Bulletin of the British Museum (Natural History)

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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 .
62 BRIAN JOHN COPPINS Fig. 34 Two types of paraphyses in Micarea tuberculata. A, normal, non-pigmented paraphyses. B, stout, pigmented paraphyses. Scale = 10 /^m. distinct they have been referred to as the 'subhymenium' and 'hypothecium' respectively (e.g. Hertel, 19776). The term 'hypothecium' in this context has been substituted by many students of non-lichenised discomycetes by the term 'medullary excipulum' (Korf, 1973), and was called the 'ental excipulum' by Eckblad (1968). In Micarea the two layers are well-differentiated in only a few species (e.g. M. crassipes); and in the present work 'hypothecium' refers to all ascocarp tissue lying below the hymenium, apart from the excipulum (where present). This same terminology was adopted in the recent study of Catillaria by Kilias (1981). The hypothecium in Micarea is composed of deeply staining (e.g. in LCB and ammoniacal erythrosin), swollen-celled ascogenous hyphae (c. 2-5 /am wide) and moderately staining, slender 'structural' hyphae (c. 0-7-2 fxm wide; slightly varying in width according to species), embedded in a gelatinous matrix. In species with a colourless or pale hypothecium the matrix is ± dispersed in K and the hyphae are then clearly visible ( x 400) . In some species with a coloured hypothecium the pigment may be ± evenly distributed through the matrix and the hypthae are similarly distinct in K (e.g. M. eximia, M. olivacea, and M. turfosa). However, in the majority of species with a darkly coloured hypothecium (e.g. M. assimilata, M. botryoides, M. melaena, M. myriocarpa, M. nigella, M. sylvicola, and M. tuberculata) the pigment, although present in the matrix, exists as a strongly adhering coat around the hyphae, such that the hyphae appear thick-walled and broad (c. 1-5^ /xm). The pigment coatings tend to bind the hyphae together so that they are often indistinct in K. For the routine identification of Micarea species it is not essential to know the location of pigment (i . e . ± B H evenly distributed through the gel-matrix versus
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5. Micarea bauschiana (Korber) V. W
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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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