Xylaria: What, where, how?

This post was originally published in The Journal of Wild Mushrooming, and is modified slightly for this format.


What: recognition and classification

Any avid mushroom hunter will likely have seen them, reaching blackly (and vaguely ominously) upward from twisted, rotting wood on the forest floor. Maybe you’ve ignored them—‘there’s no way that can be edible’, you might have said to yourself—or maybe you’ve pulled a few from the log they were growing on for closer examination later, noting their reluctance to separate from the decaying but surprisingly hard wood. They might have been hard, brittle, black, like charred twigs, or maybe they were a little cartilaginous, black below, but with pale, powdery tips, releasing a small puff of white, dusty spores to the air as you pulled them from their wooden home. Arora’s Mushrooms Demystified takes you to Xylaria hypoxylon (Fig. 1), the candlesnuff fungus (“much too tough to be of value”), or maybe Xylaria polymorpha, with the morbid sounding common name of dead man’s fingers (“much too tough and rough to be edible”). The notes here hint at a hidden diversity, but the descriptions in this and similar mushrooming guides leaves the reader wondering, holding a small, black fruiting body, with a name that may or may not be correct, and more questions than answers.

Xylaria hypoxylon

Xylaria hypoxylon, photo by Alan Rockefeller (MO 225661). This is a young fruiting body: note the pale surface at the upper end (from which it gets the name candlesnuff fungus) and the flattened branching tips, characteristic of this species and close relatives. Perithecia have not developed yet, but will swell from beneath the outer white coating, which will eventually slough off, leaving the black carbonized layer exposed.

The name Xylaria (say “Zai-LAIR-ee-ah”) slides off the tongue, sounding vaguely Germanic and vaguely Latin at the same time, hinting—at least for me—of exotic places and unimagined complexity. This impression is not far from the truth: there are over 400 species of Xylaria in the world, making it one of the largest genera of ascomycetes, and most of those species are tropical. What defines this enormous genus, and binds the complexity of tropical species with the more familiar Candlesnuff Fungus?

To work down from the top, so to speak, the first thing that must be recognized is that Xylaria are ascomycetes, not basidiomycetes like the gilled mushrooms. That puts Xylaria in the same broad group as morels—these are fungi with spores borne in little sacs called asci, which is why ascomycetes are often collectively called “sac fungi”. From the ascomycetes, there is a broad division between fungi that carry their asci on fertile surfaces, called an apothecia—such as the wrinkled surface of the morel—or inside of little enclosed, flask-like chambers, called perithecia, like Xylaria. Perithecial fungi are often called “flask fungi”, because of the shape of their spore-bearing parts. Hypomyces lactofluorum, the fungus responsible for turning Lactarius and Russula into delicious lobster mushrooms, is a flask fungus many people have likely encountered without knowing. When next you see a lobster mushroom, look closely at the surface, and you will see the little orange perithecia embedded in the tissue of the host Russula mushroom: one fungus eating another, subverting the fruiting body of its host to make its own fruiting bodies.

Within the flask fungi, Xylaria are the namesake for their family (the next organizational step up from genus), the Xylariaceae. This family is set apart from other families of flask fungi by many things, but the most noticeable is the generally “carbonaceous” texture of the fruiting bodies. Fungi in this family are nearly all coated in a blackened, hard, brittle layer, like charcoal. Additionally, most fungi in the Xylariaceae have eight darkly-coloured, single-celled spores in each ascus. Lastly, to distinguish Xylaria from the other genera in the family, you generally only have to look for the rising fingers of the fruiting body: nearly all of the other members of the family lay flat against their substrate. Not that there aren’t any other upright fungi in the family, but these are usually growing on something other than wood—most often the fibrous dung of herbivores—and generally have a paler surface, and a more stem-and-cap-like shape (such as Podosordaria or Poronia). So, how do you know a Xylaria when you see one? Generally (for there are always exceptions), by its black, hard, upright fruiting body with embedded perithecia growing on wood.

Xylaria globosa

Xylaria globosa, the Rubied Xylaria, photo by Danny Newman. This is a young fruiting body: note droplets of bright red exudates. At maturity, there are no red droplets, and as in Xylaria hypoxylon, the pale outer surface layer is shed to expose the black, carbonized surface, with the perithecia embedded within.

Where: diversity, at home and away

Holding a Xylaria in your hand, it is obvious that you cannot eat it. Xylaria are not interesting because they are good to eat, they are interesting because they are likely major players in the Earth’s breathing: the global carbon cycle. In the tropics, Xylaria are some of the most common wood decay fungi encountered, and while estimates vary, it is certain that they are responsible for a great deal of conversion of fixed carbon in wood back into carbon dioxide in the atmosphere—the slow exhaling of the Earth. They are also interesting because of the diversity of secondary chemicals they produce. The diversity of strange chemistry in these fungi has been recognized for some time, and there is great interest in exploring for medicinal benefit. One species, Xylaria nigripes—part of a subgroup of Xylaria that grow specifically from the nests of termites—is used in traditional Chinese medicine to treat sleep disorders. Lastly, they are interesting because they represent a significant pool of unexplored fungal diversity.

The diversity of Xylaria in the world is staggering. It is the largest genus in one of the largest families of ascomycetes, which in turn is the largest division of fungi. There are, on last count, more than 800 named species of Xylaria in the world. However, according to world experts (and my own experience), it is likely that only about half of these names represent “good” species, meaning many names are duplicates, where two people have described and named the same fungus, unaware of the each other’s work. Sadly, there is currently no single reference for the genus Xylaria; the group has never been monographed, despite hundreds of years of study. This is due, in part, to the complexity and enormity of the task, and, more recently, to a lack of financial support for taxonomic science (the classification of organisms) from federal funding agencies.

Luckily, such support was not always lacking. There exists an excellent series of papers from the inestimable Dr. Jack D. Rogers—a boisterous, fast-talking, old West Virginian, transplanted to Washington State many years ago—on the classification of the Xylaria from the continental United States, including an excellent key to species (see list of further reading, below). He lists more than two-dozen common species in the US, and suggests that there may be many more rare species. The commonly encountered species include the Candlesnuff Fungus and dead man’s fingers, but also many other species. These include Xylaria apiculata, often confused for Xylaria hypoxylon, but with small, pointed apices to the fruiting bodies, and spores with a shorter germ slip, and Xylaria magnoliae, which is similar to Xylaria hypoxylon but grows exclusively on the old fruits of magnolia trees in the southeast of the United States. There is also an excellent work from Jack’s lab, made in cooperation with the Illinois Natural History Survey and the Russian Academy of Sciences, on the Xylaria and related fungi of the Great Smoky Mountains National Park, which has some of the highest Xylaria diversity in North America.

In the tropics, the diversity increases exponentially, with some locations—like my field site is the cloud forests of Ecuador—having fifty or more species! In addition to there simply being more species around, there also seems to be greater variance within species, which makes accurate identification particularly difficult. To identify tropical American Xylaria, the first place to look is an old paper from R.W.G. Dennis from 1956 called “Some Xylarias of Tropical America”. From there the hunt for a species identity becomes a bit of a scientific “where’s Waldo” through the taxonomic literature. There have been some wonderful pieces in recent years that will help the curious mycophile identify tropical American Xylaria, like Hladki and Romero’s account of Xylaria from the Tucuman province of Argentina, or Felipe San Martín González’s preliminary account of Xylaria from Mexico.

Despite the difficulty in identification, there are some amazing species in the tropics. Xylaria globosa, the Rubied Xylaria (Fig. 2), exudes droplets of bright red fluid early in its life, making young fruiting bodies appear to be studded with rubies. Xylaria tucumanensis (Fig. 3), one of a group of closely related, very slender Xylarias, is so slight it almost seems to be just perithecia attached to a central stalk. The closest tropical relative to the familiar dead man’s fingers is called Xylaria schweinitzii (Fig. 4), named after Lewis David von Schweinitz (1780–1834; often called the “Father of North American Mycology”) who first collected it. This species is more robust than Xylaria polymorpha and tends to have a smoother surface, as well as a diagonal germination slit on the ascospores in contrast to the straight slit of Xylaria polymorpha.

Xylaria tucumanensis, photo by Danny Newman. There are mature fruiting bodies of this tiny, elegant Xylaria: note the nearly naked perithecia on their central stalk, with the characteristic pointed apex at the tip. There is a group of young, immature fruiting bodies still coated in the pale conidial layer in the far right of the frame.

Xylaria tucumanensis, photo by Danny Newman. There are mature fruiting bodies of this tiny, elegant Xylaria: note the nearly naked perithecia on their central stalk, with the characteristic pointed apex at the tip. There is a group of young, immature fruiting bodies still coated in the pale conidial layer in the far right of the frame.

How: identification and why it’s important

To use any of the keys to identification listed in the Further Reading section, you will need a microscope. The key characters for identifying Xylaria include the size and shape of the ascospores, and the placement and length of the clear germination slit (germ slit for short) on one side of the spore. These characters are taxonomically stable, meaning that there may be great variance in other characters that do not indicate difference between species, but these characteristics are the same within a given species, and different between species. Also useful is the apical plug, a structure at the tip of the ascus that may serve as a pore through which the spores are squeezed out, or may be the point of rupture when the ascus is ready to break and release the spores. The apical plug stains bright blue in an iodine stain, like Melzer’s reagent, so slides are usually from perithecial contents, mounted in Melzer’s so that you can see it. See these structures illustrated with Xylaria schweinitzii in Figure 4.

This need for microscopic characteristics is one of the great hurdles to amateur collection and contribution to knowledge of Xylaria. Because they are difficult or impossible to confidently distinguish without the use of microscopic traits, most of the occurrences of these taxa are recorded by academics, and then fairly infrequently. Luckily, community-based labs are popping up all over the country to fill the demand for small, shared, community lab space. Where I live in Eugene, Oregon, there is a community lab with amazing resources run by a local non-profit called the Thinkubator. It costs $10 per day for drop-ins, or you can get monthly subscriptions which give you dedicated space in the lab. Many mycology clubs are beginning to have microscopes and culture labs as well. I was at the Oregon Mycological Society meeting in April and saw a small laminar flow hood set up with the specimens in the back, and an enthusiastic young man using careful sterile technique, taking tissue from oyster mushrooms that another club member had collected and starting cultures on agar petri dishes.

Even if there is no community laboratory near you, nor any clubs or groups with lab equipment, Xylaria are absurdly easy to preserve for later examination. Place your collection in a paper bag (I know mycologists that save all the envelopes from their junk mail for this purpose) and leave it to air-dry indoors for several days to a week. You may see a spore print form on the paper, with spores shot through the opening of each perithecium, leaving little black dots under the fruiting bodies. Once your Xylaria is dry, wrap it in paper and you’re done! You may want to place it in the freezer for a few days to kill off any beetle larvae or mites, which will degrade you collection over time, but otherwise, air-drying preserves Xylaria very well; because they are so carbonaceous, a dehydrator isn’t necessary to save these sturdy fungi. Once they’re preserved, you can save them to examine when you have access to a microscope, or mail them to someone willing to look at the spores for you. Remember though, to identify Xylaria fully, you must have mature ascospores. If you cut it in half, the perithecia should appear black and full of a viscous goop when fresh (that’s the spores in their asci). If the perithecia are white, it means the specimen is not mature, and, sadly, will not be able to be identified. Use your hand lens because the perithecia can be quite small, usually about a millimeter across.

But why bother? What’s the point of saving, identifying, and recording these strange little fungi? The state of knowledge for fungi like this is so incomplete in part because few people look for these fungi. There are great discoveries to be made even in our own backyards, to say nothing of the undiscovered diversity waiting patiently in tropical rain forests. Just last spring, I joined the Pacific Northwest Key Council for their annual spring foray at Mount Hood here in Oregon. It might have been the first time in more than a century that someone with a particular interest in flask fungi had collected on that slope. We collected Xylaria hypoxylon, but also another species of Xylaria—growing from tuberous sclerotia buried in a much-decayed Hemlock log—which seems to be new to science. It wasn’t difficult to find; all it took was looking. We also found a small, closely related fungus called Nemania kellermanii. Up until last spring, this little fungus was known only from a single collection, from Ohio, from more than one hundred years ago. I believe this beautiful but tiny relative of Xylaria has only been collected twice in the world, most of a continent and more than a century apart, not because it is particularly rare, but because no one is looking. What new treasures might we discover if we only paid attention?

Xylaria schweinitzii, illustration by the author. To the left, a mature fruiting body and three immature fruiting bodies. Mature Xylaria schweinitzii may be quite large, more than 12 cm tall in many cases. In the center, a detail of the surface of a mature fruiting body, with a cut-away showing the round perithecia completely embedded. To the right, spores in asci, and a close up of the spores and ascus tip, showing the characteristic diagonal, short germ slit in the spores, and the inverted-hat shaped apical plug in the ascus.

Xylaria schweinitzii, illustration by the author. To the left, a mature fruiting body and three immature fruiting bodies. Mature Xylaria schweinitzii may be quite large, more than 12 cm tall in many cases. In the center, a detail of the surface of a mature fruiting body, with a cut-away showing the round perithecia completely embedded. To the right, spores in asci, and a close up of the spores and ascus tip, showing the characteristic diagonal, short germ slit in the spores, and the inverted-hat shaped apical plug in the ascus.

What next: crowdfunding and taxonomy

Unfortunately, simply paying attention is not quite enough. Without skilled taxonomists to write guides and keys (like those in the Further Reading section), even the most skilled observer may not be able to confidently identify a specimen, to determine if it is a new record, or even a new species. The number of taxonomists—not just fungal taxonomists, but all taxonomists—is shrinking right now. Federal support of research in the US is in the longest decline ever recorded, and as the budgets shrink, the first things that get cut are basic, less “sexy” branches of science, such as taxonomy and natural history. But, without funding for such basic science, the existing taxonomists are nearing retirement, and training no replacements. Soon no one will be able to classify new species in relation to the existing body of knowledge. No one will be able to write identification keys or species descriptions.

I believe that we, as advocates for science and lovers of the beauty of nature, can help to solve this problem. Federal funding for taxonomic projects may be in decline, but there are many people who recognize the value of this work and are interested in seeing its products take shape: books and papers allowing for the identification of a group of organisms. Crowdfunding provides a new option for funding taxonomic research by letting the people interested in supporting the work do so directly. Crowdfunding science has had pretty mixed success—generally, crowdfunding efforts are most successful when there is some tangible reward, and much of science does not allow for this. The reward of science is generally societal, not individual: it lifts us all up equally. This is why science, like other public services, is traditionally funded through taxes. Taxonomy, however, typically has a much more tangible product than other sciences, and one that has the potential to be much more accessible: a work describing, classifying, and illustrating a group of organisms. If done well, taxonomic works can be functional, allowing people to confidently identify organisms they are interested in, as well as beautiful, full of lovely photographs or stunning illustrations. In this way, taxonomic projects become graphics projects as well. People who may not be interested in science for the sake of science may be interested in the beauty of technical botanical illustrations, or photography of creatures they have never seen. This graphic element allows for the creation of meaningful rewards beyond a paper or a book detailing the taxonomic study at hand, allowing the project to reach, and be funded by, a much larger audience.

I intend to test this theory using my knowledge of Xylaria by launching a Kickstarter campaign to convert my hard-fought taxonomic understanding of this group into a thorough, careful taxonomic treatment for the Ecuadorian cloud forests. This work will be both functional, and beautiful: it will include nearly 50 species, drawing from the extensive collections of Ecuadorian cloud forest Xylaria that my lab and I made in conjunction with my dissertation research, as well as the hundreds of cloud forest Xylaria collections from the Ecuadorian National Herbarium in Quito and other herbaria around the world. I am working with other experts in the Xylariaceae to ensure the best taxonomy possible, and I am creating nearly 100 high quality drawings to illustrate each and every species (for example, Fig. 4). There will be a color photo supplement including as many taxa as possible, photographed in Ecuador by Mr. Danny Newman (Figs. 2 & 3). No other work on Xylaria this century will be as well illustrated. Many ancillary rewards will use these drawings and Mr. Newman’s photography for everything from stickers to a Xylaria-themed paisley handkerchief, increasing the campaign’s appeal beyond just those interested in identifying perithecial Ascomycetes.  

You can follow the progress of this work here at Xylaria.net, where I’ll be documenting new species and posting about the art and the science of taxonomy, among other things. If you would like to help with this proof-of-concept for mycological taxonomic crowdfunding, you can join the mailing list from the website to get notifications, including when the campaign starts. I’ll be posting periodic updates as we lead into the crowdfunding effort, covering the progress of the project: the creation of the Xylaria illustrations, keys, and other taxonomic work.

I think it’s important to remember that projects like this one don’t just breathe a little life into the study of a particular group of organisms, like the Xylaria, they send a strong message about the importance of basic scientific research, and the need for taxonomy and natural history. We have the power to support the science we want to see in the world.


Further Reading:

Dennis, R. W. G. (1956). Some Xylarias of Tropical America. Kew Bulletin, 11(3), 401–444.

Hladki, A. I., & Romero, A. I. (2010). A preliminary account of Xylaria in the Tucuman Province, Argentina, with a key to the known species from the Northern Provinces. Fungal Diversity42(1), 79-96.

Rogers, J. D. (1979). Xylaria magnoliae sp. nov. and comments on several other fruit-inhabiting species. Canadian Journal of Botany57(8), 941–945.

Rogers, J. D. (1983). Xylaria bulbosa, Xylaria curta, and Xylaria longipes in Continental United States. Mycologia 75, 457–467.

Rogers, J. D. (1984). Xylaria acuta, Xylaria cornu-damae, and Xylaria mali in Continental United States. Mycologia 76, 23–33.

Rogers, J. D. (1984). Xylaria cubensis and its anamorph Xylocoremium flabelliforme, Xylaria allantoidea and Xylaria poitei in Continental United States. Mycologia 76, 912–923.

Rogers, J. D. (1986). Provisional keys to Xylaria species in continental United States. Mycotaxon26, 85–97.

Rogers, J. D., & Callan, B. E. (1986). Xylaria polymorpha and its allies in continental United States. Mycologia, 391–400.

Rogers, J. D., Miller, A. N., & Vasilyeva, L. N. (2008). Pyrenomycetes of the Great Smoky Mountains National Park. VI. Kretzschmaria, Nemania, Rosellinia and Xylaria (Xylariaceae). Fungal Diversity, 29, 107–116.

San Martín González, F., & Rogers, J. D. (1989). A preliminary account of Xylaria of Mexico. Mycotaxon, 34(2) 283–373.

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