Hypoxylon julianii

              

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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 m diam.

Ostioles lower than or at the same level as the stromatal surface, at the centre of a black discoid area 50-90 m diam.

Asci 135-200 m total length x 8-12 m broad, the spore bearing-parts 96-124 m long, the stipes 37-80 m long, with apical ring amyloid, 1.5-2.8 m high x 3.5-4.8 m broad.

Ascospores brown to dark brown, ellipsoid-inequilateral, 15-20.4 x 6.2-8.4 m (M = 17.2 x 7.2 m), 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 m; conidia broadly ellipsoid, 4-4.8 x 3-3.5 m. 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 & Mller, 1986).

Known distribution: Europe; known from Denmark (Laesse, 1998), France (Arige and Haute Garonne) and Switzerland.

Specimens examined: Arige (09): Montseron, Roquebrune, 09 Mar. 2001, JF- 01034, on Salix caprea; Qurigut, 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 Fag, ruisseau de Vernajoul, 31 Aug. 2001, JF-01187, on Corylus avellana. Haute Garonne (31) : Saleich, Artihagure, 09 Nov 1998, JF-98178, on Castanea sativa.

Notes: Hypoxylon julianii was previously only known from two collections on Alnus incana in Switzerland (Petrini & Mller, 1986). Its recent reports from Denmark (Laesse, 1998) and from Central Pyrnes (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).