A New Concept on a Decomposing Log

Multiclavula mucidaa basidiolichen, on a wet and decomposing balsam fir log.
Multiclavula mucida, a Basidiolichen, on a wet and decomposing balsam fir log.

 

Documenting Local Biodiversity: Multiclavula mucida, a Basidiolichen

Introduction

This post is about a small lichen I found on my property in the spring of 2014. It is called Multiclavula mucida and is an unusual type of lichen. Although it is a widespread species in North America this lichen is easily overlooked. In fact, there are no records of it in the lichen herbarium collections for the state of Minnesota and only one for the related M. vernalis. So now, after a year of doing literature searches and also after finding more of these lichens in my woods I feel it is time to publish.

First Encounter

There were so many tiny plants and fungi sprouting in the forest last year after the long cold winter of 2013/2014. It was a wonderful sight and so much of it happened within in two weeks of the last snowfall in April. The odd fungal growth shown in the above photograph was found in the early spring of 2014 in my woods on a wet and decomposing balsam fir log. The tiny, pale club-like sprouts coming from this downed log are the fruiting bodies of a fungus that resembles coral mushrooms (Clavulina and Clavicorona) but are much smaller. The green film on the log is a green algae. The two organisms are growing together on the same substrate but the nature of the association is not immediately apparent.

 

Clavulicorna pyxidata, a coral fungus
Clavicorona pyxidata, a coral fungus related to Multiclavula mucida. Both are in the family Cantharellales but C. pyxidata is a saprophyte.

 

Lichens, Basidiolichens and Ectomycorrhizal Fungi

Lichens are technically defined as organisms that arise when two or more separate organisms (a fungus and green algae or a cyanobacteria or both) become physically and physiologically united into a single form. The fungal hyphae encloses the photosynthetic symbionts and the combined organisms form a new shape, develop new physical functions and biochemistry that is unlike those found when the organisms grow separately. They are then said to be “lichenized”.

During those cold winter nights of 2013/2014  I had been reading about an unusual type of fungus-algae association called “Basidiolichens”. The growth on the balsam fir log resembled the Basidiolichens Multiclavula mucida and M. vernalis I had read about. Basidiolichens are a lichen-like association between an algae (or sometimes a cyanobacteria) and a fungus in the phylum Basidiomyceta which includes many familiar mushrooms such as Pleurotus and Agaricus, two edible mushrooms often sold in grocery stores. Three genera of Basidiolichens are reported from North America although this association is known from all continents except (so far) Antarctica. Basidiolichens status as real lichens is debated and not all lichenologists will include them as lichens. They lack a lichenized thallus, one that is not divided into cortical and medullary layers which enclose the photobionts. But Basidiolichens represent a different type of fungus/photobiont symbiosis which the traditional concept of lichen cannot adequately encompass.

In Basidiolichens a fungus and an algae are growing in close association. Is this a lichen or just a mushroom just that happens to be growing with an algae? The lichenized form, at least when compared to a lichen such as Lobaria, is not very obvious. The fungus and the algae appear to be very distinct. A kind of thallus is present but it is not a “lichen thallus” with various layers of cortex and medulla. The powdery vegetative reproductive structures (isidia or soredia) known from Ascomyceta lichens are not present. The odd fungus and algae together on the log now look more like an accidental association, a facultative rahter than an obligate association.

But is it facultative? All species of Multiclavula known only occur in association with the algae Coccomyxa. (Votik 2006) According to Voitk and Esteri (2011) what is happening is that the Multiclavula is not growing from the wood like a decomposer with the algae just being there coincidentally. Instead, it has formed a kind of ectomycorrhizal association with the Coccomyxa. The cells of the algae are enclosed in a manner similar to what occurs when an ectomycorrhizal fungus encloses the root tips of live trees in the forest. In this case though it is not root tips or root hairs that are enclosed but single-celled algae. Like the ectomycorrhizal fungi that associate with trees the Multiclavula and the Coccomyxa are in a mutually beneficial relationship. Interestingly, recent genetic research has shown Multiclavula belongs with the family Cantharellales many of which are well-known ectomycorrhizal fungi (Nelsen et al. 2007).

 

Chanterelles
This mushroom (Cantharellus sp.) from the family Cantharellales is ectomychorrhizal.

 

Species of Coccomyxa are photobionts not only with the fungus Multiclavula but with another basidiolichen fungus Omphalina and “real” lichens such as Solonia and Peltigera. Also, Coccomyxa and its relative Pseudococcomyxa are reported to be symbionts with Paramecium and some other ciliate protists. Those that form associations with protists appear to be able to live freely as well.

Some members of the Cantharellales like Multiclavula have extended the ectomycorrhizal propensity of the family to include single-celled photosynthetic organisms. When understood in this way all plant-fungi associations where the fungus gets its carbon-based nutrients from the products of the photobiont as opposed to decomposition are “lichens”. Included in this would be parasitic fungi which would be a subdivision of lichens not a separate category. The question, Voitk and Esteri (2011) say, as to “how much fungal tissue around algae, the shape of the ‘thallus’ or the degree of algal incorporation is needed to be called a lichen becomes somewhat moot. The mighty Quercus and the lowly Coccomyxa become equals, different expressions of a diverse fungal photobiontism, and envelopment, ectomycorrhiza and arbuscular mycorrhiza become but examples of mechanics.”

The combined Multiclavula and Coccomyxa are known as Multiclavula mucida (lichen genera are always named after the fungal partner). Because the fungus Multiclavula is a Basidiomycota the lichen Multiclavula mucida is sometimes called a Basidiolichen. This group of lichens is composed of a few other genera, none closely related. It is a rather small group and most species are found in tropical regions although some species are from the temperate zone and even the Arctic. The species M. mucida is cosmopolitan in its distribution. The vast majority of lichens are associations with members of the fungus phylum Ascomycota or sac fungi with a green algae and/or cyanobacteria. Here in Basidiomycota like M. mucida we see a parallel evolutionary development similar in many respects to what is seen in Ascomycota, algae, and cyanobacteria symbiosis.

 

Multiclavula mucida
Multiclavula mucida

 

Description

M. mucida is easily recognized when the fungal fruiting bodies appear. These are about 1 to 5 mm tall, their caps pale yellow, sometimes pink tinged. The stem with the cap is spindle-shaped, the body of the stem is white with a few branches or none and often bent. Habitat for M. mucida is moist mixed conifer-hardwood or hardwood forests where it grows on moist decomposing logs either hardwood or conifer. Fruiting season is from late spring to fall. The 5-7 x 2.5-3 µm spores are ellipsoid. I have observed that the fruiting bodies persist over the winter into the following spring as does the algal thallus.

Significance

This appears to be the second record of M. mucida from Minnesota although I am only basing this on the records from the checklist of Minnesota lichens, the Keys to the Lichens of Minnesota, which was last updated in 2005, and a specimen record from Lake County in 1988 (Bessette 618532 at MIN). M. mucida was only recently reported from Michigan (Nelson 2005, Nelson 2007) and Wisconsin in 2006 (Bennett 000844 at WIS) from Vilas County.

Why there are so few records for M. mucida, a species with cosmopolitan distribution, from these three states is puzzling.

References Cited and Consulted

Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, CT.

Tedersoo, L., May, T. W., and  Smith, M. E. (2010). Ectomycorrhizal lifestyle in fungi: global diversity, distribution, and evolution of phylogenetic lineages. Mycorrhiza, Volume 20:217–263.

Hosina, R. and Inamura, N. (2008). Multiple origins of the symbioses in Paramecium bursaria. Protist, Volume 159(1):53-63.

LICHENISED BASIDIOMYCETES (Basidiolichens or Mushroom Lichens). Sydney Fungal Studies Group, Inc.

Nelsen, M. P. (2005). The basidiolichen Multiclavula mucida (Fr.) Petersen: new to Michigan. The Michigan Botanist 44: 192–193.

Nelsen, M. P., Lücking, R., Umaña, L., Trest, M. T., Will-Wolf, S. Chaves, J. L., and Gargas, A. (2007). Multiclavula ichthyiformis (Fungi: Basidiomycota: Cantharellales: Clavulinaceae), a remarkable new basidiolichen from Costa Rica. Amercan Journal of Botany, Volume 94(8):1289-96.

Nelsen, M. P. (2007). Noteworthy Collection: Multiclavula vernalis (Schw.) Petersen (Clavulinaceae). The Michigan Botanist 46: 124–126.

Pevelin, E. and Galun, M. (1976). Electron-microscopical Studies on the Phycobiont Coccomyxa Schmidle. The New Phytologist, Volume 77 (3):713-718.

Tibell, L. (1998). Practice and Prejudice in Lichen Classification. Lichenologist, Volume 30 (4-5):439–453.

Voitik, A. (2006). Three Lichenomphalias from the Top of Gros Morne Mountain. The Mycophile, Volume 47.

Voitk, A. and E. Ohenoja (2011). Genus Multiclavula in Newfoundland and Labrador. Fungi, Volume 4.

Ways of Enlichenment- Multiclavula

Wetmore, C. (2005). Keys to the Lichens of Minnesota. Department of Plant Biology, University of Minnesota.