Hypoxylon rutilum Tul. & C. Tul.
Stromata pulvinate to nearly hemispherical when growing on bark,
erumpent through the lenticels, 3-12 mm long x 3-5 mm broad x 1-1.5 (-2)
mm thick, effused to effused-pulvinate when growing on decorticated wood,
4-23 mm long x 2-5 mm broad x 0.4-0.5 (-0.9) mm thick, with inconspicuous
to conspicuous perithecial mounds; surface sienna (8), rust (39) to dark
brick (60); orange red granules beneath
the stromatal surface and between the perithecia, with KOH-extractable
pigments orange (7) to scarlet (5); the tissue below the perithecial layer
blackish, inconspicuous or up to 100 µm thick; underlying wood with a
sweetish smell reminiscent of coconut.
Perithecia spherical to obovoid, 150-200 µm diam x 200-300 µm
high, the fertile perithecial layer may be seated on up to four layers of
old and empty perithecia.
Ostioles higher than the stromatal surface, black, minutely
Asci 145-160 µm total length x 6-7.5 µm broad, the spore
bearing-parts 55-75 µm long, the stipes 85-95 µm long, with apical ring
discoid, amyloid, 0.8-1 µm high x 2-2.8 µm broad.
Ascospores brown to dark brown, ellipsoid-inequilateral, 7.5-10
x 4-4.8 µm (M = 8.8 x 4.5 µm), with straight germ slit spore-length;
perispore dehiscent in 10% KOH, smooth.
Anamorph in nature: on young or old stromata, fawn (87) velvety.
The conidiogenous structure is Virgariella-like, pale
brown, roughened. Conidiogenous cells 21-27 x 2.5-3 µm; conidia
ellipsoid, hyaline, 3.5-5(-6) x 2.8-3.5 µm.
Habitat: on bark and wood of twigs and branches lying on the
ground in damp and shadowy places. Recorded on Alnus glutinosa, Corylus
avellana, Fagus sylvatica, Fraxinus excelsior, Populus tremula,
Prunus avium, Prunus padus, Tilia platyphyllos.
Known distribution: Europe (France, Italy, Switzerland, UK) and
Specimens examined: FRANCE: Ariège (09):
Rimont, Las Muros, ruisseau de Peyrau, 23 Apr. 1997, JF-97044, on
Fraxinus excelsior; Rimont, Las Muros, ruisseau de Peyrau, 21
Mar. 1998, 98036, on Corylus avellana; Rimont, Las Muros,
ruisseau de Peyrau, 25 Nov. 1998, JF-98179, on Corylus
avellana; Rimont, Grand Bois, 26 Feb. 1999,JF-99027, on Fagus
sylvatica; Rimont, Las Muros, 31 May 1999, JF-99106, on
Prunus avium; Rimont, Las Muros, 11 Sept. 2000, JF-00201, on
Rimont, Las Muros, ruisseau de Peyrau, 13 Jun. 2002, JF-02105, on Prunus
avium. Aude (11): Belcaire, Bois du Pinet,
1000m, 28 Sept. 2003, JF-03178, on Prunus padus. Pyrénées Atlantiques (64):
Oloron Ste Marie, Bois de Larbaig, 23 Aug. 1998, FC-603, on Fagus
Notes: Hypoxylon rutilum is a rarely recorded species, owing to its
discrete orange brown stromata easily confused with those of
H. perforatum and
It is distinctive in having minutely papillate
ostioles and red granules beneath the stromatal surface. Moreover, its
field identification is possible thanks to the characteristic sweetish
smell of the underlying wood of fresh specimens; unfortunately this smell
vanishes in herbarium material.
Ju and Rogers (1996) already noticed this
smell when culturing H. rutilum on Oatmeal agar and described it as
reminiscent of coconut oil.
It is also noteworthy that pulvinate stromata are usually composed of
several stromatal layers, each one growing year after year on top of the
other. This feature is also reported by
Mathiassen (1989) for
H. macrosporum on Salix bark,
and occasionally encountered in
some other taxa of Hypoxylon
In the field, H. rutilum may also be easily confused with the
rarely recorded H.
julianii which has similar stromata with ostioles opening
sometimes higher than the stromatal surface, similar small perithecia and
similar red granules under the stromatal surface.
differs in having much larger ascospores (15-18 x 6-7.5
µm) and in lacking specific smell. A possible confusion also exists with
H. laschii, which differs in having larger perithecia,
thicker basal tissue under the perithecia and lacks specific
As inferred from HPLC profiling
(Hellwig et al., 2002;
Stadler et al., 2004b),
H. rutilum belongs to the rubiginosum chemotype with mitorubrin
as prevailing compound, with rubiginosin A and orsellinic acid. Apart from the
lack of rubiginosin C, HPLC profile of H. rutilum appears almost identical
to that of
Moreover, these two taxa share a common unknown metabolite identified as Peak HR1
(Stadler et al., 2004b).
Our records on several different hosts show that H. rutilum is not restricted to
Fagus, and has a wider host range than previously assumed
Petrini & Müller 1986,
Ju & Rogers 1996).