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Chaga; The Elusive Fruiting Body of Inonotus obliquus (Chaga)
Found on MMA Foray

Greg Marley, Mushrooms for Health

Chaga Sclerotium
Sclerotium with tube layer exposed
after bark is removed
Chaga Ridges
Ridge of thick tubes serve to force
the bark layer apart
Chaga Silvery Tubes
Close-up of silvery gray tube layer
Chaga Tube Thicker
Area where the tube layer thickens
Chaga Tubes Close
Close-up pf pore openings and tubes

Chaga is an easily recognized black and charred-appearing fungal mass found primarily on the trunks of mature birch. The irregular black growth of Chaga is the most visible sign of Inonotus obliquus, also called the Birch Clinker. I. obliquus attacks live birch through wounds or broken branches. The spores germinate, allowing the mycelium to establish itself, growing through the sapwood and into the heartwood. The black mass is composed of the fungal hyphal tissue and grows during the warmer months through a poorly understood interaction between the fungus and the tree’s protective efforts. The fungus is most often described as a parasite, with the growth derived from the mycelium feeding on the sap of the tree as well as the heartwood. It is variously called a sterile conk or a sclerotium. I struggle with the label sterile conk as I would expect it to have all the features of a fruiting body, lacking only spore production. In this case, the mass of hyphae has no level of organization of tissues that characterize most sporocarps. I can find no other use of the term sterile conk with other fungi. Some experts have argued that it is not a sclerotium either; claiming that while it is a mass of hyphal tissue, there is little evidence that it fuels the later development of a fruiting body, the classic purpose of a sclerotial body. I question this conclusion; I. obliquus reportedly fruits only after a tree dies and after tree death the Chaga mass also dies back. Could the hyphal energy packed into the sclerotial mass help fuel the growth of the fruiting body? The timing alone suggests this is probable.

By most reports, the actual spore-producing body of I. obliquusis very rarely seen. Not only foragers and amateur mycologists, but mycologists who have studied the species report that the fungus fruits only once in its life cycle, generally 2-4 years after the tree dies, weakened by the parasite, from cutting or other damage. Fruiting has also been observed when a portion of a birch infected with the fungus dies, leaving the rest of the tree alive. I have been actively observing, collecting and using Chaga for more than a decade and have seen evidence of its fruiting body only once before this past month. The first time was when I came upon an old desiccated layer of tubes surrounding a Chaga wound on a dead paper birch. Never having seen even a
good photo, I was unsure that my find really was the fruiting body of Chaga.

During the final foray of the 2014 season, held at the Viles Arboretum in Augusta on November 1, I was fortunate enough to investigate a dead birch that didn’t look quite normal, and discovered a massive fruiting of I. obliquus. What caught my eye was the fracturing of the bark on this 10 inch diameter trunk of a tree that appeared to have been dead for 2-3 years. In three places along the trunk, I could see the classic Chaga sclerotium growth, clearly dead and crumbling. The bark had split and broken away from the sapwood in very irregular splits and chunks. This was entirely different from what we usually see Commonly, as the outer, impervious layer of birch bark comes off a dead tree, it peels around the trunk, along lines of tear that are perpendicular to the line of the trunk. When I looked more closely I saw a layer of polypore tissue attached to the sapwood, and resupinate between the sapwood and bark cambium. In certain areas the fruiting body tissue was quite thick, over an inch in depth and, clearly, it was the pressure of this expanding tissue that forced the bark to fracture with almost explosive force. As the bark loosened, it exposed the pore openings of the hymenial tubes to the air, thereby allowing air currents to disperse the spores. Unlike my first find of Chaga fruiting, which was limited to the opening of a wound on the trunk of a dead birch, this sporocarp was expansive, growing around the circumference of the trunk and stretching from almost ground level to at least 8-10 feet above the ground. From the photos you can see that it looks like an undulating surface of grayish tube openings. The fruiting body ranges from just a few millimeters, to ridges over 3 cm thick. Think of these thick ridges and “pillars” as buttresses growing outward, pushing against the inner surface of the cambium or bark, creating space for additional spore-bearing tissue to form. When, as with this tree, the bark fractures and loosens, it allows air currents to reach the pore openings and allow for better spore dispersal.


Mycologists and ecologists studying I. obliquus in Europe complain of the difficulty in studying the fruiting body because they report that it is very quickly attacked and consumed by several species of beetles that gorge on the fresh tissue for the quality of food it represents. They hypothesize that the beetles may play a role in spreading the spores out into the world, aiding the wind dispersal. They also report that fruiting bodies are generally greatly degraded within a couple of days. The tree at Viles showed no signs of predation and when I returned for another look 2 weeks and 4 weeks later, the tissue showed no signs of damage or of decay. There was no indication that this would be a quickly degraded growth as reported in the literature. Could this be due to the cold weather this late in the season causing die-off of insect predators, or does this region of North America lack the beetles that devour it in Scandinavia? Another alternative explanation is that this rarely found sexual growth is not well understood and may be more persistent than that seen in Europe.

Having found one example of fresh fruiting of this shy sporocarp, I have great hope that I can use the experience to locate other examples in the state over the coming years.

From a place of relative obscurity up to the past decade, Chaga has become among the most talked about of the medicinal mushrooms. It has become popular as a tea and makes the base of a good chai. When I first began offering medicinal mushroom talks and workshops more than a decade ago, Chaga was almost unknown, relegated to a few people well-versed in herbal medicine. Widely used as a staple in traditional medicine in Siberia and Russia for the past 3-4 centuries, its virtues were unknown in the US. Chaga is now in demand as a dietary supplement and alternative medicine across much of Asia, Europe and now, North America. In Maine Chaga is sought out by many people and its popularity has led to concern over the sustainability of the supply. A Chaga sclerotium grows slowly, taking at least 4-6 years to attain harvestable size. I urge people to harvest carefully and to take only what they know they can use.