Pleosporales - CBS - KNAW

Fungal Diversity
Fig. 53 Macroventuria wenti.
a Ascomata. Note the setae. b
Ascus and ascospores. Scale
bars: a=50 μm, b=10 μm
(figures referred to van der Aa
1971)
Following description is adapted from Hyde et al.
1996a, b).
Ascomata 455–650 μm high×980–1430 μm diam.,
scattered or in small groups, superficial, conical, carbonaceous,
papillate, under pseudostroma which forms a thin
layer on the host surface, up to 50 μm thick between the
ascomata and 125–250 μm thick on the ascomata surface
(Fig. 54a and b). Peridium 10–25 μm thick, comprising
several layers of compressed, densely packed, thin-walled,
hyaline cells. A wedge-shaped area of vertically orientated
hyaline palisade-like cells occurs at the periphery
(Fig. 54b). Hamathecium of dense, trabeculate pseudoparaphyses,
ca. 1μm broad, hyaline, branching and anastomosing,
septate, embedded in mucilage (Fig. 54e). Two
types of asci and ascospores exist in the same ascoma:
TYPE 1: asci 185–320×40–100 μm (x ¼ 210 78mm, n=
50), 8-spored, cylindro-clavate, bitunicate, fissitunicate,
short-pedicellate, with an ocular chamber (to 13 μm
wide×5 μm high) (Fig. 54c and d). Ascospores 66–84×
20–38 μm (x ¼ 78 25mm, n=50), 2-4-seriate, hyaline,
ellipsoidal, constricted at the central septum, with pad-like
mucilaginous appendage at each end and with some
mucilage associated around the spore, and TYPE 2: asci
158–242×8–15 μm (x ¼ 182 11mm, n=50), 8-spored,
cylindrical, bitunicate, fissitunicate, pedicellate, with an
ocular chamber and faint apical ring, ascospores 29–42×
6–9 μm (x ¼ 35 7mm, n =50), 1-2-seriate, brown,
ellipsoidal-fusoid, surrounded by a thin mucilaginous
sheath (Fig. 54f, g, h, i and j).
Anamorph: none reported.
Material examined: BRUNEI, on submerged wood,
Aug. 1997, leg. K.D. Hyde (HKU(M) 7425).
Notes
Morphology
Mamillisphaeria was established as a monotypic genus
according to its bitunicate, fissitunicate asci, trabeculate
pseudoparaphyses and dimorphic ascospores, which is
typified by the widely distributed freshwater fungus, M.
dimorphospora (Hyde et al. 1996a, b). The most striking
character of this fungus is its dimorphic ascospores, i.e.
one type is large and hyaline, and the other is comparatively
smaller and brown. Only a few ascomycetes have
been reported having dimorphic ascospores, such as
Aquasphaeria dimorphospora and Nectria heterospora
Speg. (Hyde 1995b; Spegazzini 1889). Dimorphic ascospores
appear to have evolutionary benefits, for example
the large ascospores with mucilaginous sheaths may
facilitate nutrient storage for germination and enhanced
collision and attachment to substrates. The smaller brown
ascospores may help resist desiccation and damage by UV
light and contribute to aerial dispersal, which might
explain the worldwide distribution of M. dimorphospora
(Hyde et al. 1996a, b).
Phylogenetic study
None.
Concluding remarks
Although in the key by Barr (1990a), M. dimorphospora
can be referred to Massariaceae, itistemporarily
assigned to Melanommataceae here based on its
trabeculate pseudoparaphyses embedded in mucilage
(Hyde et al. 1996a, b).