When shopping for aquarium decorations at the pet store, one isn’t usually thinking about invasive tree pathogens. Based on new evidence, though, maybe we should—mysterious black growths on submerged decorative wood from freshwater aquariums in the states of Minnesota and Colorado were revealed to be Xylaria apoda, a fungus not previously reported in the United States. In research funded in part by the Minnesota Invasive Terrestrial Plants and Pests Center, Bob Blanchette, Nick Rajtar, and Ben Held made this identification.
The wood available at American retail stores for aquariums is typically imported from tropical forests of Asian countries. Chosen for distinctive curly or gnarly branches, this “spiderwood” comes from perennial woody plants like Rhododendron. Driftwood from forest floors is also used. Studies in Amazonian and Asian rainforests show diverse Xylaria fungal species, though these are typically not found on submerged wood, though some studies indicate exceptions.
When an aquarium enthusiast found odd black growths coming off their aquarium wood, he contacted Blanchette to figure out what this was. Some of the wood and suspected fungal growth were obtained, which they then isolated, cultured, incubated, and tested whether underwater fungal fruiting could be duplicated using the cultured fungus and sanitized spiderwood from an aquarium store. The lab also identified the fungal culture by using pure cultures to extract and sequence the DNA, revealing it to be Xylaria apoda. After identifying it, another suspected Xylaria was seen and reported on social media. This one from Colorado which turned out to be the same fungus.
These results have opened opportunities to further study Xylaria aplodia, both in its native Asian countries and in the United States where it has demonstrated versatility, including living for two years fully underwater in an indoor aquarium. Additionally, this study carries an important reminder that shipments of tropical wood can carry foreign fungi (Xylaria and others) as well as potential plant pathogens. If wood is not properly sanitized before export (as we see with the Asian aquarium woods) there is a serious danger of introducing exotic species that may be detrimental to our urban and forest landscapes. This study has revealed a previously unknown avenue for foreign fungi to enter the United States and it sounds an alert to make sure this wood is treated properly to exclude microbes before export.
Read the whole paper:
Blanchette, R. A., Rajtar, N. N., Yandrasits, H., Stephens, K. C., & Held, B. W. (2025). Aquatic Xylaria: an exotic fungus introduced into the United States on aquarium decorative wood. Mycologia 117. https://doi.org/10.1080/00275514.2025.2451522