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Hypoxylon julianii L. Petrini.
Stromata effused on wood, effused-pulvinate on bark, with
inconspicuous to infrequently conspicuous perithecial mounds, 3-40 mm long
x 2-11 mm broad x 0.5-1 mm thick; surface dark brick (60) to sepia (63),
often with a sienna (8) or greyish sepia (106) tinge, with sienna (8) to black
effused margins; red granules beneath surface and between
perithecia, with KOH-extractable pigments apricot (42) to sienna (8);
the tissue below the perithecial layer brown to reddish brown,
inconspicuous or up to 0.3 mm.
Perithecia spherical to obovoid, rarely on two layers, (200-)
250-320 µm diam.
Ostioles lower than or at the same level as the stromatal
surface, at the centre of a black discoid area 50-90 µm diam.
Asci 135-200 µm total length x 8-12 µm broad, the spore
bearing-parts 96-124 µm long, the stipes 37-80 µm long, with apical ring
amyloid, 1.5-2.8 µm high x 3.5-4.8 µm broad.
Ascospores brown to dark brown, ellipsoid-inequilateral, 15-20.4
x 6.2-8.4 µm (M = 17.2 x 7.2 µm), with straight germ slit spore-length;
perispore indehiscent in 10% KOH, smooth.
Anamorph in nature: on young stromata, velvety, vinaceous buff
(86) to fawn (87). Conidiogenous cells hyaline to light brown, smooth, 10-40 x
2-3 µm; conidia broadly ellipsoid, 4-4.8 x 3-3.5 µm. The conidiogenous
structure is Virgariella-like.
Habitat: on wood or bark of various deciduous trees, usually on
dead wood in damp and shadowy places, in contact or not with the soil.
Recorded during this study on Acer campestre, Castanea sativa,
Corylus avellana, Fagus sylvatica, Juglans regia, Populus tremula, Robinia pseudoacacia, Salix
caprea, Ulmus minor. The type collection was reported on Alnus
incana
(Petrini & Müller, 1986).
Known distribution: Europe; known from Denmark
(Laessøe, 1998),
France (Ariège and Haute Garonne) and Switzerland.
Specimens examined: Ariège (09): Montseron,
Roquebrune, 09 Mar. 2001, JF- 01034, on Salix
caprea; Quérigut, route du Laurenti, 23 Aug. 1998, JF-98119, on
Fagus sylvatica; Rimont, Las Muros, ruisseau de Peyrau,
30 Oct. 1996, JF-96129, on Acer campestre; Rimont, La Mijane,
ruisseau de Peyrau, 13 Jul.1997, JF-97094, on Populus
tremula; Rimont, Las Muros, ruisseau de Peyrau, 29 Jun. 1999,
JF-99134, on Ulmus minor; Rimont, Las Muros, 15 Apr. 2001,
JF-01071, on Populus tremula; Vernajoul, Pont Fagé, ruisseau
de Vernajoul, 31 Aug. 2001, JF-01187, on Corylus avellana.
Haute Garonne (31) : Saleich, Artihaguère, 09 Nov 1998,
JF-98178, on Castanea sativa.
Notes: Hypoxylon julianii was previously only known from two
collections on Alnus incana in Switzerland
(Petrini & Müller, 1986). Its recent reports from Denmark
(Laessøe, 1998) and from Central
Pyrénées (present study) shows that it probably could be recorded in other parts of Europe if
attention was paid to it.
In the field, its discrete stromata are easily overlooked or confused
with those of H.
rubiginosum or H. rutilum
which both also have orange brown stromata with orange KOH-extractable
pigments. Moreover, it shares with H. rutilum
similar black ostioles, opening at times higher than the stromatal
surface, red granules beneath surface and small-sized spherical
perithecia, but differs in lacking the distinctive sweetish smell of
H. rutilum
and in having much larger ascospores. It is more easily distinguished from
H.
rubiginosum which have larger perithecia with ostioles opening
lower than the stromatal surface, orange granules beneath
surface and much smaller ascospores.
Red granules beneath stromatal surface of H. julianii are
usually conspicuous on young stromata, especially at stromatal margins,
but often become inconspicuous on mature and old stromata, thus ascospore
dimensions remain the more diagnostic feature of this taxon.
Similar ascospore size range is found in H.
ferrugineum Otth, which differs from H. julianii in having pulvinate
stomata constricted at base and erumpent from bark, and with host preference
for Tilia. Moreover its ascospores are averaging slightly shorter and
broader.
Our collections slightly differ from the original description in having
somewhat larger ascospores with perispore not dehiscing in 10% KOH. The
perispore of H. julianii is reported as very thin and difficult to observe
by Ju et al. (2004).
Additional collections from other regions might show
whether these variations have a taxonomic importance.
Secondary metabolites of H. julianii are mitorubrinol as prevailing
compound, along with rubiginosins A and C and orsellinic acid, which is typical
for the rubiginosum chemotype
(Hellwig et al., 2002;
Stadler et al., 2004b). Interestingly,
H. julianii and
H. rutilum,
which are so easily confused in the
field, have nearly identical HPLC profiles and even share a same unknown and specific
compound (peak HR1,
Stadler et al., 2004b).
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