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 61<br />
Paraphyses<br />
The paraphyses in Micarea are characteristically thin and branched. When measured (in 10%<br />
KOH, or ammoniacal erythrosin) at <strong>the</strong> mid-hymenium <strong>the</strong>y may be very thin and only about<br />
0-6-1 fxm wide (e.g. M. anterior, M. botryoides, M. contexta, M. eximia, M. lithinella, M.<br />
misella, and M. prasina), or thin and c. 1-1-5 /xm wide (e.g. M. adnata, M. cinerea, M. denigrata,<br />
M. intrusa, M. muhrii, and M. peliocarpa), or relatively stout and about 1-5-1-8 fjun wide (e.g.<br />
M. assimilata, M. incrassata, M. lignaria, M. osloensis, and M. subnigrata) ; <strong>the</strong>se measurements<br />
relate to paraphyses not coated in pigment. In old, much expanded, apo<strong>the</strong>cia <strong>the</strong> paraphyses<br />
sometimes appear 'stretched' and thinner than normal (especially in <strong>the</strong> lower half <strong>of</strong> <strong>the</strong><br />
hymenium) ; this phenomenon has frequently been observed in collections <strong>of</strong> M. bauschiana, M.<br />
sylvicola, and M. lignaria. In many species <strong>the</strong> paraphyses gradually widen towards <strong>the</strong>ir apices,<br />
but <strong>the</strong> apices are never regularly clavate or capitate. This widening is <strong>of</strong>ten enhanced by <strong>the</strong><br />
deposition <strong>of</strong> closely adhering pigment which sometimes gives <strong>the</strong> appearance <strong>of</strong> a 'hood' (e.g.<br />
M. melaena) ; such coatings or hoods can be detached by gently boiling and <strong>the</strong>n tapping sections<br />
or squash preparations in 50% KOH. In a few cases (e.g. M. melanobola) <strong>the</strong> pigment cannot be<br />
separated in this way and appears to be located within <strong>the</strong> walls <strong>of</strong> <strong>the</strong> paraphyses. Paraphyses<br />
with dark pigmented apical 'caps', like those found in Catillaria s. str. (Killias, 1980: 253),<br />
Buellia, and many species <strong>of</strong> Lecanora, are not known in Micarea.<br />
In all species <strong>of</strong> Micarea a large proportion <strong>of</strong> <strong>the</strong> paraphyses are branched, even if <strong>the</strong><br />
branching is mainly confined to <strong>the</strong> epi<strong>the</strong>cium. Species with sparingly branched paraphyses<br />
include M. assimilata, M. incrassata and M. lignaria. Anastomozing paraphyses have been<br />
observed in all <strong>the</strong> species, but <strong>of</strong>ten <strong>the</strong> anastomoses are ± confined to <strong>the</strong> lower third <strong>of</strong> <strong>the</strong><br />
hymenium. The degree <strong>of</strong> branching and anastomosing is difficult to quantify for <strong>the</strong> practical<br />
purposes <strong>of</strong> identification, but this character can be useful when comparing collections micro-<br />
scopically.<br />
A similarly difficult character is <strong>the</strong> relative abundance <strong>of</strong> <strong>the</strong> paraphyses. The two extremes<br />
can be referred to as: (a) 'numerous' - large in number and immediately discernible when<br />
observing a mount in 10% KOH at x400; (b) 'scanty' - few in number and not immediately<br />
obvious when observed in <strong>the</strong> same way. In hymenia with scanty paraphyses <strong>the</strong> 'extra space' is<br />
taken up by hymenial gel or a higher proportion <strong>of</strong> asci, or a combination <strong>of</strong> both. The situation<br />
in most species lies somewhere between <strong>the</strong> two extremes. Fur<strong>the</strong>rmore, <strong>the</strong> relative propor-<br />
tions <strong>of</strong> hymenial gel and asci to paraphyses sometimes increases as <strong>the</strong> apo<strong>the</strong>cium expands (cf<br />
<strong>the</strong> above example <strong>of</strong> M. bauschiana, M. sylvicola, and M. lignaria). An accurate assessment <strong>of</strong><br />
<strong>the</strong> abundance <strong>of</strong> paraphyses is not usually essential for <strong>the</strong> routine identification <strong>of</strong> Micarea<br />
species, although it can be helpful when comparing difficult, convergent forms <strong>of</strong> M. denigrata<br />
and M. misella (see couplet 11 <strong>of</strong> <strong>the</strong> main key).<br />
In addition to <strong>the</strong> 'normal' paraphyses described above, <strong>the</strong> hymenium <strong>of</strong> several species (e.g.<br />
M. bauschiana, M. botryoides, M. eximia, M. nigella, M. sylvicola, andM. tuberculata) contain<br />
scattered individuals, or small fascicles, <strong>of</strong> ra<strong>the</strong>r stout paraphyses. These 'paraphyses' are<br />
about 2-3 /xm wide and usually more distinctly septate than normal paraphyses. Fur<strong>the</strong>rmore<br />
(especially in species with a dark hypo<strong>the</strong>cium), <strong>the</strong>y are <strong>of</strong>ten coated in pigment throughout<br />
<strong>the</strong>ir length (Fig. 34), with <strong>the</strong> result that <strong>the</strong> hymenium is seen to be intersected by dark vertical<br />
streaks. They are mainly found in species with 'scanty' paraphyses, and appear to extend deep<br />
into <strong>the</strong> hypo<strong>the</strong>cium. The elucidation <strong>of</strong> <strong>the</strong>ir true status and function awaits detailed<br />
ontogenetic studies, but it is possible that <strong>the</strong>y have a streng<strong>the</strong>ning, spacing or protective<br />
function during <strong>the</strong> maturation <strong>of</strong> <strong>the</strong> hymenium from <strong>the</strong> primary corpus.<br />
Hypo<strong>the</strong>cium<br />
The area <strong>of</strong> tissue lying below <strong>the</strong> hymenium, or between <strong>the</strong> hymenium and <strong>the</strong> excipulum (if<br />
present), is generally referred to by lichenologists as <strong>the</strong> 'hypo<strong>the</strong>cium'. In many groups <strong>of</strong><br />
lichenized discomycetes (including <strong>the</strong> Lecideaceae) this area can be divided into an upper,<br />
usually narrow, layer containing mainly ascogenous hyphae, and a lower, <strong>of</strong>ten much deeper<br />
layer <strong>of</strong> structural tissue (hyphae gelatinised to various extents, according to genus or species).<br />
These two layers are <strong>of</strong>ten <strong>of</strong> different colour or colour intensity. Where <strong>the</strong> two layers are<br />
.