Hypoxylon cercidicolum











Hypoxylon cercidicolum (Berk. & M.A. Curtis ex Peck) Ju & Rogers.

Stromata discoid, erumpent from bark, 3-15 mm diam x 1-1.5 mm thick, conspicuously encircled with a rounded stellate margin of fungal tissue covering the ruptured and turned down cortical periderm, sometimes coalescent, usually wrinkled between inconspicuous to conspicuous perithecial mounds; surface dark brick (60) to sepia (63); orange to orange brown granules beneath surface with KOH-extractable pigments orange (7) to sienna (8); the tissue below the perithecial layer inconspicuous or up to 700 m, dark brown.

Perithecia obovoid to infrequently tubular, 250-500 m diam x 650-700 m high.

Ostioles lower than the stromatal surface, surrounded by a ring of white substance 90-120 m diam.

Asci 140-175 m total length x 8-9 m broad, the spore bearing-parts 60-93 m long, the stipes 80-88 m long, with apical ring absent, inamyloid.

Ascospores brown to dark brown, ellipsoid-inequilateral, often broadly crescent-shaped, 9.5-11.5 x 4.8-6.2 m (M = 10.6 x 5.3 m), with faint straight germ slit spore-length; perispore dehiscent in 10% KOH, smooth.

Anamorph in nature is Hadrotrichum pyrenaicum O. Petrini & Candoussau (1983), growing on immature stromata, dark brick (60) frequently with olivaceous (48) tinge, deeply wrinkled. Conidiogenous cells hyaline to light brown, 10-15 x 3-4 m; conidia ellipsoid, light olive brown, 6-7 x 4-5 m.

Habitat: on bark of dying or dead branches of Fraxinus still attached to the tree.

Known distribution: Central and southern Europe (Czech Republic, France, Switzerland) and North America (Canada, USA).

Specimens examined: FRANCE, Arige (09): Castelnau Durban, Douach, 19 Feb. 1998, JF-98023, on Fraxinus excelsior; Rimont, Las Muros, 30 Sept.1996, JF-96090, on Fraxinus excelsior; Rimont, ruisseau de la Maille, 16 Jul. 1998, JF-98081, on Fraxinus excelsior ; Rimont, Las Muros, 20 Oct. 2001, JF0-1129, on Fraxinus excelsior.

Notes: Both immature stromata bearing the anamorph and fertile stromata with ascigerous perithecia are highly distinctive among other Hypoxylon taxa in being discoid and encircled with a swollen stellate margin that forms on the surrounding ruptured cortical periderm. Nevertheless, if immature stromata of H. cercidicolum are frequent in suitable stations, mature stromata containing fertile perithecia occur much more rarely and collecting them remains exceptional.

Hypoxylon cercidicolum grows on dying branches before they fall down to the ground and is restricted to Fraxinus. It occurs in shadowy and damp places and usually stops growing when branches are in contact with the soil, as also do H. intermedium (on Fraxinus) and H. laschii (on Populus).

Microscopically, H. cercidicolum is characterized by lacking ascal apical ring, a feature shared by H. intermedium and H. commutatum. They both mainly differ from H. cercidicolum in having pulvinate to hemispherical stromata.

Hypoxylon cercidicolum was described as H. moravicum Pouzar by Pouzar (1972), in a sense which fits perfectly the material examined for this study, but Ju and Rogers (1996) assessed it was identical with Diatrype cercidicola Berk. & M.A. Curtis ex Peck and its synonym H. suborbiculare Peck. In order to avoid confusion of H. cercidicolum ss Ju & Rogers with H. rubiginosum (Pers.: Fr.) Fr. var. cercidicola (Berk. & M.A. Curtis ex Peck) Petrini (Petrini & Mller, 1986) and H. cercidicola ss. Granmo, the taxon represented by these two latter names was now named H. petriniae Stadler & Fournier (Stadler et al., 2004b)

The results of HPLC analyses of H. cercidicolum (Stadler et al., 2004b) show it contains large amounts of mitorubrin, along with rubiginosin A and rubiginosin C, and traces of mitorubrinol and orsellinic acid, while the type material of H. suborbiculare shows only rubiginosin C and traces of mitorubrin and orsellinic acid, and unknown compounds that are probably artefacts due to preservative treatment. Both fungi are closely related but for the moment, HPLC results are not conclusive enough to consider they are conspecific. Fresh collections of H. cercidicolum from USA should allow for a better comparison. Nevertheless, their lack of BNT provided evidence for the specific status of H. petriniae