Bulletin of the British Museum (Natural History)

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LICHEN GENUS MICAREA IN EUROPE 129 forms), sometimes emergent, hyaline grey or black; walls hyaline but usually dilute olivaceous or brownish, and K+ violet in the upper (exposed) parts; in endoxylic forms, walls olivaceous (K+ violet) throughout; of three types: (a) 60-150 ^im diam, ostioles eventually gaping; conidia (macroconidia) , curved or hamate, (l-)3-septate, 12-24xc. 1 /xm; (b) 80-160 ^im diam, ostioles often gaping: conidia (mesoconidia) short cylindric or obovate, sometimes faintly biguttulate, 2-8^-5(-5)xl-2-l-8 fxm often extruding from the ostioles as a conspicuous white blobs; (c) 30-50 /xm, ostioles not gaping; conidia (microconidia) narrowly fusiform or bacilliform, (4-5)5-7-5x0-7-0-8/xm. Chemistry: Thallus K— , PD— ; sections of thallus and apothecia C+ orange-red, rarely C— (also, parts with dull olivaceous pigment, C+ violet). If thallus is heavily parasitised and scurfy the C+ orange-red reaction may be difficult to obtain and gyrophoric acid may not be detectable by t. I.e. Observations: Micarea denigrata is a common and extremely polymorphic species exhibiting a wide range of genotypic and phenotypic variation. Its thallus can vary from being completely endoxylic to forming a thick, granular-verrucose, areolate crust. The colour of the apothecia varies from pallid, through grey or brown, to black in a ± direct relationship with exposure to Ught. Specimens may be abundantly fertile with numerous, large, mature apothecia. On the other hand, they may be ± sterile with just a few, scattered immature apothecia (or even none at all) but with numerous pycnidia containing mesoconidia; alternatively the latter may be replaced by pycnidia containing microconidia and, or, macroconidia. Indeed, all possible combinations of anamorphic states have been found and a few collections (e.g. Coppins 1888 and 8384) have all three states, plus apothecia, on the same thallus. Spore length is usually in the range of 9-14 /^tm, but extreme forms are known in which the range is 8-10 /x,m, or 12-18 ^m. Gyrophoric acid is usually present in the thallus and/or the apothecia (and easily demonstrated by tests with C), but in some specimens its concentration is low and only detectable with certainty by t.l.c. ; in a few diminutive, endoxyhc forms I have been unable to detect gyrophoric either by a C test, or by t.l.c. In short, M. denigrata exhibits extreme variation. Despite this, with care and patience the species is rarely difficult to separate from other, similar species. The biggest problems I have experienced are where the decision has to be made between what could be a diminutive form of M. denigrata with small spores, or a form oiM. misella with an unusually high proportion of 1 -septate spores and without its characteristic stalked pycnidia (that contain mesoconidia). Such decisions are settled by the careful observation and measurement of paraphyses, and microconidia (see couplet 11 of the main key and Table 7). Shade forms of M. denigrata with brown, ± globose apothecia have been confused with M. elachista, but the latter has a brown (K+ dissolving) epithecial pigment, a more complex thallus structure (with a 'cortex' and amorphous covering layer), distinctive pycnidia, and always lacks gyrophoric acid (sections of thallus and apothecia C— ). Forms of M. denigrata with a scurfy-granular thallus can be similar to M. prasina, but microscopic examination will show the thallus appearance to be caused by its disruption by invading foreign fungi and algae, and not by the presence of the small ± discrete granules (goniocysts) characteristic of M. prasina. Furthermore, M. prasina never gives C+ orange-red (gyrophoric acid) reactions, and it usually has broader, rarely curved spores with more rounded apices. The closest relative to M. denigrata is M. nitschkeana, which is ± identical with regard to thallus structure, pycnidial types, apothecia structure, pigmentation, and chemistry. Morphologically the only important difference is that the mature spores of M. nitschkeana are 3-septate and more consistently curved (cf. Figs 13 and 24B). In addition, the two species differ in their preferance of substrata: M. denigrata favouring lignum or dead bark of old tree trunks or stumps, and M. nitschkeana favouring corticate twigs and small branches of trees and shrubs. However, there is some degree of overlap as M. nitschkeana is occasionally found on the lignum of fence posts, but, on the other hand, I have never encountered M. denigrata on attached living, corticate twigs. In the field, well developed specimens of M. denigrata sometimes have a superficial resemblance to M. cinerea, M. lignaria, and M. peliocarpa, but these three species have K— hymenia and larger, 3 (or more)-septate spores. Diminutive endoxyhc forms of M. denigrata are indistinguishable in the field from the several,
130 BRIAN JOHN COPPINS predominantly lignicolous species with small, black apothecia, but all such species (except M. misella as discussed above) appear very different when examined microscopically. Habitat and distribution: M. denigrata is commonly found on the lignum of fallen trunks and old stumps of broad-leaved and coniferous trees, especially in rather open situations at the edges of woodlands, woodland glades, and hedgerows, etc. The communities in which it occurs are difficult to define, but to give some indication the following list of associated species has been made from collections from fallen decorticate trunks of Pinus in the native pine-woods of Scotland: Buellia griseovirens, Cladonia coniocraea, C. macilenta, Hypogymnia physodes, Lecanora expallens, L. symmicta agg., Lecidea aeruginosa, L. icmalea, Micarea peliocarpa, Mycoblastus sterilis, Parmelia saxatilis, Platismatia glauca, Pseudevernia furfuracea, Xylographa abietina, and X. vitiligo. M. denigrata is a very successful primary coloniser of untreated timber-work. It also occurs on the same substrate whose preservative has lost its effectiveness, or whose painted surface has flaked off. On such substrata M. denigrata has been found in a wide range of situations, e.g. gates, fence posts and rails, garden furniture, picnic tables and seats, window frames of greenhouses, wooden roof tiles (shingles), telegraph poles, and the woodwork of old carts and farm machinery. When on such worked wood it often forms almost pure stands, and is often present as a form with few apothecia but numerous pycnidia containing mesoconidia; the conidia often extruding as white blobs easily visible to the unaided eye or through a x 10 lens. Lichens associated with M. denigrata on worked wood in the British Isles include Buellia punctata, Cyphelium inquinans, Hypogymnia physodes, H. tubulosa, Lecanora conizaeoides, L. Map 7 Micarea denigrata # 1950 onwards O Before 1950
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. 18 BRIAN JOHN COPPINS 11. M.denig
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20 BRIAN JOHN COPPINS Micarea The g
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22 BRIAN JOHN COPPINS Morphology Th
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24 BRIAN JOHN COPPINS (ii) Goniocys
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26 BRIAN JOHN COPPINS A B Fig. 2 'M
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28 BRIAN JOHN COPPINS 3 00
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30 BRIAN JOHN COPPINS Fig. 5 Sketch
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32 BRIAN JOHN COPPINS Fig. 6 Ascus
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34 BRIAN JOHN COPPINS Fig. 8 M. ala
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36 BRIAN JOHN COPPINS Fig. 10 A, M.
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38 BRIAN JOHN COPPINS Fig. 12 A,M.
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40 BRIAN JOHN COPPINS r\ U Fig. 14
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42 BRIAN JOHN COPPINS Fig. 16 M. in
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44 BRIAN JOHN COPPINS Fig. 18 M. le
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46 BRIAN JOHN COPPINS Fig. 20 A-B,
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48 BRIAN JOHN COPPINS Fig. 22 M. me
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50 BRIAN JOHN COPPINS Fig. 24 A, M.
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52 BRIAN JOHN COPPINS Fig. 26 M. pr
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54 BRIAN JOHN COPPINS VJ Fig. 28 A,
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56 BRIAN JOHN COPPINS Fig. 30 M. su
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58 BRIAN JOHN COPPINS Fig. 31 - con
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60 BRIAN JOHN COPPINS Fig. 33 M. tu
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62 BRIAN JOHN COPPINS Fig. 34 Two t
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64 BRIAN JOHN COPPINS Table 1 Conid
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66 BRIAN JOHN COPPINS Fig. 36 Sugge
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68 BRIAN JOHN COPPINS Fig. 37 M. ad
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70 BRIAN JOHN COPPINS s o o c o c o
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72 BRIAN JOHN COPPINS n 1/ [\ f] n
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74 BRIAN JOHN COPPINS Fig. 43 A-B,
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76 BRIAN JOHN COPPINS Fig. 45 M. li
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LICHEN GENUS MICAREA IN EUROPE 179
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conferanda (Lecidea) 205 confusula
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populina (Lecidea, Micarea) 31,32 p
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