The majority of species featured in these weekly editions of Fungi Friday either break down dead plant matter, parasitize plants or animals, or form crazy intricate mutualisms with other organisms. An exceedingly wide diversity of fungi carry out the different aforementioned ecological roles, so it's always exciting to come across a fungus new to me, that has evolved a different strategy. Everybody, I’d like you to meet Onygena equina, a species commonly known as the horn stalkball. It’s a keratin specialist that breaks down the horns and hoofs of sheep, horses, and cattle.

The closely related Onygena corvina too utilizes keratin, but only from feathers, owl pellets and hair. Onygena equina has a taste for the harder keratinized tissue. O. equina is also quite rare, which may help explain why very little information is published regarding this species. The most informative paper I found about this horn stalkball was published in 1899 by British botanist Harry Marshall Ward! He was actually the first individual to successfully cultivate the fungus, which led to the adequate description of its life cycle. But since then, there has been next to nothing published on this peculiar little fungus. 

Ward’s comprehensive research carried out 120 years ago has given us invaluable insight about the ecology of this unique saprotroph. While he was coming up with growth media to successfully germinate Onygena spores, he figured out that treating the spores with gastric juices from bovine herbivores greatly enhanced spore gemination. Additionally, Ward figured out that products found within bovine feces too promoted spore germination. Along with these two realized nutritional requirements, the ecological strategy of this fungus was also comprehended. 

The spores of this fungus come from small fruiting bodies, reaching the maximum height of 8 millimeters. Most spores released land on grassy plant tissue. Cattle, horses and sheep eat these grasses with the spores on them, and thereby pass them through their gut. Animals that excrete near horns and hoofs of dead bovine and equine herbivores inoculate the keratin rich substrate with viable spores of this voracious specialist fungus. 

It seems like many things have to go right for the fruiting of this fungus. This most likely contributes to its rarity. Because humans manage pastures so heavily, it is rare for a dead body of a sheep, horse, or cow to be left alone on a grassland where other animals are still grazing. In fear of the spread of different diseases, these dead animals, when found are removed from the grasslands. Additionally, another filter working against this species of fungus is that on human managed pastures, these herbivores almost never die of natural causes in the fields they graze on. These animals instead soon meet their final fate; to be killed and processed for human and human pet consumption. The unique habitat of unadulterated grasslands with large feeding herbivores is as rare as the fungus itself. 

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