Pleosporales - CBS - KNAW

Fungal Diversity
≡ Sphaeria nucula Fr., Syst. mycol. (Lundae) 2: 466 (1823).
Ascomata 200–240 μm high×200–280 μm diam., scattered,
erumpent to nearly superficial, with basal wall remaining
immersed in host tissue, globose to subglobose, often
laterally flattened, with a flattened base not easily removed
from the substrate, black, roughened; with a cylindrical or
slightly compressed papilla. Papilla to 120 μm long and
150 μm high, protruding, with a pore-like ostiole (Fig. 52a).
Peridium 25–30 μm wide, very thin at the base, composed of
heavily pigmented pseudoparenchymatous cells near the apex,
cells 2–2×6 μm diam., wall 1–3(−4) μm thick, lower sides
composed of pigmented cells of textura angularis, 3–5 μm
diam., wall 0.8–1.5 μm thick, ostiole wall composed of
heavily pigmented and thick-walled small cells (Fig. 52b and
c). Hamathecium of dense, long, septate pseudoparaphyses,
1–2 μm broad, anastomosing and branching between and
above asci, embedded in mucilage (Fig. 52i). Asci 90–115×
9–11.5 μm (x ¼ 99:5 11:5mm; n=10), 8-spored, bitunicate,
fissitunicate, cylindrical, with a short, narrowed, furcate
pedicel which is up to 10 μm long, with a small ocular
chamber (ca. 1.5μm wide×1 μm high) (J-) (Fig. 52d, e, f
and h). Ascospores 17–21(−25)×(4-)5–6.5 μm
(x ¼ 19:5 5:5mm, n=10), obliquely uniseriate and partially
overlapping to biseriate, broadly fusoid to fusoid, with
narrowly rounded ends, hyaline and lightly pigmented on
very rare occasions when senescent, 1-septate, 3-septate
when old, constricted at the median septum, the upper cell
often broader than the lower one (Fig. 52g).
Anamorph: none reported.
Material examined: on decaying wood (UPS, lectotype
as Sphaeria nucula Fr.).
Notes
Morphology
Holm and Holm (1988) provided a relatively strict
definition for Lophiotrema after they examined several specimens
including the type materialwhichtheylectotypified.
Lophiotrema was mainly defined on the unique characters of
small to medium ascomata, a “Lophiotrema-type” peridium
and 1-septate ascospores. In Lophiotrema, Holm and Holm
(1988) considered the ascomata to be small- to medium-sized,
ca. pyriform but neck often reduced, even lacking and
sometimes cylindrical. The peridium was of approximately
equal thickness, 20–30 μm, composed of an outer textura
angularis of uniformly pigmented cells, up to 12 μm, andan
inner layer of very small hyaline cells, with somewhat
thickened walls. Asci are cylindrical, spores hyaline, at first
1-septate, becoming 3-septate, with distinct guttules, often
with a mucilaginous sheath. Much emphasis was given to the
1-septate ascospores by Holm and Holm (1988) when they
described and distinguished the three Lophiotrema species: L.
boreale, L. nucula, L. vagabundum (Sacc.) Sacc. and two
Fig. 51 Lophiostoma macrostomum (a–h, j from UPS, leptotype; i b
from IFRD 2005). a Appearance of ascomata on the host surface.
Note the raised crest-like areas and full length germ slits. b Section of
the peridium. c–e Cylindro-clavate asci with ascospores arranged in a
2-3-seriate manner. f Hamathecium comprising branching and septate
pseudoparaphyses. g–j Released or unreleased ascospores. Note the
smooth young ascospores with terminal sheath, and the verrucose
senescent ascospores. Scale bars: a=0.5 mm, b=200 μm, c–j=10 μm
other unnamed species. This concept was widely accepted by
later workers (Kirk et al. 2001; YuanandZhao1994). Tanaka
and Harada (2003c) considered the peridium and asci to
distinguish Lophiotrema from Lophiostoma, while Tang et al.
(2003) introduced a new Lophiotrema species with elongated
slit-like ostiole stating that the main difference between
Lophiotrema and Lophiostoma were size of ascomata,
structure of peridium, shape of asci and sheath of ascospores.
This peridium concept however, is not supported by the
lectotype specimen we examined here, which has a flattened
thin-walled base. Thus the “Lophiotrema-like peridium” sensu
Holm and Holm (1988) should not serve as a diagnostic
character of Lophiotrema, while the ostiole, asci and
ascospores might have some phylogenetic significance (Zhang
et al. 2009b). No anamorph is yet known for Lophiotrema.
Although the ascospores was reported by Holm and Holm
(1988) to be verruculose this could not be observed in the
lectotype examined under light microscope (1000 ×) in the
present study.
Phylogenetic study
In the phylogenetic study of Lophiostoma, Massarina and
related genera (Zhang et al. 2009b), Lophiotrema nucula
formed a consistent and robust clade with three other
Lophiotrema species: L. lignicola Yin. Zhang, J. Fourn. &
K.D. Hyde, L. brunneosporum Yin. Zhang, J. Fourn. & K.D.
Hyde and L. vagabundum, separate from other members of
Lophiostoma and Massarina sensu stricto. This clade might
represent Lophiotrema sensu stricto, however, the correctness
of strains of L. vagabundum (CBS 628.86) and L.
nucula (CBS 627.86) used in the phylogenetic study are not
verified and warrant further study.
Concluding remarks
Holm and Holm (1988) distinguished Lophiostoma from
Lophiotrema based on the smaller ascomata, 1-septate
versus multi-septate ascospores, and peridial wall structure.
However, we doubt that these distinguishing characters
(size of ascomata, number of septa of ascospores) can be
confidently used to separate these genera and we could not
establish any characters that could reliably distinguish
between these two genera. The molecular data, however,
does separate Lophiostoma macrostomum and Lophiotrema
nucula into separate clades and provides some support that
these are separate genera. Although the strain of L. nucula