Hypoxylon carneum Petch.

Stromata effused on wood, more pulvinate on bark, widely to narrowly ellipsoid, 11-35 mm long x 3-15 mm broad x 0.4-0.5 mm thick; surface plane or irregular, with inconspicuous perithecial mounds,dark purple (36), dark vinaceous (83), dark livid (80, when young with white, pinkish or red brown effused margins; yellowish granules beneath surface and between perithecia, giving a greyish lilac (100) colour to the tissue beneath surface and between perithecia, with KOH-extractable pigments dilute livid violet (79), absent in aged material; the tissue below the perithecial layer inconspicuous to 200 µm thick, dark brown.

Perithecia spherical to obovoid, 200-300 µm diam x 250-350 µm high.

Ostioles lower than the stromatal surface, on mature stromata surrounded by a ring of white substance 60 µm diam.

Asci 85-120 µm total length x 7-7.5 µm broad, the spore bearing-parts 56-78 µm long, the stipes 25-55 µm long, with apical ring discoid, amyloid, 0.8-1 µm high x 2.5-2.8 µm broad.

Ascospores light brown to brown, ellipsoid nearly equilateral, 8.8-11 x 4-4.8 µm (M = 9.8 x 4.6 µm), with straight germ slit spore-length, at the centre of a darker band 1 µm broad; perispore dehiscent in 10% KOH, smooth.

Anamorph in nature: white, velvety, at margins or on young stromata. Conidiogenous cells hyaline, 10-20 x 2-3.5 µm; conidia ellipsoid, hyaline, 3.5-4.8 x 2-3 µm. Conidiogenous structure is Sporothrix-like.

Habitat: on wood or bark of branches and trunks of various hosts, in contact with the soil in damp places. Recorded during this study on Acer pseudoplatanus, Cornus sanguinea, Crataegus sp., Cydonia oblonga, Fraxinus excelsior, Malus sylvestris, Populus tremula, Prunus spinosa, Salix atrocinerea, Salix caprea, Sorbus torminalis, Tilia platyphyllos and Ulmus minor.

Known distribution: worldwide, reported from France (present study), New Zealand, Sri Lanka, USA and Venezuela (Ju & Rogers, 1996).

Specimens examined: FRANCE, Ariège (09): Rimont, Las Muros, ruisseau de Peyrau, 12 Sept.1999, JF-99213, on Salix caprea; Rimont, Las Muros, 27 Jun. 2000, JF-00103, on Ulmus minor; Rimont, Las Muros, ruisseau de Peyrau, 22 Sept.2000, JF-00209, on Ulmus minor; Rimont, Las Muros, 08 Feb. 2001, JF-01015, on Ulmus minor; Rimont, Las Muros, 06 Apr. 2001, JF-01061, on Sorbus torminalis. Haute Garonne (31): Montespan, Le Pont, 17 Jun. 2002, JF-02107, on Ulmus sp. Pyrénées Atlantiques (64): Mauléon, les Barthes de l'Hôpital Saint Blaise, 27 Oct. 1998, JF-98180, on Salix atrocinerea.

Notes: Hypoxylon carneum is distinctive in having small-sized effused stromata with a purplish tone, small-sized perithecia surrounded by a greyish lilac tissue yielding dilute livid violet pigments in 10% KOH, and equilateral ascospores with the germ slit at the centre of a darker band. This band is reported as dotted by Ju and Rogers (1996) but this feature is hardly visible under usual conditions. Another taxon with similar stromatal colour and germ slit morphology is H. vogesiacum (Pers.) Sacc. which differs in having much larger ascospores 20-25 x 8-10 µm.

Hypoxylon carneum may be confused with small effused stromata of H. petriniae, H. perforatum and H. fuscum. Both H. fuscum and H. perforatum differ in yielding olivaceous yellow pigments in 10% KOH and in having larger inequilateral ascospores, while H. petriniae is mainly different from H. carneum in having orange or yellow brown granules yielding orange pigments in 10% KOH.

Hypoxylon carneum, which has not previously been reported from Europe, is probably overlooked as it is easily confused with the common and widespread above species. Its disjointed distribution probably reflects its difficulty to be identifieded. In the field, a tangential section of the stromatal surface readily shows the greyish lilac tissue between the perithecia, which is diagnostic.

In their monograph, Ju & Rogers (1996) describe the stromata of H. carneum with chestnut surface and yellowish brown to reddish brown granules between perithecia without apparent KOH-extractable pigments

On the other hand, the stromatal surface of the type collection (Petch, 1924) is said to be pinkish and the interperithecial tissue of pale red or purple red hyphae, and that could more or less agree with our collections. Unfortunately this type materiel is ruined by mercuric chloride used as preservative (Miller, 1961), its stromatal features are no longer reliable and KOH-extractable pigments were not reported.

Despite these differences, Professor J. D. Rogers identified three of our collections as H. carneum (pers. comm.), relying on the peculiar morphology of ascospore germ slit. This identification was fully confirmed by comparison of HPLC profiles of type material from Sri Lanka with material from France and other locations (Stadler, pers. comm.). HPLC analyses reveal H. carneum stromata lack mitorubrin and other usual metabolites of Hypoxylon, but contain BNT and yet unknown compounds (Stadler, pers. comm.).