Bulletin of the British Museum (Natural History)

LICHEN GENUS MICAREA IN EUROPE 67
mould (e.g. in the Metacapnodiaceae) which have three hyphomycetous anamorphs (Hughes
1972, 1976).
The main distinguishing features of the three conidium types found in Micarea are as follows
(see Figs 37-52 for example): Microconidia, narrowly cylindrical or narrowly fusiform, aseptate,
eguttulate and not constricted in the middle, mostly in the range 3-8x0-5-1 /Am; produced in
small immersed or ± sessile pycnidia, mostly c. 20-60 /xm diam. Mesoconidia, variable in shape,
e.g. cylindrical, oblong, ovoid-oblong or obovoid-oblong, aseptate, often biguttulate and (or)
slightly constricted in the middle; produced in small to large, immersed, sessile or stalked
pycnidia. All conidia found in stalked pycnidia are included here. Macroconidia, mostly fihform
or curved and often septate, or heUcoid and septate (M. subnigrata (p. 183)); produced in
medium-sized to large (often up to 200 jxm diam or more) pycnidia. Also included here are the
large, aseptate, eguttulate, oblong-ellipsoid conidia produced by the sporodochia of M. adnata.
In all cases no single pycnidium has been found to contain more than one conidium type. A
few specimens of M. denigrata and M. nitschkeana have been found with all three anamorphs on
the same thallus; but such occurrences are rare and it is more usual to find just one or two of
them. A few species (e.g. M. assimilata, M. crassipes, and M. incrassata appear to have only one
anamorphic state, with conidia somewhat intermediate between microconidia and mesoconidia
as defined above; thus the assignment of their conidia to one or other of these types (Table 1)
must be considered tentative. The distinction between the three conidium types (especially
micro- and mesoconidia) is most obvious when two or three of them occur on the same thallus.
The use of the terms 'micro-', 'meso-' and 'macroconidia' are here apphed solely to the conidium
types found in Micarea - they may not necessarily be analogous to their use in other lichenized or
non-lichenized fungi. Table 1 indicates the conidium type(s) known for each of the European
species of Micarea, and from this a numerical summary of the various known combinations is as
follows:
Combination of conidium types Number of species
(anamorphs) (holomorphs)
Micro- -I- meso- -I- macro- 3
Micro- + meso- 10
Micro- -I- macro- 5
Meso- -I- macro- 1
Micro- only 6
Meso- only
Macro- only
14
Anamorph(s) unknown 6
The role of each of the conidium types is as yet unknown. Vobis (1977) obtained successful
germination and subsequent growth of mycelium from the macroconidia of Lecanactis abietina,
but was unable to germinate the microconidia of the same species. His results suggest that the
former may well act as asexual propagules, and the latter as spermatia in sexual reproduction. It
seems most likely to me that the microconidia oi Micarea species are spermatia. As to whether or
not they are essential components of the sexual reproductive process is much less certain; 21 of
the treated species are not known to produce microconidia.
The role of conidia as asexual propagules is still a matter of much debate and speculation
among lichenologists, but such a role (at least in certain cases) can be inferred from the fact that a
few crustose species (e.g. Lecanactis subabietina and an undescribed Bacidia) are not known to
have apothecia or vegetative diaspores (i.e. soredia, isidia, etc.) but always have numerous
pycnidia. To such examples can be added the numerous crustose lichens whose apothecia are
known, but which commonly occur as sterile populations with numerous pycnidia, e.g.
Anisomeridium juistense (macroconidial state), Arthonia phaeobaea, A. spadicea, Bacidia
arnoldiana, B. carneoglauca, B. trachona, Cliostomum graniforme, C. griffithii, Lecanactis
abietina, Lecidea erratica, Opegrapha niveoatra, O. vermicellifera, and O. vulgata. This last
group also includes Micarea botryaides, M. denigrata, M. misella, M. pycnidiophora, and M.
stipitata, all of which commonly occur with abundant mesoconidia-containing pycnidia and few
(if any) mature apothecia.