genus Exobasidium

Member of family Exobasidiaceae
basidiomycete fungi (phylum Basidiomycota)
gall fungi
fungi including lichens (kingdom Fungi)

Caution: There may be other wild species of this genus not yet included in this guide.

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This genus parasitizes bearberries and manzanitas (genus Arctostaphylos) and others in the heath family (family Ericaceae).

Ron Russo’s popular reference for California galls lists lingonberry gall (Exobasidium vaccinii) as forming galls on numerous plant hosts. However, discussions on iNaturalist have cast doubt on this interpretation. A timeline:

• 1885 Casey (free) briefly describes Exobasidium arctostaphyli on bearberries and manzanitas (genus Arctostaphylos).
• 1915 Burt (free) lumps galls on many hosts into lingonberry gall (Exobasidium vaccinii).
• 1959 Savile (req. subscription) mostly agrees with Burt, but retains Exobasidium arctostaphyli as a distinct entity.
• 1981 Nannfeldt (citation only) proposes that lingonberry gall (Exobasidium vaccinii) is found only on lingonberry (Vaccinium vitis-idaea).
• More recent studies tend to agree, e.g. as described in the introduction to 2012 Kennedy (free).
• 2022 Schwab adds Exobasidium arctostaphyli to iNaturalist, and Asquith in particular starts adding this ID to many observations.
• Schwab believes that although the original 1885 description includes infections of both leaves and young shoots, only leaf infections should be included in Exobasidium arctostaphyli.
• 2022 gallformers.org adds Exobasidium a-spp-whole-shoot-discoloration as a placeholder name for infections of whole shoots.
• Until these are properly researched, these should be identified in iNaturalist only as genus Exobasidium with the observation field “Gallformers Code: a-spp-whole-shoot-discoloration.”

Relevent iNaturalist comments in chronological order: 1, 2, 3, 4, 5, 6.

lingonberry gall
Exobasidium vaccinii

• parasitizes only lingonbery (Vaccinium vitis-idaea)
• see genus Exobasidium for discussion

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2 observed taxons / 1 unobserved taxon / 1 key

Chris’s observations: 6 (all are research grade)

Locations:

• Castle Rock SP: 2
• Mt. Madonna SP: 2
• Purisima Creek Redwoods OSP
• Skyline Ridge OSP

Months:

• Jun.: 4
• Jul.: 2

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Taxon info: iNaturalist

Bay Area species: iNaturalist