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2. Taxonomic part 24
Frisch (2006) distinguishes three different exciple types in his revised generic concept,
which, however, include the presence or absence of lateral paraphyses. Accordingly, in
Myriotrema and Fibrillithecis an ‘Ocellularia-type’ exciple is present, a ‘Leucodecton-type’
exciple is found in Leptotrema and Leucodecton, and a ‘Thelotrema-type’ exciple is
characteristic for the genera with chroodiscoid ascomata and Thelotrema and Topeliopsis.
(For further comments and explanations of the exciple-types see under chapter 2.9., but see
also in Frisch [ibid.]).
Subhymenium and hypothecium: The subhymenium is predominantly indistinct,
evanescent to thin, rarely thick, and usually concolorous with the proper exciple, but
sometimes also conspicuously dark pigmented. In some species with regenerating ascomata, a
distinct, hyaline, gelatinous I+ purple hypothecial area can be present, which represents newly
developing hymenial tissue.
Hymenium: The colorless, non-amyloid hymenium in thelotrematoid lichens is discoid to
cupular, clear to inspersed, weakly to strongly conglutinated and can be from c. 50 to 400 µm
high. The paraphyses are simple to slightly branched, c. 1-3 µm thick, straight to ±bent or
apically curly, parallel to ±interwoven. Sometimes also irregular paraphyses with a distinct
septation occur. The paraphyses tips are either not thickened or ±distinctly thickened and
simple to ±irregular. As mentioned above, all of the here treated species lack a columella.
Nevertheless, columella-like structures often occur in species with strongly fused ascomata
and resemble excipular tissue.
Lateral paraphyses: Lateral paraphyses (following Henssen, 1995) (‘periphysoids’ in
Frisch [2006]) are present or absent. They are mostly clearly separated from the proper
exciple, but sometimes also basally difficult to distinguish from it. They are predominantly
clear, very rarely interspersed and range from up to c. 10-50 µm in length. Although the
presence of lateral paraphyses is usually easy to recognize, in some cases inconspicuous and
easily overlooked lateral paraphyses occur.
Epihymenium: An epihymenial layer is variously developed, it is indistinct to very thick,
predominantly hyaline to more rarely yellowish or brownish, in Chroodiscus australiensis
conspicuously orange to reddish. It can be egranulose to distinctly granulose, the granules are
fine to coarse and grayish to brownish.
Ascus: The asci are 1-, 2-, 4- or 8-spored, non-amyloid, unitunicate and clavate. The ascus
walls are usually not thickened and a ±distinct tholus with an absent to small, tapered to
roundish ocular chamber is developed. The tholus mostly becomes, particularly in asci
bearing large ascospores, ±indistinct in later stages of development. However, several deviant
forms of asci could be observed and the taxonomical relevance of this feature is unclear.
Frisch (2006) lists up to five main ascus-types, and for the re-introduced genus Leptotrema he
considers the ascus morphology as a main delimiting character. In my observations, I could
find inconsistencies in several taxa, a ‘Leptotrema-type’ ascus (distinct tholus absent, ascus
walls evenly thickened in younger stages, thin at maturity) could also be found in other
genera, for example in Chapsa (C. lamellifera), Leucodecton (L. compunctellum), Myriotrema
(M. frustillatum) or Thelotrema (T. oleosum); a tholus with a large, distinctly tapered ocular
chamber, reported for Chapsa eitenii and C. zahlbruckneri (Frisch ibid.) also occurs in M.
protoalbum (see also table 4).
Ascospores: The ascospores occur uni- to triseriate, rarely quadriseriate, range from 6 up to
400 µm in length and form 2 up to 55 µm in width. They can be transversely septate or