondarily cracked into 'islands' (each containing several primary areolae), thus giving the thallus a rather squamulose appearance. The areolae in most species are whitish or pale to medium grey, and often tinged dull greenish, bluish or brownish. The areolae of M. lignaria var. endoleuca are characterically ivory or cream-yellow. More vivid yellow, citrine or orange thallus colourations are not known in Micarea. A few whitish, arachnoid, prothalline hyphae are sometimes visible in specimens with scattered areolae, but a thick prothallus as found, for example, in some species of Phyllopsora (Swinscow & Krog, 1981) is unknown in Micarea. The thallus in most Micarea spp. is effuse and wide-spreading, and even when thalli form small patches amongst other lichens, a delimiting hypothallus, such as found in many species of Fuscidea and Lecidella, is never formed. Small thalU forming ± circular patches amongst other lichens, suggesting parasitic behaviour, are characteristic of M. intrusa{p. 140). In vertical section the areolae usually lack a well-defined cortex, but their surface is sometimes covered by a thin (c. 2-10 (xm thick), hyaline amorphous layer which does not dissolve in concentrated KOH (Fig. lA, C). Such a layer is found in the areolae of, e.g. M. alabastrites, M. assimilata, M. cinerea, M. elachista, M. incrassata, M. lignaria, M. peliocarpa, M. subnigrata, M. subviolascens, and M. ternaria. Areolae with a similar external appearance, but without an amorphous covering layer, can be seen in well-developed specimens of, for example, M. denigrata, M. nitschkeana, M. globulosella, and sometimes A/, melaena (Fig. IB). The thallus of these species (and to a lesser extent that of M. elachista) is often invaded and disrupted by the dematiaceous hyphae of a fungal parasite(s), and non-lichenized algae, resulting in a dark, often blackish, scurfy crust. This phenomen on is best exemplified by M. melaena, which in Britain is rarely found with a healthy, well-developed thallus. By contrast, during my excursions in Sweden I found it to be rarely parasitised. Susceptibility to invasion by parasites or opportunists may be related to climatic factors, being increased in the British Isles by the overall weather and warmer conditions. It would appear, therefore, that the amorphous covering layer (never present in M. melaena) is an effective barrier against potential invaders, but whether or not this is the reason for its evolution is a matter for speculation. The nearest approaches to the development of a true cortex are found in M. elachista and M. melaenida. Sections of healthy areolae show an outer layer (c. 10-12 /xm and 12-20 /xm thick respectively) of compacted, evacuated hyaline hyphae (Fig. IC). The amorphous covering layer of M. elachista often partially disintegrates causing the areolae to exhibit a white-pruinose appearance, a feature not noted in any other species of the genus.
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90 BRIAN JOHN COPPINS fM. elachista
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LICHEN GENUS MICAREA IN EUROPE 95 T
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Infrageneric considerations LICHEN
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5. Micarea bauschiana (Korber) V. W
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32. Micarea osloensis (Th. Fr.) Hed
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34. Micarea prasina Fr. LICHEN GENU
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conferanda (Lecidea) 205 confusula
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populina (Lecidea, Micarea) 31,32 p
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