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The genus Ostreola Darker Can. J. Bot. 41: 1383. 1963 by
E.W.A. Boehm
Barr (1975, 1990)
recognized two muriform genera within the Mytilinidiaceae, Ostreichnion and Ostreola. Darker (1963) established the
genus Ostreola for dictyospored forms that otherwise resembled species of Mytilinidion, but was differentiated from
Ostreichnion by Barr (1987, 1990) based on smaller ascospores. Barr (1990) recognized two species from North America, O.
consociata Darker and O. formosa (Cooke) Barr, the later common on conifers in western North America, with spores similar to those
Hysterographium mori (Schw.) Rehm. Tilak and Kale (1968) added another two species from India, interestingly from non-coniferous
substrates. Barr (1990): "Ascomata
superficial, scattered or gregarious, separate or occasionally two, three or four fused in radiating pattern, elongate, conchate,
medium sized; apex cristate, opening by longitudinal slit; surface black, shining, often striate; peridium carbonaceous, brittle,
composed of small thick-walled cells. Asci basal, cylindric. Trabeculae few in gel matrix. Ascospores yellowish brown to dark
brown, ellipsoid or somewhat obovoid, symmetric or becoming asymmetric, straight or inequilateral, several transversely septate,
one (two) longitudinal septa, constricted or not constricted at first-formed septum; wall thick, smooth; one globule per cell;
overlapping uniseriate in the ascus. Anamorphs coelomycetous (Aposphaeria- or Peyronelia-like). On wood & periderm
of gymnosperms. Type species: Ostreola consociata Darker. Darker (1963) erected Ostreola for species with muriform ascospores
that are otherwise similar to Mytilinidion. He described two species from Quebec, O. consociata on Picea with associated Peyronelia state, which resembled Mytilinidion
tortile,
& O. sessilis on Pinus, whose ascomata somewhat resembled those of M. acicola. Ostreola sessilis, according to the type collection
(DAOM 90258: Quebec, Ste. -Ceile de Masham, Gatineau Co., 11 Jun 1960, G.D. Darker), is not congeneric with O
consociata. The ascomata are shield shaped, in a blackish crust, not cristate, & the peridium is pseudoparenchymatous, not
blackened nor brittle. The fungus appears to be pleosporaceous, although its generic position is still problematic."
Key to species of Ostreola Darker
North American species (Barr 1990):
I. Base of ascoma footlike, immersed in substrate; ascospores 14 - 18 (-22)
x 5 - 7 μm → Ostreola consociata Darker
II.
Base of ascoma tapered or applanate on surface of substrate; ascospores wider, 15 - 21 x 6.5 - 9.5 μm → Ostreola
formosa
(Cooke) Barr
Key
to species recovered from India (Tilak & Kale, 1968):
I.
ascospores biseriate, obovate, transversely 3 - 7 sepate, slightly constricted in the middle, 24 - 30 x 8 - 9.6 μm muriform
with two to three longitudinal septa, dull yellow-brown with brown walls & septa → Ostreola indica Tilak & Kale
II. ascospores irregularly biseriate obovate, transversely 3 - 6 septate,,
slightly constricted in the middle, 19 - 22.8 x 6 - 7.6 μm, muriform with 2 - 3 longitudinal septate, dull yellow-brown
with brown walls & septa → Ostreola zizyphii Tilak & Kale
Ostreola consociata Darker Daker, Canad. J. Bot. 41: 1384. 1963. Type: Picea glauca, Bic sur Mer, Rimoushi Co., Quebec, Canada, 12 Sep 1961, G.D. Darker 8065 DAOM 90254! (holotype). Barr (1990): "Ascomata 270 - 680 μm long, 200 - 380 um wide, 200 - 300 μm high, conchate, bases footlike
in substrate; peridium 25 - 35 (-50) um wide. Asci 95 - 130 x 9 - 11 um. Ascospores 14 - 18 (-22) x 5 - 7 μm, dull yellowish
brown, 3 - 5 (-7) septate, longitudinal septum in mid cells. Distribution: On periderm of Pinaceae, northeastern North America."
Ostreola formosa (Cooke) Barr Barr, Mycotaxon
29: 505. 1987. Hysterium formosum Cooke, Grevillea 7: 3. 1878 Hysterographium
formosum
(Cooke) Saccardo, Syll. Fung 2: 783. 1883. Hysterographium pumilionis Rehm in Rabenhorst, Kryptogamen-Flora 1(3): 21. 1887 Distribution: On gymnosperms, alpine regions, western North America, Europe.
Barr (1990): "Ascomata conchate, usually cristate, up to 500 μm long, 140 - 170 μm wide,
180 - 250 μm high; surface longitudinally striate; peridium 20 - 24 μm wide, blackish brown, brittle. Asci 83 - 130
x 9 - 14.5 μm. Ascospores 15 - 21 x 6.5 - 9.5 μm, light to dark brown, ellipsid, ends obtuse or somewhat acute, (3-)
5 (6-) septate, one & at times partially two longitudinal septa in mid cells, often constricted at first-formed septum.
(Material examined: Canada, British Columbia, Mimuls Lake, Garibaldi Prov. Park, 2 Aug 1952, M.E. Barr 615b; Black Tusk Lake,
6 Aug 1952, Barr 664b. Both on Abies amabilis, MASS; Mt. Paddo, Aug 1885, WA, USA, W.N. Suksdorf, NAF 2062 MASS). Notes:
This species, on conifers in alpine regions of western North America, has usually been included under Hysterographium
mori (Schweinitz)
Rehm. It differs from H. mori in habitat, ascomata, peridium & centrum, although the ascospores are quite similar in both
species. In culture the two differ both in colony characteristics & conidia (Lohman, 1933). Both form pycnidial conidiomata;
the conidiogeous cells of O. formosa are short ampullaceous & produce nearly globose conidia, whereas those of H.
mori
are narrowly elongate & produce oblong or obovoid conidia. Lohman observed that the conidiogenous cells & condia in
O. formosa were of the type described for Mytilinidion tortile."
Two additional species described from India by Tilak & Kale (1968). Note: Most mytilinidiaceous fungi have been
recovered from gymnosperms, with the exception of the genus Ostreichnion, now transferred to the Hysteriaceae
(Boehm
et al. 2009). These two species of Ostreola are also an exception.
Ostreola indica Tilak & Kale Tilak S.T. & Kale S.B. Indian Phytopathology 21: 289. 1968.
Tilak
& Kale (1968): "Hysterothecia mostly crowded in scattered groups conchiform to hatchet-shaped, occasionally triradiated,
slightly crested fragile, opeining narrowly by a longitudinal slit, at maturity 1 - 1.5mm long shining black, umbonate, with
concentric striae, at base abruptly narrowing to a rounded or elliptical attachment with the substratum; hysterothecia in
transverse section 600 - 700 μm high, 500 - 550 μm broad, with covering layer of dark pseudoparenchyma in centre thick
with apex abruptly tapering to the more or less closed lips, brown basal pseudoparenchyma often continued int the substratum
as a foot-like structure, hypothecium of thin walled parenchymatous cells, hymenium flat; asci cylindrical, 152 - 171 x 13.3
- 15.2 μm bitunicate, octospored, pedicellate, paraphysate, paraphysis simple or branched, equaling or slightly longer
than the asci; ascospores biseriate, obovate, transversely 3 - 7 sepate, slightly constricted in the middle, 24 - 30 x 8 -
9.6 μm muriform with two to three longitudinal septa, dull yellow-brown with brown walls & septa. In culms of Madhuca
indica
Gmel et Manchappa, Nov 1967, S.B. Kale & S.G. Meddakker. Marathwada University, Aurangabad & Herbarium Cryptogamie
Indiae Orientalis, New Delhi, India: MUH 208".
Ostreola zizyphii Tilak & Kale Tilak S.T., & Kale S.B. Indian Phytopathology 21:
290. 1968.
Tilak & Kale (1968):
"Hysterothcia mostly crowded, in groups, conchiform to hatchet-shaped, occasionally tri-radiate slightly crested fragile,
opeingin narrowly by a longitudinal slit, at maturity 2 - 3mm long, shining black, umbonate, with concentric striae, at base
abruptly narrowing to a rounded or elliptical attachment with the substratum; hysterothecia in transverse section 300 - 450
μm high, 195 - 225 μm broad with covering layer of dark pseudoparenchyma in the center thick with apex abruptly tapering
to the more or less closed lips, brown basal pseudoparenchyma often continued into the substratum as a foot like structure,
hypothecium of thin walled parenchymatous cells, hymenium flat; asci clavate to cylindrical 57 - 67 x 15.5 - 19 μm bitunicate,
octospored, paraphysate, paraphysis simple or branched, equaling or slightly longer than the asci; ascospores irregularly
biseriate obovate, transversely 3 - 6 septate,, slightly constricted in the middle, 19 - 22.8 x 6 - 7.6 μm, muriform with
2 - 3 longitudinal septate, dull yellow-brown with brown walls & septa. In culms of Zizyphus jujuba Lam et Awarad Nov 1967 Marathwada
University, Aurangabad & Herbarium Cryptogamie Indiae Orientalis, New Delhi, India: MUH209".
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