The genus Ostreichnion Duby
Duby, Mem. Soc. Phys. Hist. Nat. Geneve 16: 22 (1862)
by Eric W.A. Boehm
Ostreion Saccardo, 1883
Duby (1862) established the genus Ostreichnion Duby for O. europaeum Duby and O. americanum Duby, with an etymology from Ostrea, a genus of oysters. Saccardo (1883; p. 765) considered the name Ostreichnion to be linguistically incorrect and substituted Ostreion Duby, a situation later rectified by Barr (1975). In studying Duby’s specimen of O. europaeum, Rehm (1886) considered the species to be a pedicellate form of Hysterium pulicare, leaving only the type species, O. americanum, which was later consigned to the earlier name O. sassafras (Schw.) M.E. Barr (Barr 1975). O. sassafras occurs on both sides of the Atlantic, as well as in China, and has been recovered from Sassafras, Quercus, Liriodendron, and Liquidambar (Barr 1975; Bisby 1932; Teng 1933). Some confusion has existed as to the nature of spore septation in O. sassafras. Most authors regarded the ascospores as multiseptate and Saccardo (1883) classified Ostreichnion (as Ostreion) in the Phaeophragmiae. When longitudinal septa were observed they were regarded as pseudosepta (Bisby 1932). This eventually led Zogg (1962) to include Ostreichnion (as Ostreion) under the genus Mytilinidion. However, Massee (1895) had earlier noted and illustrated large muriform ascospores for both American and British specimens. Barr (1975) thus maintained Ostreichnion as a separate genus in the Mytilinidiaceae because of the muriform nature of the large ascospores, usually borne four to an ascus.
Barr (1975) also transferred two additional species to the genus Ostreichnion. Hysterium nova-caesariense Ellis was removed from synonymy with Hysterographium flexuosum (Zogg 1962) and accepted as O. nova-caesariense (Ellis) M.E. Barr, known only from the type locality in New Jersey on Pinus, and having similar, but smaller, muriform ascospores as O. sassafras (Barr 1975). The second species accepted in the genus was O. curtisii (Duby) M.E. Barr, derived from Glonium curtisii (Duby) Lohman, an unusual fungus from the Coastal Plain and the southeastern United States to Louisiana (Lohman 1937) and also reported from Brazil (Zogg 1962). Barr (1975) made the transfer from Glonium in the Hysteriaceae to Ostreichnion in the Mytilinidiaceae, based on the broadly conchate ascocarps with a brittle, thin-walled prosenchymatous peridium enclosing a centrum similar to that found in O. sassafras, that is containing trabeculae in a gel matrix. However, O. curtisii possesses highly unusual ascospores that bear little resemblance to the muriform ascospores found in the previous two species (Barr 1975; Lohman 1937). In O. curtisii, the ascospores are one-septate below the middle, with walls greatly thickened towards the spore apex. Under different stains, the spore cytoplasm is clearly subdivided into numerous compartments, giving the impression of potentially muriform ascospores. Lohman (1937) provided details as to the highly unusual spore germination process in this fungus, which involves a distended apical plug and numerous median germ tubes, differing from that found in other species of Glonium that send out apical germ tubes (Lohman 1931, 1932a).
In a recent molecular phylogenetic study Boehm et al. (2009a), we were able to secure two cultures, originally deposited by Lohman in the 1930s, representing two of the three currently recognised species, namely O. sassafras (CBS 322.34) and O. curtisii (CBS 198.34) (Table 1, below). Phylogeny presented clearly indicates that the genus Ostreichnion, previously classified in the Mytilinidiaceae (Barr 1975), falls within the Hysteriaceae (Figs. 2 & 3, below). Furthermore, both species of Ostreichnion appear unrelated to each other. Given the unique nature of the ascospore of O. curtisii, considered potentially muriform, one would assume affinities with the genus Hysterographium, or, given its uniseptate ascospores at maturity, within the genus Glonium, where it was originally placed by Lohman (1937). However, molecular data indicate that O. curtisii, instead finds affinity with the clade containing the core group for the genus Hysterium, including H. pulicare, the type, and H. angustatum, surprisingly with strong support (Figs. 2 & 3). A phylogenetic affinity with the genus Hysterium was entirely unexpected. Conversely, the taxon O. sassafras, with large muriform pigmented ascospores, borne usually four to an ascus, belongs to the clade supporting Gloniopsis praelonga, although support is weak (Figs. 2 & 3). Based on the data presented (Boehm et al. 2009), the genus Ostreichnion was transferred from the Mytilinidiaceae to the Hysteriaceae. Data indicate that the two species surveyed (O. curtisii & O. sassafras) are unrelated and, thus, we recognize the genus as highly artificial. However, until more taxa are available it is premature to begin restructuring the genus Ostreichnion.
The inclusion of the genus Ostreichnion in the Hysteriaceae raises a number of important issues. Unlike the thick-walled hysterothecium, the ascocarp in Ostreichnion is thin-walled, conchate, and possesses trabeculate pseudoparaphyses (Barr 1975, 1990). Including the genus Ostreichnion in the Hysteriaceae (Figs. 2 & 3) implies that, either morphological features within the genus need to be re-evaluated, or that the family Hysteriaceae must also encompass some mytilinidioid forms. This may not be that surprising if we consider the reverse process. Earlier, in the case of Hg. fraxini / H. hyalinum and Gl. stellatum / Gl. circumserpens (see Gloniaceae), it was seen that the hysterothecium is not a synapomorphic trait uniting the Hysteriaceae, but rather it occurs in at least two groups outside of the family proper. Thus, one can presume that the reverse process, in which the evolution of thin-walled hysterothecia, approaching the conchate configurations seen in the Mytilinidiaceae, evolved within the Hysteriaceae, a convergence due perhaps to similar selective pressures.
Barr (1990): “Ascomata superficial, scattered or gregarious, bases sometimes immersed in substrate, conchate, medium to large sized; surface black, dull or shining, longitudinally striate at times; apex cristate, opening by longitudinal slit; peridium carbonaceous, brittle, composed of small heavily pigmented cells. Asci basal, clavate or cylindric. Trabeculae in gel matrix. Ascospores yellowish becoming reddish brown to dark brown, ellipsoid or nearly cylindric, ends obtuse or acute, symmetric or nearly so, straight or inequilateral, one- to several septate, usually one to three longitudinal septa, but these sometimes lacking constricted at first-formed septum; wall smooth or irregularly roughened; guttulate; overlapping biseriate in the ascus. Anamorphs not known. On woody angiosperms & gymnosperms. Type species: Ostreichnion americanum Duby = Ostreichnion sassafras (Schweinitz) Barr. Notes: The species have been dispersed in other genera, but Barr (1975) justified uniting them under Ostreichnion. The ascospores may show distosepta when young, & the ascus a suggestion of refractive ring around the wide ocular chamber. Such features are suggestive of the Massariaceae, but the shape of the ascomata & structure of the peridium dictate membership in the Mytilinidiaceae.”
Key to the species of Ostreichnion
- Ascospores mostly 1-septate, ends greatly thickened, (45-)62-80 x (10-)12-15 μm; North & South America → Ostreichnion curtisii (Duby) M.E. Barr
- Ascospores with both transverse and longitudinal septa → 2
- Ascospores measuring 35-45(-50) x 11-13 μm, with 7-13 septa, borne eight to an ascus; North America → Ostreichnion nova-caesariense (Ellis) M.E. Barr
- Ascospores measuring (65-)76-100(-135) x 20-32 μm, with up to 27 septa, borne four to an ascus; cosmopolitan → Ostreichnion sassafras(Schwein.) M.E. Barr
Ostreichnion curtisii (Duby) M.E.Barr
Barr, 1975, Mycotaxon 3: 86.
Hysterium curtisii Duby, 1862
Gloniella curtisii (Duby) Saccardo, 1883
Hysterographium curtisii (Duby) Earle, 1901
Glonium curtisii (Duby) Lohman, 1937
Hysterium cyrillae Berkeley & Curtis, 1875
Glonium cyrillae (Berkeley & Curtis) Saccardo, 1883
Psiloglonium cyrillae (Berkeley & Curtis) Muller, 1962
Hysterium chlorinum Berkeley & Curtis, 1875
Glonium chlorinum (Berkeley & Curtis) Saccardo, 1883
Glonium macrosporium Tracy & Earle, 1896
Glonium gigasporum Ellis & Everhart in Herb. Ellis, ined.
Barr (1990): ” Ascomata 1mm long or longer, 440 – 470 μm wide, 330 – 385 μm high; surface longitudinally striate, shining, at times powdered with greenish coating; peridium 52 – 65 μm wide, blackened & encrusted externally, yellowish internally. Asci 150 – 180 (-220) x 25 – 30 (-40) μm. Ascospores (45-) 62 – 82 x (10-) 12 – 15 (-17) μm, yellowish brown, one septate, potentially seven- or more septate, longitudinal septum in one or more cells. Distribution on woody branches, southeastern USA; reported from Brazil (Zogg, 1962). Alabama: Tuskegee, Macon Co., Jan 1900, on Vitis rotundifolia, G.W. Carver, F. Col. 1536 as Hysterographium viticolum (MASS); Florida: Green Cove Springs, Clay Co., Winter 1884, collected from Sabal, G.W. Martin, Ellis N.A.F., 1321 as Hysterium lineolatum (MASS). Louisiana: Delta Regional Primate Center, 5 June 1976, M.E. Barr 6324b (MASS). South Carolina: Quercus, H.W. Ravenel, F. Car. 48 as Hysterium flexuosum (MASS). Note: Lohman (1937) described & illustrated details of the species which is quite common in southeastern USA. His account & illustrations of ascospore germination are illuminating.”
Ostreichnion nova-caesariense (Ellis) M.E. Barr
Barr, 1975, Mycotaxon 3: 84.
Hysterium nova-caesariense Ellis, 1877
Mytilidion nova-caesariense (Ellis) Rehm, 1883
Hysterographium nova-caesariense (Ellis) Roumeguere, 1892
Barr (1990): “Ascomata up to 1mm long, 275 μm wide & high; surface faintly longitudinally striate; peridium 20 – 25 μm wide, blackish brown, brittle. Asci 100 – 130 x 30 – 40 μm. Ascospores 35 – 45 (-50) x 11 – 13 μm, dull brown, seven to thirteen septate, with one to three longitudinal septa. Distribution on periderm of Pinus rigida, known only from the type locality: USA New Jersey, Newfield, Gloucester Co., Apr. 1893, J.B. Ellis. Note: Zogg (1962) included this taxon as a synonym of Hysterographium flexuosum (Schweinitz) Saccardo, but the brittle peridium & trabeculae are quite different from the thick peridium & cellular pseudoparaphyses in Hysterographium as are the ascospore shapes.”
Ostreichnion sassafras (Schw.) M.E. Barr
Barr, 1975, Mycotaxon 3: 83.
Lophium sassafras Schweinitz, 1832
Mytilinidion sassafras (Schweinitz) Zogg
Ostreichnion americanum Duby, 1862
Ostreion americanum (Duby) Saccardo, 1883
Barr (1990): “Ascomata 1 – 1.5mm wide & high or up to 2mm high, about 750 μm wide in side view; peridium 26 – 40 μm wide at sides, 52 – 65 μm wide above, 104 – 115 μm wide at base. Asci 220 – 330 x 30 – 40 μm, usually only four spored. Ascospores (65-) 76 – 100 (-135) x 20 – 32 μm, yellowish to dark brown, end cells pallid, up to twenty seven septate with one to five longitudinal septa. Distribution on periderm or decorticated wood, southeastern USA; reported from China (Zogg, 1962 following Ten, 1933). Florida: Ocala, Marion Co., 1897 – 1898, R. Thaxter, Rel., Farlowianae 626 (NY). Georgia: Chattooga River, Rabun Co., 10 Mar 1934, Quercus, M.L. Lohman 583 (NY). North Carolina: South Toe River, Yancy Co., 30 Nov 1933, Quercus, M.L. Lohman 530; Old Fort, 22 May 1934, Liriodendron tulipifera, M.L. Lohman 579; Yadkinville, 12 Apr 1935, Quercus, M.L. Lohman 582 (all NY); South Carolina: Laurus, H.W. Ravenel (NY two collections); N. of Pickens, Pickens Col, 26 May 1934, Quercus, M.L. Lohman 580, 581 (all NY) – all listed as Ostreichnion americanum. Note: Zogg (1962) was unable to examine material & utilized earlier descriptions & opinions when he transferred the species to Mytilinidion. The ascospores of Ostreichnionsassafras are both notably larger & differently septate than in any species of Mytilinidion.”