Bulletin of the British Museum (Natural History)

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LICHEN GENUS MICAREA IN EUROPE 31 This difference can be due to the much branched and entangled apices of the paraphyses, or (and) deposits of pigment in the gel-matrix, or on (or in) the walls of the paraphyses. The upper layer of the hymenium differentiated in such ways is perhaps more correctly termed the 'epihymenium' (Poelt, 1974a) or 'pseudoepithecium' (Korf, 1973). In its strict (original) sense an 'epithecium' refers to a layer of branches of paraphyses that overtop the asci. Such a layer is approached in some species of Micarea and is best exemplified by M. contexta and M. melanobola. In Micarea the difference between an 'epihymenium' and an 'epithecium' is not clear-cut, and so I have chosen to employ the latter term which has been long and widely employed in lichenology. The height of the hymenium in Micarea species is sometimes difficult to measure accurately because the hymenium often merges rather imperceptibly into the hypothecium. Measurements are most accurately made by mounting thin sections in Lugol's iodine, in which the strongly amyloid (dark blue) hymenium contrasts strongly with the non-amyloid (or ± so) hypothecium. Even when accurately determined the height of the hymenium is rarely a useful character in distinguishing similar species. The overall range in height is about 23-90 /am, and in most cases is within 35-50 /xm. Shallow hymenia (rarely exceeding 35 /am) are characteristic of many of the species with small spores, viz.: M. hedlundii, M. melanobola, M. misella, M. myriocarpa, M. nigella, M. olivacea, M. osloensis, M. rhabdogena, and M. tuberculata. Likewise, tall hymenia are characteristic of species with large spores, and the tallest hymenium (65-90 /u,m) belongs to the species with the largest spores, namely M. subleprosula. The height of the hymenium sometimes increases with the age of the apothecium, and this is particularly true in M. bauschiana and M. sylvicola: small, yet mature, apothecia usually have a hymenium c. 40 /zm tall, but as the apothecium enlarges and increases in convexity, the hymenium often increases in height up to about 60 /xm; at the same time the paraphyses appear to 'stretch' and become thinner (especially in the lower part of the hymenium). The hymenium in Micarea never contains hyaline, crystalline inclusions that adhere to paraphyses (as found in some species of Lecidella, and many Graphidaceae) or numerous oil droplets (as found in several species of Buellia and Caloplaca). Epithecial granules that dissolve in K and often give the apothecia a pruinose appearance are also never found in Micarea. Minute granules of blue-violet (K+aeruginose) pigment, like those found in Lecidea hypnorum, are occasionally observed in the hymenium of M. contexta and M. lignaria. The colour of the hymenium and epithecium is an important character in the identification of Micarea species. A discussion of the various pigments involved is given in the sections on 'chemistry'. The hymenium may be dilutely and ± evenly coloured throughout, or the colouration may be more intense in the upper part. In many species the hymenium is often intersected by dark vertical streaks, a feature usually due to dense pigment surrounding individual, or small fascicles of stout paraphyses (see p. 61). Asci The asci of Micarea species are clavate or cylindrical-clavate in shape and belong to the Lecanora-type of Honegger (1978). When mounted in Lugol's iodine (following treatment in 10% KOH) the ascus is seen to have a non-amyloid wall surrounded by an amyloid outer-layer ('fuzzy coat') and an internal staining amyloid apical dome (Fig. 6). Micarea has sometimes been placed in the Arthoniaceae (e.g. Lamb, 1953) but the ascus of members of that family does not have an amyloid outer-layer and the apical dome is not deeply amyloid. In a few species of Arthonia and Arthothelium I have observed a faint bluing in the part of the apical dome immediately adjacent to the ocular chamber. In some Arthonia species a tiny amyloid ring is apparent above the apex of the ocular chamber, and, despite statements to the contrary by Eriksson (1981), such a ring is found in the asci of ^. radiata (type species oi Arthonia Ach.) and A. fuscopurpurea. The same type of ring was also described for Bryostigma leucodontis by Poelt & Dobbeler (1979). Such aspects of ascus structure in the Arthoniaceae clearly merit more detailed investigation. The ascus structure in Micarea supports my opinion that the genus should be placed in the Lecideaceaes. str., at least for the time being. The asci of all European Micarea species are 8-spored. The North American Lecidea populina
32 BRIAN JOHN COPPINS Fig. 6 Ascus apex of Micarea alabastrites in optical section (LM); mounted in Lugol's iodine following pre-treatment in 10% KOH. A, young ascus. B, mature ascus. ac, apical cushion; aw, ascus wall; d, apical dome (tholus); oc, ocular chamber; ol, outer layer of ascus wall. Shading indicates intensity of amyloid reaction; note that in reality the apical cushion and ocular chamber are probably completely non-amyloid. Scale = 10 /xm. Miill. Arg. has 16-spored asci and was transferred to Micarea by Anderson & Carmer (1974). Unfortunately the type material of L. populina has been out on loan from H and not available to me during the course of this study. However, the species apparently occurs in Xanthorion communities and, if this is so, then it is unUkely to be a Micarea. Spores The wide variety of spore types found in Micarea can be seen in the selection of spores from all the European species illustrated in Figs 7-33. A few species (e.g. M. assimilata, M. contexta, and M. lithinella) have spores that are ± consistent in size, shape, and septation, but for many other species (e.g. M. anterior, M. botryoides, M. denigrata, M. prasina, and M. turfosa) these characters can be very variable even within the same ascus. The smallest spores are found in M. myriocarpa (5-5-8-5xl-5-2-5 jxm) and the largest ones are found in M. subleprosula (40-60X 5-6-6 /Ltm). Spores may be simple or up to 7-septate, the variations within these hmits depending on the species. Spores with more than 7-septa are very rare, although a few 9-septate spores have been observed in M. subleprosula, and a collection (Coppins, 1834) of M. synotheoides has spores with up to 11 septa. Among the great range of spore shapes encountered, some may be broadly ellipsoid {M. subnigrata and M. intrusa) , but regularly globose spores do not occur in Micarea. Healthy spores are always thin-walled and colourless. However, the walls of old spores trapped within the hymenium sometimes become slightly thickened and pale straw coloured, or they may become impregnated with hymenial pigment. Spore walls always appear smooth (LM at X 1000) and are never surrounded by a gelatinous epispore. The cytoplasm of spores, asci, and ascogenous hyphae in M. intrusa is sometimes a dilute orange, turning purple-red in K.
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LICHEN GENUS MICAREA IN EUROPE 95 T
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LICHEN GENUS MICAREA IN EUROPE 97 a
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Infrageneric considerations LICHEN
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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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