Bulletin of the British Museum (Natural History)
Bulletin of the British Museum (Natural History)
Bulletin of the British Museum (Natural History)
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LICHEN GENUS MICAREA IN EUROPE 65<br />
Fig. 35 Micarea botryoides, conidiomata: diagram showing <strong>the</strong> various means <strong>of</strong> 'stalk' formation and<br />
branching (see text for fur<strong>the</strong>r details). Scale = 100 /xm.<br />
The pycnidia <strong>of</strong> species which consistently lack pigment in <strong>the</strong>ir apo<strong>the</strong>cia (e.g. M. adnata, M.<br />
alabastrites, M. pycnidiophora, and M. stipitata) correspondingly lack pigment in <strong>the</strong>ir wall<br />
tissues. In species with coloured apo<strong>the</strong>cia <strong>the</strong> pycnidial walls are usually (at least in part)<br />
coloured also. For a given species <strong>the</strong> pigment involved is usually that found in <strong>the</strong> hymenium (or<br />
epi<strong>the</strong>cium) <strong>of</strong> <strong>the</strong> apo<strong>the</strong>cia, but in a few cases (e.g. M. lutulata) it is <strong>the</strong> pigment found in <strong>the</strong><br />
hypo<strong>the</strong>cium which is involved. The link between apo<strong>the</strong>cial and pycnidial pigmentation helps<br />
distinguish pycnidia belonging to a Micarea from any intermixed pycnidia belonging to a<br />
non-lichenized or parasitic fungus. It fur<strong>the</strong>r helps to distinguish <strong>the</strong> pycnidia belonging to <strong>the</strong><br />
different species <strong>of</strong> Micarea in mixed populations; for example, <strong>the</strong> stalked pycnidia <strong>of</strong> M.<br />
misella (walls oUvaceous, K+ violet) are <strong>of</strong>ten found intermixed with those <strong>of</strong> o<strong>the</strong>r species such<br />
as M. anterior (walls reddish brown, K— ) and M. melaeniza (walls dark olivaceous, K-).<br />
When a pycnidium is deeply immersed in <strong>the</strong> thallus it is <strong>of</strong>ten only <strong>the</strong> uppermost part around<br />
<strong>the</strong> ostiole which is coloured, and likewise, if <strong>the</strong> pycnidium is semi-immersed it is <strong>of</strong>ten only <strong>the</strong><br />
upper, exposed part which is coloured. With <strong>the</strong> exception <strong>of</strong> <strong>the</strong> species that are characteristically<br />
devoid <strong>of</strong> pigment and some forms <strong>of</strong> o<strong>the</strong>r species in deep shade, <strong>the</strong> walls <strong>of</strong> sessile or<br />
stalked pycnidia are coloured more or less throughout.<br />
As mentioned above, <strong>the</strong> conidiomata <strong>of</strong> Micarea species are pycnidial, but <strong>the</strong>re is one<br />
exception to this. M. adnata has two anamorphic states: one in which <strong>the</strong> conidia (mesoconidia)<br />
are produced internally in immersed pycnidia; and ano<strong>the</strong>r where <strong>the</strong> conidia (macroconidia)<br />
are borne externally on cushion-like sporodochia which resemble small apo<strong>the</strong>cia. This latter<br />
state could be considered to be a hyphomycetous anamorph but comparative ontogenetic<br />
studies are required to investigate <strong>the</strong> <strong>the</strong>oretical possibility that <strong>the</strong>se sporodochia have<br />
evolved from pycnidial conidiomata by an exertion <strong>of</strong> <strong>the</strong> 'hymenium', and a thickening <strong>of</strong> <strong>the</strong><br />
subtending wall-tissue to form a supporting cushion (Fig. 36). Unfortunately this hypo<strong>the</strong>sis is<br />
not supported by intermediate forms in o<strong>the</strong>r species, although <strong>the</strong> pycnidia (with filiform or<br />
curved-hamate macroconidia) <strong>of</strong>, for example, M. cinerea and M. peliocarpa <strong>of</strong>ten have widely