SMT 1-2005 - Sveriges Mykologiska Förening

DNA
Line 3. Lecanoromycetes contains the majority of the
lichens. The asci have a layered wall, often with parts
of the ascus staining blue in Melzer´s Reagent. The
ascus in discolichens was referred to as of "type bitunique-archaeasce´"
by Chadefaud (1960, 1973) and
his co-workers. It was interpreted as an archaic type
of ascus, that evolved from the "préarchaeascé" type,
and from which other types of asci in ascomycetes
producing fruit bodies were derived. This has been
much debated (see Hohnegger 1978) and the
question has not yet been settled. It is probable,
however, that the different ascus types seen in lichens
developed during a long period and that the group is
old.
Two groups sometimes cluster with the
Lecanoromycetes in phylogenetic analyses. They
have been treated as the classes Chaetothyriomycetes
and Eurotiomycetes (Eriksson & Winka 1997), but
there is weak support for a close relationship with
Lecanoromycetes in some analyses (e.g. Lumbsch et
al. 2004). There is, on the other hand, a stronger
support for a close relationship between Chaetothyriomycetes
and Eurotiomycetes (Winka 2000,
Lindemuth et al. 2001) and they are merged in some
classifications and treated as subclasses of
Eurotiomycetes (Lutzoni et al. 2004, Eriksson 2005).
Chaetothyriomycetidae. This subclass has perithecialike
fruit bodies. The wall of the asci consists of two
layers and is amyloid (I+ = blue reaction with
Melzer´s reagent) in some species. Some have conidial
states that are harmful to humans (dermatophytes
etc.). Two large orders contain lichens,
Pyrenulales and Verrucariales. Sequences from many
families temporarily listed under Dothideomycetes
are not yet available and they may turn out to belong
in Chaetothyriomycetidae.
Eurotiomycetidae. This subclass has cleistothecia
with walls breaking up at maturity. The asci are globose,
lack opening mechanism and are scattered in
the inner parts of the fruit bodies (Currah 1985).
Many members of the class have conidial states
(Penicillium, Aspergillus, etc.) that are of positive
(penicillium, green cheese, etc.) or negative (cancerogenous
metabolites, destruction of food, etc.) economic
importance to humans. There are no lichenized
species. This subclass probably evolved from
some member(s) of the Chaetothyriomycetidae by
paedomorphosis.
Line 4. Lichinomycetes (Reeb et al. 2004) is a small
group with aberrant apothecia (perithecia-like) and
asci with very simple walls. Almost all are stone-
inhabiting lichens. They live in symbiosis with
cyanobacteria. Molecular data do not place this
group close to any other class and it may have evolved
directly from "protolichens".
Line 5. Leotiomycetes are non-lichenized discomycetes.
The apothecia have asci with thin walls, open by
a pore and often have an apical amyloid ring. Most
species in this large group are saprobes on herbs,
shrubs and trees, but there are some parasites as well.
One order (Erysiphales, powdery mildews) has
cleistothecia that probably evolved by paedomorphosis
from ancestors with apothecia. In some analyses
this class comes close to the next one, but more
molecular data are required to clarify this.
Line 6. Sordariomycetes have perithecia with thinwalled
asci, and many have an amyloid, apical ring.
This is a very large and diversified group of saprobes
and parasites on various plants, animals and other
organic substrates. There are no lichenized species.
Dothideomycetes have perithecia-like fruit bodies,
asci with double wall layers, very seldom with amyloid
reaction. Upon spore discharge the inner layer
streches like a "Jack-in-the-box" to the opening of
the fruit body and the spores are ejected. This is a
very large group of mainly saprobes on old leaves,
stems etc, and only a few species are lichens.
Arthoniomycetes have apothecia with very simple
wall structures, asci with double wall layers and often
with amyloid structures; most of the species are
lichens.
Were the Arthoniomycetes and Dothideomycetes
close to the early Sordariomycetes? And did the two
classes diverge from the main line with true perithecia
by arrested development of the early perithecial
cells to form stromata? Then one line resulted
in apothecia-like fruit bodies (Arthoniomycetes) and
the other one perithecia-like fruit bodies (stromatic
and named pseudothecia in Dothideomycetes; however,
apothecia-like in one order, the Patellariales). The
Arthoniomycetes kept the lichen life style, while in
Dothideomycetes only a few are lichenized. The
Arthoniomycetes kept the amyloid reaction of the
asci, whereas few in Dothideomycetes show this
reaction. The three classes are sometimes merged, but
too much is still unknown about the position of many
Dothideomycetes and the statistical support in phylogenetic
analyses is not strong.
32 SVENSK MYKOLOGISK TIDSKRIFT 26:1 (2005)