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Hypoxylon petriniae Stadler & Fournier
Stromata elongate to irregularly effused on wood or bark of Fraxinus,
plane, with inconspicuous perithecial mounds, usually finely wrinkled,
6-60 (-120) mm long x 3-22 (-25) mm broad x 0.3-0.8 mm thick; margins
black and linear, surface pale purplish grey (127), vinaceous grey (116),
vinaceous purple (101), dark vinaceous (82)
to brown vinaceous (84); yellowish brown, orange (7) to rust (39) granules beneath
surface and between perithecia with KOH-extractable pigments orange (7) or rust
(39); the tissue below the perithecial layer inconspicuous, up to 0.4 mm, dark
brown to blackish.
Perithecia spherical to obovoid, 250-380 µm diam x 250-500 µm high.
Ostioles umbilicate, on mature stromata frequently surrounded by a
ring of white material 50-70 µm diam.
Asci 115-145 µm total length x 7-10 µm broad, the spore-bearing parts
65-85
µm long, the stipes 37-64 (-72) µm long, with apical ring amyloid, discoid,
0.8-1 µm high x 2.7-3.4 µm broad.
Ascospores brown, ellipsoid-inequilateral to slightly falcate, 8.8-11.5
(-13) x 4.8-6 µm, M = 10.7 x 5.1 µm, with straight germ slit spore-length; perispore
dehiscent in 10% KOH, appearing smooth by L. M., but showing conspicuous transverse
striations by SEM (Stadler et al., 2004b).
Anamorph in nature: at margins of young stromata or on old stromata, velvety, buff
(45) to honey (65). Conidiogenous cells yellowish to light brown, smooth, 10-30 x
2-3 µm; conidia ellipsoid, 7-8 x 3-4 µm. The conidiogenous
structure is Virgariella-like, as confirmed by culturing on OA
(Stadler et al., 2004b) .
Habitat: frequently on bark, more rarely on wood of dead branches
still attached to the trunk or lying on the ground. A common saprophyte of Fraxinus
excelsior, but also occasionally found on Acer monspessulanus, Populus
tremula, Salix sp.
Known distribution: Probably widespread in Europe. Known from
France, Germany, Norway (Granmo 1999, as H. cercidicola), Switzerland
and U. K. (Petrini & Müller, 1986, as H. rubiginosum var.
cercidicola).
Specimens examined: FRANCE. Ariège (09):
Rimont, Las Muros, 10 Sept. 1996, JF-96094, on
Fraxinus excelsior; Rimont, Binette, 26 Apr.
2000, JF-00044, on Fraxinus excelsior; Rimont, Las Muros, 02
Aug. 2000, JF-00140, on Fraxinus excelsior; Rimont, Las
Muros, 02 Sept 2000, JF- 00180, on Fraxinus excelsior, associated
with H. rubiginosum;
Rimont, Las Muros, 19 May 2001, JF-01096, on
Fraxinus excelsior (isotype); Rimont, Grillou, 19 May 2001, JF-01097,
on Fraxinus excelsior; Rimont, Las Muros, 16 Aug. 2003, JF-03139,
on Populus tremula, associated with H. perforatum, H. rubiginosum
and Eutypa sparsa. Prat Communal, Loumet, 1000m, 03 Sept. 2004,
JF-04215, on Salix sp.Saint Jean de
Verges, Villeneuve du Bosc, 13 Dec. 1998, JF-98210, on Fraxinus
excelsior. Deux Sèvres (79): Virollet , Forêt de Chizé, 27
Apr. 2004, JF-04046, on bark of Acer monspessulanus. Finistère
(29): Plohars, Pont Douar, Forêt de Carnoët, 26 Oct. 2002, leg P.
Leroy, JF-02204, on Fraxinus excelsior. Loir et Cher (41):
St Georges du Cher, Camping, 17 Nov. 2003, PL-2467A, leg. P. Leroy, on Fraxinus
excelsior. Pyrénées Atlantiques (64): Auterrive,
Ile du Gave d'Oloron, 06 Nov. 2003, JF-03225, on Fraxinus excelsior.
Vendée (85): Avrillé, Bois de la Garde, 05 Jun. 2003, JF603091,
on Fraxinus excelsior.
Notes: Hypoxylon petriniae is a new name given to a common
and widespread fungus previously known as H. rubiginosum var. cercidicola
(Petrini & Müller, 1986)
and H. cercidicola
(Granmo, 1999). Both species concepts
referred to Diatrype cercidicola Berk. & Curtis ex Peck and H.
suborbiculare Peck, a later name given by Peck, based on better material,
to the fungus he first identified
to D. cercidicola.
On the other hand,
Ju & Rogers (1996),
refering to the same type collections, erected H.
cercidicolum to replace H. moravicum Pouzar
(Pouzar, 1972), and included
the fungus corresponding to H. rubiginosum var. cercidicola sensu Petrini
& Müller within their concept of H. rubiginosum. The epithet
cercidicola became therefore ambiguous, while the morphological
differences of the variety cercidicola with
H. rubiginosum pointed out by Petrini & Müller and
Granmo were sound enough to consider H. rubiginosum sensu Ju & Rogers
as an assemblage of two different species, one with vinaceous stromatal surface,
the other one with rust stromatal surface.
HPLC profiling of material of Hypoxylon species from France, Germany,
Switzerland and United Kingdom, along with the type of H. suborbiculare Peck.,
allowed for a better understanding of this nomenclatural situation which is
much confused from the beginning
(Stadler et al., 2004b).
The species with thin, vinaceous stromata called H. rubiginosum var. cercidicola
or H. cercidicola
proved to differ from the typical
H. rubiginosum in lacking mitorubrin and in containig BNT, while they
both contain rubiginosins A and C. H. petriniae appears to be the only
temperate species with both BNT and rubiginosins. This striking difference of secondary
metabolites, along with morphological differences reporded by
Petrini & Müller (1986) and
Granmo (1999),
and evidence of a Virgariella-like anamorph
(Stadler et al., 2004b)
versus a Nodulisporium-like in
H. rubiginosum
(Ju & Rogers, 1996)
confirmed this species was different from
H. rubiginosum. In order
to avoid further confusions related to the epithet cercidicola, this
species was named H. petriniae in honour of Liliane Petrini who first
recognized the peculiarities of this taxon
(Stadler et al., 2004b).
HPLC analyses also proved H. suborbiculare lacks BNT, a very stable
metabolite which can be detected from very aged material, and therefore cannot
be a synonym of H. petriniae. However, the results of HPLC analyses
of Peck's material are not fully conclusive, for they revealed the presence
of prevailing unknown metabolites that could be artefacts due to a preservative
treatment, along with rubiginosin C and traces of mitorubrin and orsellinic
acid. These results are slightly deviating from those obtained from fresh material
of H. cercidicolum sensu
Ju & Rogers (1996) (= H. moravicum
Pouzar) in which mitorubrin is the prevailing metabolite along with rubiginosin
A. The question of the identity of
H. cercidicolum is still pending until
fresh material corresponding to H. suborbiculare is found in North America
and submitted to HPLC
(Stadler et al., 2004b).
Hypoxylon petriniae is readily distinguished from other Hypoxylon
species with effused vinaceous brown stromata in having orange KOH-extractable
pigments. Moreover, its thin stromata with usually black margins and a marked
host preference for Fraxinus make it a rather distinctive taxon. These
subtle morphological differences are more obvious when it is found growing close
to H. rubiginosum or
H. perforatum on a same branch, which occurs
sometimes and provides a good training to the field mycologist..
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