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 63<br />
tightly bound to hyphae) but such knowledge is sometimes <strong>of</strong> supplementary value, e.g. when<br />
comparing M. eximia versus M. nigella and M. olivacea versus M. tuberculata.<br />
A more important diagnostic character in Micarea is <strong>the</strong> colour <strong>of</strong> <strong>the</strong> hypo<strong>the</strong>cium in water<br />
mounts, and <strong>the</strong> corresponding colour changes obtained by <strong>the</strong> addition <strong>of</strong> KOH and HNO3. A<br />
discussion <strong>of</strong> <strong>the</strong> pigments involved is given under 'chemistry'.<br />
The height <strong>of</strong> <strong>the</strong> hypo<strong>the</strong>cium (in vertical section) is largely dependent on <strong>the</strong> overall size and<br />
(especially in species with a poorly developed excipulum) convexity <strong>of</strong> <strong>the</strong> apo<strong>the</strong>cium. The<br />
measurements given in <strong>the</strong> species descriptions relate to normally developed, non-tuberculate<br />
apo<strong>the</strong>cia. This character is <strong>of</strong>ten very variable for a given species and consequently <strong>of</strong> Uttle<br />
diagnostic value when comparing closely similar species. One exception to this is <strong>the</strong> case <strong>of</strong> M.<br />
contexta (20-90 /am) versus M. melaena (80-160 /xm).<br />
In Lugol's iodine <strong>the</strong> hypo<strong>the</strong>cial tissues are non-amyloid, although <strong>the</strong>re is sometimes a faint<br />
bluing in <strong>the</strong> vicinity <strong>of</strong> ascogeneous hyphae (especially in <strong>the</strong> upper part <strong>of</strong> <strong>the</strong> hypo<strong>the</strong>cium).<br />
Excipulum<br />
The size and distinctiveness <strong>of</strong> <strong>the</strong> excipulum ('ectal excipulum') in Micarea varies greatly<br />
according to species and <strong>the</strong> age <strong>of</strong> <strong>the</strong> apo<strong>the</strong>cium. In species such as M. cinerea, M. crassipes<br />
(Fig. 4B), A/, peliocarpa, and M. ternaria <strong>the</strong> excipulum is sufficiently well developed that <strong>the</strong>ir<br />
young apo<strong>the</strong>cia are <strong>of</strong>ten weakly or distinctly (M. crassipes) marginate in outward appearance.<br />
However, even when well developed and initially distinct, <strong>the</strong> excipulum may become reflexed<br />
and ± occluded as <strong>the</strong> apo<strong>the</strong>cium expands and increases in convexity (Fig. 3A-B) or becomes<br />
tuberculate (Fig. 3C). In many species <strong>the</strong> excipulum is always extremely reduced or absent<br />
(Fig.4A).<br />
When present, <strong>the</strong> excipulum is composed <strong>of</strong> outwardly radiating branched and anastomosing<br />
hyphae that ± separate in K. The hyphae closely resemble paraphyses, but are usually more<br />
dense and more richly branched. With markedly convex apo<strong>the</strong>cia it can be difficult to<br />
distinguish between reflexed portions <strong>of</strong> <strong>the</strong> hymenium and what might be an excipulum. In such<br />
cases <strong>the</strong> excipulum (if present) can be identified in good thin sections by <strong>the</strong> absence <strong>of</strong> asci and<br />
a negative (non-amyloid) reaction to Lugol's iodine. The excipulum <strong>of</strong>ten differs in colour or<br />
colour intensity from <strong>the</strong> hymenium, although a similar colour difference may sometimes be<br />
shown by reflexed parts <strong>of</strong> <strong>the</strong> hymenium.<br />
In M. crassipes and rare forms <strong>of</strong> M. lignaria ('f. gomphillaced') <strong>the</strong> excipular and hypo<strong>the</strong>cial<br />
tissues become vertically extended to form a stipe (Figs 3E, 4B).<br />
Anamorphs (conidial states)<br />
With a few noteworthy exceptions, such as Lindsay (1859, 1872) and Gliick (1899), <strong>the</strong> conidial<br />
states (anamorphs) <strong>of</strong> lichenized fungi have received little detailed attention from taxonomists.<br />
Several recent monographic studies have shown that anamorphs can provide useful characters at<br />
various hierarchial levels <strong>of</strong> classification and <strong>the</strong> reader is referred to Vobis (1980) and Vobis &<br />
Hawksworth (1981) for fur<strong>the</strong>r background information on <strong>the</strong> conidial states <strong>of</strong> lichens.<br />
Within <strong>the</strong> genus Micarea <strong>the</strong>re is a diverse array <strong>of</strong> anamorphic forms, possibly unrivalled by<br />
any o<strong>the</strong>r genus <strong>of</strong> lichens, except perhaps for some <strong>of</strong> <strong>the</strong> genera in <strong>the</strong> Asterothyriaceae<br />
(Vezda, 1979) . Information gained from <strong>the</strong> study <strong>of</strong> anamorphs has proved invaluable to me for<br />
<strong>the</strong> delimitation <strong>of</strong> species in Micarea; indeed, several species frequently occur without<br />
apo<strong>the</strong>cia but with numerous pycnidia, such that a detailed knowledge <strong>of</strong> <strong>the</strong> latter is <strong>of</strong>ten<br />
essential for <strong>the</strong>ir identification (see 'key to species without apo<strong>the</strong>cia').<br />
Conidiomata<br />
The conidiomata are usually pycnidial, and are globose, ovoid, doliiform, or ceriberiform in<br />
shape. They may be immersed (or partly so) within <strong>the</strong> thallus or substratum, sessile, or borne<br />
on stalks (pycnidiophores). When stalked, <strong>the</strong> pycnidia are usually ± doliiform and <strong>the</strong><br />
stalk-tissue is comprised <strong>of</strong> loosely interwoven hyphae bound by a gel matrix which is <strong>of</strong>ten<br />
pigmented. In addition, <strong>the</strong> 'stalk-part' <strong>of</strong>ten includes effete pycnidia (Fig. 35B-D). The stalks<br />
are sometimes branched due to <strong>the</strong> simultaneous development <strong>of</strong> two (or more) pycnidia at <strong>the</strong>