Hypoxylon subticinense

              

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JF00135

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JF00135

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JF96184

JF96184

JF96184


Hypoxylon subticinense Ju & Rogers.

Stromata discoid to effused-pulvinate, frequently coalescent, with inconspicuous to infrequently conspicuous perithecial mounds, 6-35 mm diam x 1-1.6 mm thick; 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, 0.5-1.2 mm thick.

Perithecia obovoid to tubular, 200-300 m diam x 400-580 m high.

Ostioles lower than or at the same level as the stromatal surface, at the centre of a black discoid area 40-80 m diam.

Asci 145-170 m total length x 6-7.5 m broad, the spore bearing-parts 60-77 m long, the stipes 80-96 m long, with apical ring discoid, amyloid, 1-1.2 m high x 2-2.8 m broad.

Ascospores brown, ellipsoid nearly equilateral, 8-11.5 x 4-5.5 m (M = 9.7 x 4.7 m), with straight germ slit spore-length; perispore indehiscent in 10% KOH, smooth.

Anamorph in culture: ochreous (44), velvety, growing on young stromata. The conidiogenous structure is Virgariella-like. Conidiogenous cells yellowish to rusty, finely to coarsely roughened,16-47 x 2-4.8 m; conidia ellipsoid, hyaline, 3.5-5.5 x 2.8-3.5 m. Chlamydospores globose to ellipsoid, coarsely incrusted, rusty, 4-6 m diam, originating from the wall of conidiophores and from incrusted hyphae 2.8-3.5 m wide.

Habitat: on bark or decorticated wood of various hosts. Found on rotting wood lying on the ground (Acer campestre, Baccharis halimifolia, Hedera helix, Malus sylvestris, Fraxinus excelsior) or on dead branches hanging above the soil level (Populus tremula, Quercus ilex) or on dying shrubs (Rhamnus catharticus).

Known distribution: France (Arige, Charente Maritime, Morbihan, Pyrnes Atlantiques) and USA.

Specimens examined: FRANCE, Arige (09): Rimont, Las Muros, 30 Dec. 1996, JF-96184, on Populus tremula; Rimont, Las Muros, ruisseau de Peyrau, 26 May 1997, JF-97075, on Fraxinus excelsior; Rimont, Las Muros, ruisseau de Peyrau, 07 Nov. 1998, JF-98181, on Acer campestre; Rimont, Las Muros, ruisseau de Peyrau, 08 Feb. 1999, JF-99036, on Rhamnus catharticus; Rimont, Las Muros, ruisseau de Peyrau, 28 Jul. 2000, JF-00135, on Rhamnus catharticus; Rimont, Las Muros, 25 Sept. 2000, JF-00223, on Malus sylvestris. Charente Maritime (17): Ile de R, Fort du Lizay, Petit bec, 28 Apr. 2004, JF-04075, on Quercus ilex. Morbihan (56): Guidel, Locmaria, 24 Oct. 2002, JF-02198, on Hedera helix. Pyrnes Atlantiques (64): Anglet, Chiberta, Jun. 1993, FC-276, leg. FC and G. Gilles, on Baccharis hamilifolia.

Notes: Hypoxylon subticinense is strikingly similar to H. ticinense in stromatal colours and shape; moreover, it has similar KOH-extractable pigments and similar small-sized perithecia seated on a thick basal layer. It differs from H. ticinense in having larger and equilateral ascospores with perispore indehiscent in KOH, in having ostioles at the centre of a black discoid area on mature stromata and in some details of anamorphic morphology (Ju & Rogers, 1996).

Ju and Rogers (1996) describe the ostioles as sometimes higher than the stromatal surface but we did not observe this feature in the specimens we collected.

HPLC analyses reinforce the distinction of the two species, showing  that H. subticinense belongs to the rubiginosum chemotype, characterized by large amounts of mitorubrins and derivatives associated to orsellinic acid and specific azaphilones, while H.ticinense belongs to the fragiforme chemotype lacking azaphilones (Hellwig et al., 2004; Stadler et al., 2004b). Rubiginosins A and C present in H. subticinense are lacking in  H.ticinense, which, on the other hand, contains mitorubrinol acetate lacking in H. subticinense.

Hypoxylon subticinense has been rarely recorded and its ecology is poorly known. Although it may be found, as H. ticinense, on rotten wood lying on the ground, its occurrence on standing dying shrubs or on dead branches that are not in contact with the soil, providing that the air is humid enough, is noteworthy and may be useful in distinguishing it in the field from H. ticinense.