In Europe, there are two, possibly conspecific, species of Synchytrium that use Plantago as host: S. aureum, with golden yellow pustules, and S. plantagineum, with golden-red pustules that turn black.
This has red pustules and grows on Plantago erecta, a plant native to Oregon, California, and Baja California.
”- Gallformers Contributors: (2024) Gallformers ID Notes©