Miscellaneous Contribution to the Anatomy and Molecular phylogeny of tropical African resupinate Thelephorales (Basidiomycota, Fungi)

The Thelephorales (Basidiomycota, Fungi) form a monophyletic group
with approximately 177 accepted species. The Thelephorales are
cosmopolitan and encompass mainly ectomycorrhizal species. Unlike
many fungal lineages, evolutionary trends within and between
members of Thelephorales still remain incompletely assessed.
Additionally, most phylogenetic investigations on fungi have failed
to include representative samples from tropical Africa. In the
present study started four years ago, we have assessed and
documented some of the diversity of tropical African Thelephorales.
It represents a part of a future broader but continuous project
aiming for a complete monograph, and highlighting the anatomical
and molecular relevance of tropical species in the evolutionary
interpretation of Thelephorales in general. The study was started
in the northern Guinean seasonal forests, located from central to
north Benin (West Africa). Northern Guinean seasonal forests are
characterised by a low specific plant richness, but predominated by
a few ectomycorrhizal trees of the Caesalpiniaceae (Isoberlinia
doka Craib & Stapf Isoberlinia tomenteosa (Harms) Craib &
Stapf, Burkea africana Hook., and Afzelia africana Smith),
Dipterocarpaceae (Monothes kerstingii Gilg.) and Euphorbiaceae
(Uapaca guineensis Müll. Arg.). Four collecting trips were
undertaken during the rainy seasons of 2003, 2004, 2005 and 2006.
Specimens of Thelephorales and soil cores were randomly sampled
under native ectomycorrhizal trees. The collecting trips yielded
over 800 specimens of Thelephorales and 60 EcM samples in total.
Taxonomic investigations and species concepts of the specimens were
assessed using a combination of both molecular and
anatomo-morphological approaches. All examined specimens were
sorted into 19 morphologically different species. In this
dissertation four new species are described and illustrated. A full
description is provided for each species, together with reliable
line drawings and, where possible, with SEM micrographs. Anatomic
studies have confirmed and emphasised the commonality of
irregularly shaped thin hyphae on the rhizomorph surfaces of many
African species. Novel anatomical features hitherto unknown within
Thelephorales, and rarely recorded for Hymenomycetes in general,
are recorded. Detailed anatomical comparison with type species has
enabled us to depict fundamental arguments about the discrimination
of thelephoroid genera. We report fundamental differences in spore
ornamentation between African and temperate tomentelloid species.
Using molecular PCR methods, we confirmed the high divergence rate
of the ITS regions of thelephoroid fungi. Within morphologically
close specimens, the ITS rDNA sequence deviation generally ranges
between 0.0 to 2.68%. However, genetic distance between some
specimens (e.g.Tomentella furcata Yorou & Agerer and T. cf.
furcata nom. prov.) illustrates how morphologically convergent
specimens may be greatly divergent with regard to their ITS rDNA.
Phylogenetically, tropical African species of Thelephorales are
either basal or terminal within various clades of investigated
temperate, boreal and tropical species. Generally, they highly
deviate from temperate and boreal closest species by 4.3 to 12.9%
with regard to the ITS rDNA sequences. Northern Guinean seasonal
forests harbour a great diversity of Thelephorales that are,
however, hard to detect due to the down-facing growth of fruit
bodies of most resupinate Thelephorales, and the annual burning of
required substrates. Only one species, Tomentella africana Yorou
& Agerer, is widespread and commonly recorded. Many other
species occur scarcely on fragmented substrates. Though the
Thelephorales are cosmopolitan, we failed to record species that
are reported to have a worldwide distribution. Notably,
representatives of the resupinate thelephoroid genera
Pseudotomentella Svrček and Tomentellopsis Hjortstam were missing,
as well as species of the mainly temperately distributed family
Bankeraceae. In this study, we provide evidence of the
ectomycorrhizal formation between Thelephorales and native tropical
African forest trees. Anatomical and molecular characterisation of
ectomycorrhizae formed between Thelephorales and native West
African forest trees (namely Afzelia africana and Uapaca
guineensis) are provided for the first time. The present studies
are based on original material collected in some Ceasalpinioid
/Euphorbiaceae-dominated vegetation types found from central to
north Benin. The Zambesian Centre of Endemism, located in
South-East Africa, also harbours a variety of different
ectomycorrhizal trees including Brachstegia spp, Julbernadia spp,
and Isoberlinia spp. Stands dominated by monospecific
ectomycorrhizal forest trees are also present in the rain forests
of South Cameroon. The variety of ectomycorrhizal tree species
present in tropical Africa implies a greater species richness of
Thelephorales than that currently reported from Benin. The present
thesis represents a keystone study and provides baseline data for a
continuing monograph of Thelephorales in tropical Africa. Intensive
monographic and taxonomical investigations will undoubtedly reveal
many interesting, and probably plesiomorphic, anatomical features
from tropical Thelephorales. In this context, detailed anatomical
investigations integrated with DNA sequence analyses and
phylogenetic inferences are promising tools for discriminating
thelephoroid species in general, and tropical ones in particular.
Taxonomic novelties in this study: Tomentella capitata Yorou &
Agerer Tomentella brunneocystidia Yorou & Agerer Tomentella
furcata Yorou & Agerer Tomentella africana Yorou & Agerer