The Pseudoperisporiaceae: Fungi on Leaves, Fungi on Fungi

Leaves of savin juniper Juniperus sabina, with fruiting bodies of the pseudoperisporiaceous fungus Chaetoscutula juniperi visible as black spots, from Tian et al. (2014). Scale bar = 1 mm.

As has been noted on this site before, the world of microscopic fungi includes a bewildering array of species that may never come to your attention but are in fact all around you. These organisms quietly live out their lives, often serving to break down the refuse that larger organisms such as plants shed over the course of their lives. Sometimes they are not so patient, instead attacking the plant while it is still green and growing. The subjects of today's post, the Pseudoperisporiaceae, include examples of both.

The Pseudoperisporiaceae are a widespread group of minute fungi that are most diverse in the tropical parts of the world. Because of their small size and lack (so far as is known) of significant economic effects, they are rarely noticed and little studied. However, they are by no means rare; in fact, one species in the family, Raciborskiomyces longisetosum, has been shown by molecular studies to be a major component of the soil community (e.g. Valinsky et al. 2002). The majority of members of the family grow on the leaves of plants, either as saprobes on leaf litter or as parasites on live plants. Alternatively, they may be parasites of other fungi, particularly sooty moulds. The more or less globular fruiting bodies (which are at most about 200 µm in size) are superficial on the surface of the host substrate, and are surrounded by a brown mycelium (mass of vegetative strands). Other distinctive features of the family include fusoid-ellipsoid ascospores (i.e. sexually produced reproductive spores) that are minutely warty and have rounded, subacute ends (Tian et al. 2014).

Closer view of fruiting body of Wentiomyces, from Wilk et al. (2014). Note the ostiole towards the lower left, surrounded by bilobed setae. Scale bar = 20 µm.

Pseudoperisporiaceae belong to the class of fungi known as the Dothideomycetes, a major subdivision of the Ascomycetes. Dothideomycetes include the majority of what used to be called the loculoascomycetes, so-called because of the way their fruiting bodies grow. A distinctive hollow, or locule, forms in the vegetative mycelium of the parent fungus, and the fruiting body develops within this hollow. In most Dothideomycetes (including the Pseudoperisporiaceae), the resulting fruiting body is almost entirely closed with a single opening (the ostiole) at the top through which the spores are released. Pseudoperisporiaceae also resemble other Dothideomycetes in having fissitunicate asci: that is, the asci (which are finger-shaped structures inside the fruiting body in which spores are formed) have a double-layered wall, with the outer layer being more rigid than the inner. As the inner layer swells with moisture, it causes the outer layer to split and the spores end up being expelled from the end of the ascus. Dothideomycetes are not the only fungi to show locular development, hence the dropping of loculoascomycetes as a formal group; the Chaetothyriomycetidae also grow their fruiting bodies from locules (Hyde et al. 2013).

The exact relationships of the Pseudoperisporiaceae with other Dothideomycetes remain uncertain; in their review of dothideomycete families, Hyde et al. (2013) left Pseudoperisporiaceae unassigned to an order within the class. Indeed, it is unclear to what extent Pseudoperisporiaceae are even related to themselves. Few members of the family have been studied from a molecular perspective, and those few that have been have not come out in the same place in the dothideomycete family tree. At least one supposed member of the family, the genus Epibryon, turns out not to even be a dothideomycete but is instead a chaetothyriomycete (Stenroos et al. 2010). Not for the first time on this site, I find that a seemingly simple outer morphology may be disguising a much greater diversity.

REFERENCES

Hyde, K. D., E. B. G. Jones, J.-K. Liu, H. Ariyawansa, E. Boehm, S. Boonmee, U. Braun, P. Chomnunti, P. W. Crous, D.-Q. Dai, P. Diederich, A. Dissanayake, M. Doilom, F. Doveri, S. Hongsanan, R. Jayawardena, J. D. Lawrey, Y.-M. Li, Y.-X. Liu, R. Lücking, J. Monkai, L. Muggia, M. P. Nelsen, K.-L. Pang, R. Phookamsak, I. C. Senanayake, C. A. Shearer, S. Suetrong, K. Tanaka, K. M. Thambugala, N. N. Wijayawardene, S. Wikee, H.-X. Wu, Y. Zhang, B. Aguirre-Hudson, S. A. Alias, A. Aptroot, A. H. Bahkali, J. L. Bezerra, D. J. Bhat, E. Camporesi, E. Chukeatirote, C. Gueidan, D. L. Hawksworth, K. Hirayama, S. De Hoog, J.-C. Kang, K. Knudsen, W.-J. Li, X.-H. Li, Z.-Y. Liu, A. Mapook, E. H. C. McKenzie, A. N. Miller, P. E. Mortimer, A. J. L. Phillips, H. A. Raja, C. Scheuer, F. Schumm, J. E. Taylor, Q. Tian, S. Tibpromma, D. N. Wanasinghe, Y. Wang, J.-C. Xu, S. Yacharoen, J.-Y. Yan & M. Zhang. 2013. Families of Dothideomyctes. Fungal Diversity 63: 1–313.

Stenroos, S., T. Laukka, S. Huhtinen, P. Döbbeler, L. Myllys, K. Syrjänen & Jaakko Hyvönen. 2010. Multiple origins of symbioses between ascomycetes and bryophytes suggested by a five-gene phylogeny. Cladistics 26: 281–300.

Tian, Q., P. Chomnunti, J. D. Bhat, S. A. Alias, P. E. Mortimer & K. D. Hyde. 2014. Towards a natural classification of Dothideomycetes 5: The genera Ascostratum, Chaetoscutula, Ceratocarpia, Cystocoleus, and Colensoniella (Dothideomycetes incertae sedis). Phytotaxa 176 (1): 42–54.

Valinsky, L., G. Della Vedova, T. Jiang, & J. Borneman. 2002. Oligonucleotide fingerprinting of rRNA genes for analysis of fungal community composition. Applied and Environmental Microbiology 68 (12): 5999–6004.

Wilk, M., J. Pawłowska & M. Wrzosek. 2014. Wentiomyces sp. from plant litter on poor fen in northeastern Poland. Acta Mycologica 49 (2): 237–247.