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):
- Base of ascoma footlike, immersed in substrate; ascospores 14 – 18 (-22) x 5 – 7 μm →Ostreola consociataDarker
- 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):
- 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 indicaTilak & Kale
- 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″.