Hypoxylon ticinense

              

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Hypoxylon ticinense L. Petrini.

Stromata discoid 10-28 mm diam,or effused-pulvinate 22-50 mm long x 10-19 mm broad x 1-1.5 mm thick, with inconspicuous perithecial mounds; surface irregular, undulating, surface sienna (8), rust (39), powdery when young with a villose, ochreous (44) to sienna (8) margin, becoming dark brick (60)  to sepia (63) when mature; orange granules beneath surface and between perithecia, with KOH-extractable pigments orange (7) to sienna (8); the tissue below the perithecial layer blackish brown to black, 0.5-1 mm thick.

Perithecia obovoid to tubular, 200-250 m diam x 250-500 m high.

Ostioles lower than the stromatal surface, infrequently surrounded by a ring of white material (25-) 40-60 m diam.

Asci 80-95 m total length x 4-5.5 m broad, the spore bearing-parts 34-53 m long, the stipes 40-72 m long, with apical ring weakly amyloid to amyloid, discoid, 0.3-0.5 m high x 1-1.5 m broad.

Ascospores light brown to brown, ellipsoid-inequilateral, 4.8-6.8 x 2.7-3.4 m (M = 5.9 x 2.9 m), with faint straight germ slit spore-length; perispore dehiscent in 10% KOH, smooth.

Anamorph in nature: ochreous (44), velvety, on young stromata. Conidiogenous cells yellowish, slightly roughened, 15-20 x 3-3.5 m; conidia broadly ellipsoid, 3.5-4 x 2.5-3m. The conidiogenous structure is Virgariella-like. The rusty powdery coating on immature stromata consists of coarsely incrusted orange hyphae 3.5-5 m wide, producing globose chlamydospores 4-5.5 m diam, yellow to orange.

Habitat: on wood or bark of various hosts, usually at the lower side of branches lying on the ground in damp places. Mostly found on Crataegus oxyacantha and Fraxinus excelsior, but occasionally recorded on Acer negundo, Corylus avellana, Malus sylvestris, Prunus spinosa , Salix caprea (present study), and on Sambucus nigra (Leroy & Surault 1999), likewise on "Negundo aceroides", Populus alba, "Padus avium"and "Swida sanguinea" (Ripkov & Hagara, 2003).

Known distribution: Europe: Croatia, Czech Republic (Ripkov & Hagara, 2003), France and Switzerland, probably more widespread in Europe.

Specimens examined: FRANCE, Arige(09): Rimont, Las Muros, 22 Sept. 1996, JF-96095, on bark of Crataegus oxyacanthae; Rimont, Las Muros, ruisseau de Peyrau, 25 Aug. 1999, JF-99205, on bark of Crataegus oxyacanthae; Rimont, Las Muros, 26 Jul. 2000, JF-00129, on a stump of Fraxinus excelsior; Rimont, Las Muros, ruisseau de Peyrau, 02 Sept. 2001, JF-01181, on bark of Fraxinus excelsior. Pyrnes Atlantiques (64): Maulon, les Barthes de l'Hpital Saint Blaise, 06 Jun. 1999, JF-99254, on Prunus spinosa; Maulon, les Barthes de l'Hpital Saint Blaise, 06 Jun. 1999, JF- 99255, on Corylus avellana.

Notes: Hypoxylon ticinense is a striking fungus, with distinctive stromata that are usually discoid, pulvinate, thick and undulating, surrounded when immature by a bright yellow to orange fimbriate margin. Perithecia are small-sized, often tubular and lie on a thick blackish basal tissue. These features are usually distinctive enough for its field identification but confusion is possible with H. subticinense which has a very similar stromatal morphology. The latter differs from H. ticinense in having larger ascospores which are ellipsoid-equilateral, with perispore indehiscent in KOH.

Another diagnostic feature could be the colour of the discoid area surrounding the ostioles, black in H. subticinense, absent or white in H. ticinense, but this should be checked on more material before being considered constant.

While they both contain mitorubrin and orsellinic acid as prevailing metabolites, the two latter species are readily distinguished by HPLC analyses: H. ticinense lacks the azaphilones rubiginosins A and C, and therefore belongs to the fragiforme chemotype, but contains mitorubrinol acetate which is lacking in H. subticinense (Hellwig et al., 2004; Stadler et al., 2004b).