The Fungi that make Alder Tongue Galls
Although I have probably walked past them dozens of times, I first noticed alder tongue gall a few months ago when I noticed what appeared to be bright red flowers on an alder shrub. I took a few photos and added the observation to iNat, and the artificial intelligence suggested an identification of Taphrina alni.
I was intrigued, and tried to find out more about these strange-looking growths, but information on the web was pretty scanty. The only references I was able to locate indicated that T. alni occurred in Europe, and had recently been found in Great Britain. There was no indication that it was a new world species.
With the obligatory disclaimer that I am not a mycologist (nor do I play one on TV) my research so far indicates that there are three species of Taphrina that cause alder tongue gall, which can be distinguished by microscopic or molecular analysis, but are generally differentiated by geographic distribution. These species are:
Taphrina alni, which occurs in Europe. The studies cited below indicate that T. alni has not been found in North America with the exception of some specimens collected in Alaska under the synonym Taphrina amentorum.
Taphrina robinsoniana occurs in eastern North America.
Taphrina occidentalis occurs in western North America.
Ray (1939) is the primary reference; he found that alder tongue gall in North America is not caused by T. alni but rather by T. robinsoniana and by a previously undescribed fungus which he named T. occidentalis (https://www.jstor.org/stable/3754433).
Mix (1949) in his "Monograph of the Genus Taphrina" accepted Ray's findings with regard to the alder tongue gall forming species, with the exception that Ray had described another species T. rugosa which was determined to be a juvenile form of T. robinsoniana (https://www.biodiversitylibrary.org/part/16125#/summary).
Dugan & Newcombe (2007) summarized the state of knowledge with regards to alder tongue gall fungi and noted the discovery of specimens in Idaho consistent with Ray's description of T. occidentalis. They note that additional specimens of T. amentorum have been found in Alaska but not elsewhere. They also note that the "relation between T. amentorum and T. occidentalis appears not substantially investigated since the publications of Mix (1940) and Ray (1939)." (https://www.researchgate.net/publication/43270414_New_records_for_powdery_mildews_and_Taphrina_species_in_Idaho_and_Washington).
Rodrigues & Fonseca (2003) found that T. alni and T. robinsoniana can be differentiated using DNA analysis. T. robinsoniana may in fact encompass more than one cryptic species. T. occidentalis was not included in their study (http://ijs.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.02437-0?crawler=true&mimetype=application/pdf).
