Bulletin of the British Museum (Natural History)

LICHEN GENUS MICAREA IN EUROPE 19
eluded from the genus and the new combinations, Psilolechia clavulifera (Nyl.) and Bacidia prasinata
(Tuck.), are proposed. Keys for the identification of all the accepted European taxa are given. The taxonomic
parts are preceded by an outline of the historical background to the study of Micarea, and details of
materials and methods employed in this study. Detailed accounts of the morphology, chemistry, and
ecology in the genus are provided , and a discussion of distributions is supported by maps for the British taxa.
All Micarea species occur on acidic, nutrient poor substrata, and most are confined to cool-temperate,
boreal, or oceanic regions; a few occur in arctic-alpine areas but the genus is poorly represented in
dry, lowland, Mediterranean regions. Prior to this study, most of the species were little-known or
misunderstood; clarification of their taxonomy has been achieved by paying particular attention to their
anamorphic states, chemistry (including pigmentation), and detailed anatomy. Consideration of the
distribution and ecology of the species has proved invaluable in ordering the taxonomic chaos which previously
surrounded the notoriously variable species of the genus.
Lecideaceae
Historical background
Until recently the circumscription of the Lecideaceae (and of the genera within it) had changed
httle from that adopted by Zahlbruckner (1926). It included most Uchens with the following
combination of characters: a crustose to squamulose thallus, a 'grass-green' phycobiont
(excluding Trentepohlia and Phycopeltis) , ± immersed to sessile, disc-like apothecia without a
thalhne margin, mainly colourless spores, and an absence of parietin (or related pigments) and
(or) polarilocular spores. The principal genera in the family (e.g. Lecidea, Catillaria, Bacidia,
Biatorella, Mycoblastus, Lopadium, Bombyliospora, and Toninia) were separated mainly on
the basis of spore characters, i.e. size, septation, and number per ascus. This classification
largely ignored many features which (according to modern mycological concepts) now merit
careful consideration, although they were used to varying degrees for the delimitation of species
or infrageneric categories above this rank. In brief, these features involve the structure of asci,
excipular and hypothecial tissues, paraphyses and anamorphs, ontogeny, finer aspects of thallus
structure, and nature and location of pigments and lichen substances. In addition, investigations
of the phycobiont(s) and considerations of ecology and phytogeography often provide valuable
supplementary information. However, the use of some of these features in an attempt to define
more natural genera is not a purely recent phenomenon. Several lichenologists working in the
1850s and 1860s made bold attempts in this direction. With regard to the Lecideaceae s. lat., two
lichenologists deserving special mention are G. W. Korber (who introduced Lecidella, Lopadium,
Pyrrhospora, Schaereria, Schadonia, and Steinia) and A. B. Massalongo (who introduced
Catillaria, Psilolechia, Sarcosagium, Scoliciosporum, Strangospora, and Toninia). In the latter
half of the 19th century lichenology came under the almost monarchical influence of William
Nylander, whose simplistic generic concepts gained precedence over the more far-sighted works
of Korber, Massalongo, and others. From the 1870s right up to the 1950s there were few
attempts to reassess the generic concepts of Nylander or the slightly more complex, but no less
artificial, system of Zahlbruckner. Between about 1929 and 1954 the French lichenologist M. G.
B. Choisy resurrected many of the old and more or less forgotten genera, and created several
new ones (e.g. Haplocarpon [= Huilia], Hypocenomyce, Trapelia, and Tremolecia). Unfortu-
nately, Choisy's works made little impact at the time and it was not until the mid-1960s that
lichenologists began to look more carefully at the delimitation of genera. Recent investigations
have led to the reinstatement (although often with emendations) of many of these genera and
many new genera have had to be described (e.g. Fuscidea, Herteliana, Melanolecia, Trapeliop-
sis, Tylothallia, and Vezdaea). Most are included in the key to European lichen genera in Poelt
& Vezda (1981). Despite the many advances made during the last 15 years, it will be several
decades before a reasonably natural generic classification within the Lecideaceae s. lat. is
achieved. The enormity of the task can be appreciated from the fact that Zahlbruckner
(1921-40) accepted no less than 1450 species in the genus Lecidea alone! In addition to the high
number of taxa involved , further problems arise from the locating and obtaining on loan suitable
(including type) material, and the many difficulties in observing and interpreting many
microscopical, morphological, and ontogenetic features.