Hypoxylon fragiforme










Hypoxylon fragiforme (Pers.: Fr.) J. Kickx.

Stromata hemispherical to nearly spherical, frequently with conspicuous perithecial mounds, 2-9 mm diam x 1.5-7 mm high; surface rust (39) to bay (6), with orange-red granules beneath surface yielding KOH-extractable pigments orange (7), in early stages underlined by a conspicuous layer of white granules in which perithecia develop; the tissue below the perithecial layer black, massive, up to 6mm thick, extending upwards between the perithecia when aged.

Perithecia obovoid, 250-380 µm diam x 450-650 µm high.

Ostioles lower than or at the same level as the stromatal surface, black.

Asci 135-180 µm total length x 7-10 µm broad, the spore bearing-parts 64-92 µm long, the stipes 60-96 µm long, with apical ring amyloid, discoid, 1-1.3 µm high x 2.5-2.8 µm broad

Ascospores dark brown, ellipsoid-inequilateral, frequently crescent-shaped, 10-15 x 4.8-6.8 µm (M = 12.4 x 5.7 µm), with germ slit spore-length; perispore dehiscent in 10% KOH, smooth.

Anamorph in nature hazel (88), velvety, covering young stromata in early stages. Conidiogenous structure hyaline to slightly pigmented, roughened, Nodulisporium-like.Conidiogenous cells 15-27 x 3.3.5 µm. Conidia ellipsoid to nearly globose, 4-4.8 x 3.5-4 µm.

Habitat: primary saprophyte on corticated branches or wood of Fagus sylvatica. Also occasionally recorded on Alnus, Betula, Carpinus, Populus, Quercus, Sorbus and Tilia (Enderle 1982, Petrini & Müller 1986, Kriegelsteiner 1989, present study).

Known distribution: Europe and North America.

Specimens examined: FRANCE, Aričge (09) : Alzen, les Sauris, 24 Mar. 2001, JF-01045, on Betula pendula ; Aulus, chemin de la cascade d'Ars, 900m, 10 Sept. 2004, JF-04204, on Quercus, mixed with H. howeianum; Nalzen, 28 Jun. 2001, JF-01123, on Fagus sylvatica ; Orlu, les Forges, 950 m, 19 Mar. 2003, JF-03171, on Tilia sp.; Orlu, Réserve nationale d'Orlu, Jasse de Justiniac, 29 Jul. 2001, JF-01160, on Fagus sylvatica ; Prat Communal, Loumet, 1000m, 25 Aug. 2004, JF-04186, on Populus cf. nigra; Rimont, Las Muros, 03 Jul. 1996, JF-96049, on Fagus sylvatica; Rimont, Grand Bois, 22 Feb. 1999, JF-99033, on Fagus sylvatica; Rivčrenert, Forźt de Fachan, Col de la Crouzette, 1200 m,18 Jul. 2004, JF-04150, on Sorbus aucuparia, associated with H. multiforme; Ustou, Cirque de Cagateille, 1300 m, 26 Aug. 2001, JF-01172, on Fagus sylvatica, mixed with H. howeianum.

Notes: Hypoxylon fragiforme is a very common primary saprophyte of Fagus sylvatica, soon invading corticated branches or trunks after they have been cut off or broken. Its presence as latent invader in small pockets within healthy wood was demonstrated by Chapela & Boddy (1988a; 1988b).

It is distinctive in having hemispherical rusty stromata with orange-red granules beneath surface and orange KOH-extractable pigments, with a layer of white granules between perithecia when young, and in growing typically on Fagus sp. Host specificity of H. fragiforme appears less narrow than usually assumed in mixed beech woods where it can easily jump to other hosts.

It can be easily confused with H. howeianum which has very similar stromata and which, although usually growing on various hosts, has been occasionally recorded on Fagus and sometimes mixed with it (Petrini & Müller, 1986; present study). A reliable identification of H. fragiforme, even on Fagus, therefore needs checking ascospores size. Hypoxylon howeianum differs mainly from H. fragiforme in having smaller ascospores (7-9 x 3.5-5 µm) and in being associated with a conspicuous anamorph growing on radiating hyphal chords at base of young stromata.

Hypoxylon commutatum resembles H. fragiforme in stromatal shape and colour, but differs in having smaller ascospores (9-11 x 4.5-5 µm), in lacking ascal apical ring and in being possibly restricted to Carpinus.

Secondary metabolites recorded by HPLC in H. fragiforme and allied taxa including H. howeianum are mitorubrin and derivatives, along with orsellinic acid. Hypoxylon species of the fragiforme chemotype differ from other Hypoxylon species with orange KOH-extractable pigments in lacking BNT and rubiginosins (Mühlbauer et al., 2002; Hellwig et al., 2004; Stadler et al., 2004b).