Bulletin of the British Museum (Natural History)

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LICHEN GENUS MICAREA IN EUROPE 83 Fig. 52 A-B, M. ternaria, mesoconidia; A, (H-NYL 18682 - holotype); B, {Thomson 9188, DUKE). C, M. aff. ternaria (Fair Isle, 1976, Duncan, BM), mesoconidia. Scale = 10 fjun. B
84 BRIAN JOHN COPPINS In the case of M. denigrata it is a general rule (but with exceptions) that when on worked wood (fence-posts, garden furniture, window frames, etc.) its thallus has numerous pycnidia (with mesoconidia) and often few (if any) mature apothecia. On natural substrata (e.g. fallen tree trunks in old woodlands) pycnidia with microconidia or macroconidia are more prevalent, although they are usually relatively fewer in number and associated with numerous apothecia. It seems highly likely that the success of M. denigrata as a primary coloniser of newly available substrata is largely due to the successful role of its mesoconidia as asexual propagules. Its microconidia probably function as spermatia, but the function of the macroconidia is less obvious, although I suspect that they, like the mesoconidia, act as asexual diaspores (perhaps in a different way). Another observation pertinent to this discussion is that I have frequently observed the mesoand macroconidia of Micarea species being extruded through the ostioles of the pycnidia as white mucilaginous blobs; such phenomena are usually seen after periods of wet weather. It is tempting to suggest that these extrusions facilitate dispersal beyond the limits of the parent thallus by the action of rain or passing arthropods and mollusca. Dispersal by invertebrates may be of especial importance for species such as M. botryoides, which occur in sheltered situations rarely subjected to rain-wash. I have only rarely observed microconidia being extruded as white blobs, thus suggesting that there is no need for them to be dispersed beyond the limits of the parent thallus. Indeed, if microconidia do function as spermatia, and if the mycobiont of the Micarea is homothallic, there would be no requirement for them to be dispersed more than a few millimetres. Conidiogenous cells The conidiogenous cells of Micarea species are always phialidic, although in many cases the phialides are seen to undergo 'percurrent proliferation' (Figs 42B, 44B). The conidiogenous cells belong to Types I or II of Vobis & Hawksworth (1981) and arise from the inner wall of the pycnidium (or on the outer surface of the sporodochium in M. adnata). Their subtending cells are never sufficiently regular in shape for them to be termed 'conidiophores'. In several species whose pycnidial walls are intensely pigmented the bases of the conidiogenous cells are often similarly pigmented (Figs 47B, 51B). The nearest approach to the differentiation of wall-tissue from a conidiogenous layer is found in the thick-walled pycnidia of M. elachista. There is much variety in the shape of conidigenous cells (e.g. ampuUiform, doliiform, lageniform, cyUndrical) and there is sometimes much variation within a single pycnidium (Figs 42B, 44A). Conidiogenous cells with long cyhndrical necks often have swollen bases (Figs 38A, 47B, 5 IB). Although critical observations and measurements have not been made for all species, the size and shape of conidiogenous cells have rarely been found to be useful characters for the separation of closely similar species. However, one exceptional case is that of saxicolous forms of M. olivacea (Fig. 47A) versus M. tuberculata (Fig. 5 IB), in which the conidiogenous cells of the latter are much longer. Chemistry The discussions below are presented under two sub-headings. The first deals with 'lichen substances', which are readily extractable in acetone and identifiable by thin-layer chromatography (t.l.c; see 'Methods'). The second part deals with pigments that cannot be analysed in this way; their chemical nature is at present unknown and they can only be characterised by their colour in water and subsequent reactions with reagents such as K and HNO3. Lichen substances Prior to the present studies there is little evidence in the literature to suggest that species of Micarea contain any lichen substances. However, there are a few hints given in some early descriptions: for example, Leighton (1879: 362) gives 'K+ yellow, C+ orange-red' reactions for Lecidea milliaria [Micarea lignaria], which probably relate to his specimens of the var. endoleuca. The only reported t.l.c. analysis of a Micarea appears to be that of Huneck &
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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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30 BRIAN JOHN COPPINS Fig. 5 Sketch
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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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