Since the works of Greenhalgh & Whalley
(1970), Whalley & Greenhalgh (1971),
Steglich et al. (1974),
Whalley & Whalley (1977),
O'Hagan et al. (1992),
Adeboya et al. (1995),
Whalley and Edwards (1995),
Hashimoto & Asakawa (1998),
some members of the Xylariaceae were known
for their ability to yield specific compounds, isolated from stromata or
from cultures. The taxonomic value of these metabolites at the genus, species-group
or species level was already recognized by these authors as a promising way
to elucidate affinities within this family and discriminate closely related
taxa.
The results of recent investigations on
members of Xylariaceae carried out by
Mühlbauer et al. (2002),
Quang et al. (2002, 2003 a, 2003 b, 2004),
Stadler et al. (2001a, 2001b, 2004a, 2004b) and
Hellwig et al. (2005) all illustrate the high diversity
of secondary metabolites and their taxonomic value. High Performance Liquid
Chromatography (HPLC) combined with very accurate techniques of separation performed
by Stadler et al. (2001a, 2001b)
allowed for secondary metabolite profiling
in most of genera in Xylariaceae, with emphasis on Daldinia and Hypoxylon
which are most inventive genera as to secondary metabolites.
It is interesting to notice that in most cases,
HPLC results confirmed recent delimitations of xylariaceous genera or species
based on morphological anamorphic and teleomorphic data
(Petrini & Müller, 1986;
Ju & Rogers, 1996;
Ju et al., 1997) and, in addition, shed some light on expected or sometimes unexpected affinities
between distinct genera or species. HPLC is also much interesting in allowing
for secondary metabolites profiling of type material, for it can be performed
at micro- scale on samples of 10-50 µg, even on very old specimens such as the
type of Rhopalostroma africanum collected in 1814 or that of Hypoxylon
cohaerens collected prior to 1797!
(Stadler et al., 2004a;
Quang et al., 2005).
The identification of more recent collections with the type
material therefore becomes possible, even when the type is depauperate
and lacks some distinctive morphological characters. The limits of this
method appear when the herbarium material has been invaded by moulds producing
their own metabolites, or when preservative treatments involved artefacts able
to mask the genuine metabolites.
Unlike the former genera which are associated
with Nodulisporium-like anamorphs, xylariaceous genera with Geniculosporium-like
anamorphs (primarily Xylaria, Nemania, Rosellinia) lack stromatal
pigments and characteristic metabolites, except in one case for N. serpens
(Stadler et al. 2001b). However, they often produce more
or less specific compounds in culture
(Adeboya et al. 1995;
O'Hagan et al. 1992), but
for the moment, chemotaxonomy of those genera is much less understood. Efficient
chemotaxonomic methods will hopefully appear for genera like Xylaria,
for which the morphological approach often proves unrewarding.
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