The species was originally described as Caeoma torreyae before being combined in the new genus Rogerpetersonia. There are no other synonyms.

Rogerpetersonia torreyae is a rust known only from Torreya californica, which is itself a species assessed as VU and confined to a few relictual populations in California, some of which are susceptible to fire. Additionally, R. torreyae is monotypic, so it may be an EDGE species, and is one of the earliest diverging rust fungi.

The species is endemic to California, USA. It is an obligate pathogen of Torreya californica, which itself occurs in ~25 relictual populations from southwest Trinity County south to Monterey County in the coastal range, and from Shasta County south to Tulare County in the Cascade-Sierra Nevada foothills (Griffin & Critchfield 1972; Thompson et al. 1999).

R. torreyae is an obligate pathogen of Torreya californica; therefore, its population and trends are tied to its host. Torreya california was assessed as vulnerable in 2011 because “past logging has virtually eliminated Torreya californica from parts of its historic range and also removed most of the large trees across almost all of its range. Regrowth is reported to be very slow. On this basis a past decline of more than 50% of mature trees in the population has been inferred over the past 150 years (three generations), leading to an assessment of Vulnerable under the A1 criterion” (Farjon 2013).

In the 2011 assessment, it noted that the decline of T. californica had ceased or virtually ceased, but no mention was made of wildfires. Torreya california is generally top-killed by fire, later resprouting from the roots, root crown, and bole (Howard 1992). It is unclear how increased fire frequency and severity will impact this species, but it is slow-growing, slow to mature, dioecious, and in fragmented populations, several of which are threatened by fires.

Rogerpetersonia torreyae is an obligate pathogen of Torreya californica. Torreya californica is confined to ~25 disjunct, relictual populations in the coastal range and Sierra Nevada foothills. It is a slow-growing, shade-tolerant tree. Rogerpetersonia develops on newer leaves (from the current year’s growth of this evergreen tree) from September to November, and is more abundant on young plants (Bonar 1951). The alternative host is unknown.

The main threats to R. torreyae are those to its host, T. californica, which primarily are the increase in the frequency and intensity of fires.

Populations of the host, T. californica, can be protected, and natural populations can be augmented by seed collection, propagation, and planting.

Estimating the percentage of T. californica trees hosting R. torreyae, the percentage of leaves on a host tree effected, when present, and the number aecia on effected leaves may help estimate populations of R. torreyae. Additionally, updated distribution maps and population estimates of T. californica could also help estimate populations of R. torreyae.

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