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A common sight across north central Texas and the Edwards's plateau is a white or light gray fungus that appears as a whitening pattern on the branches of young Juniperus Ashei trees. Most folks that venture out into wooded areas where J. Ashei occurs will notice the distinctive pattern formed by this fungus. But very few know exactly what it is. With this journal post, I hope to help fill that gap by providing a useful summary of this common fungus along with a list of references for further study. I also want to acknowledge Mark Gustafson who described this fungus in an entry in his recent book, A Naturalist's Guide to the Texas Hill Country.

In 1910, Heald and Wolf described this fungus species and assigned it the name Cyanospora albicedrae. The generic name Cyanospora was based on the (apparently incorrect) observation that the spores were green. The following year Saccardo and Traverso corrected this and assigned the species to the genus Robergea.

When you see this fungus in the field, look for small gray nodules on the whitened patches. These contain the fruiting bodies from which the filamentous spores are expelled. The close-up photo below shows an example of these gray nodules.

This fungus occurs only on J. Ashei. It is quite common on the branches of young trees, especially in shaded conditions such as dense brakes. In fact, it is so common that it can be used as a characteristic feature in the identification of J. Ashei. Since it only occurs on this one species of tree, the range of R. albicedrae can be expected to be within the range of J. Ashei. The map below shows the natural range of J. Ashei.

According to the 1910 paper by Heald and Wolf, the fungus is probably parasitic on the host tree. They also indicated that branches of the tree or even the entire tree could be killed by the effects of the fungus corroding the bark and destroying the cambium layer. A 2008 paper by Miller and Lemke supported the possibility that the fungus is parasitic on J. Ashei. They found that tree size (height and basal trunk diameter) decreased corresponding to increased fungal load.

References

Heald, F. D., and F. A. Wolf. “The Whitening of the Mountain Cedar, Sabina Sabinoides (H.B.K.) Small.” Mycologia, vol. 2, no. 5, 1910, pp. 205–212. www.jstor.org/stable/3753277.

Sherwood, M. A. "The Ostropalean Fungi. I." Mycotaxon (1977).

Miller, S. A. and D. E. Lemke. 2008. Determining the relationship between Cyanospora albicedrae (Ascomycota: Stictidaceae) and Juniperus Ashei (Magnoliophyta: Cupressaceae). Annual meeting of the Texas Academy of Science, Texas A&M University, Corpus Christi.

Gustafson, Mark. A Naturalist's Guide to the Texas Hill Country. Vol. 50. Texas A&M University Press, 2015.

Juniperus Ashei range map by Elbert L. Little, Jr., of the U.S. Department of Agriculture, Forest Service [Public domain], via Wikimedia Commons