In October 2017, I visited Palomar Mountain State Park, San Diego County, California to collect acorns of the interior live oak, Quercus wislizeni (Section Lobatae), for an investigation of oak hybridization at that location. Following the first day on site, while reviewing the day’s leaf samples, acorns, and photographs, a chance photo with an oblique view suggested that one individual Q. wislizeni bore yellow or golden hairs on the abaxial leaf surface.

North America is home to 91 species of oak trees. Astoundingly, the various species rarely, if ever, occur alone. Where one kind of oak is found, invariably at least one more will be found. How can nature support a setup like that when it operates on the principle that only the fittest survive in any one setting?

Plant pathologists from the California Department of Agriculture (CDFA) recently identified a new species of fungal pathogen that infects oak, chinkapins, and tanoaks. Until recently, North American diagnosticians called all species of the genus Tubakia that infects oaks in North America, Tubakia dryina, because they all have very similar morphological features to this European fungus. However, a new study shows that the North American species vary genetically from Tubakia dryina. Among these is the newly recognized California species.