Bulletin of the British Museum (Natural History)

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