Thelomma ocellatum

Thelomma ocellatum is a crustose lichen inactive species that belonged to the family Caliciaceae. It was first described by Körber and later reassigned by Tibell in 1976. Since 2020, the species has been declared inactive and was swapped with Pseudothelomma ocellatum.

Although frequently sterile, the species can sometimes be found with apothecia that are reminiscent of the related lichen Cyphelium inquinans. Thelomma ocellatum is always sorediate-isidiate.

Description
Thelomma ocellatum (Körb.) Tibell is a dense gray crust covered in raised warts, featuring dark grain-like structures called soredioid isidia. Though often lacking reproductive structures, it occasionally bears apothecia, resembling those of Cyphelium inquinans (Sm.) Trev., albeit consistently embedded within a rim of thallus. Certain robust specimens of Cyphelium, with apothecia either sessile or partially immersed, closely resemble Thelomma (like T. ocellatum and T. occidentale (Herre) Tibell). However, a reliable distinction lies in Thelomma 's pale exciple sides, contrasting with the dark exciple of Cyphelium.

Distribution
Thelomma ocellatum was initially documented in North America by Weber in 1967, but the specimen was later reclassified as Thelomma occidentale. The first officially recognized occurrence of T. ocellatum in North America was reported by Tibell in 1978, originating from Riverside County, California. Following its initial documentation, the range of Thelomma ocellatum was observed to extend from central British Columbia to southern California and inland to central Montana. Nevertheless, occurrences west of the Cascade crest in Oregon and Washington are sparse, and the species is notably absent from extremely coastal areas.

Further investigations revealed its prevalence between the Cascade crest and the Continental Divide, with sporadic occurrences to the west of the Cascade and Sierra crests. Researchers extensively explored regional and national herbaria, uncovering new locations in the Pacific Northwest and Rocky Mountains. While the species was largely absent from most herbaria, a few specimens were identified under the name Cyphelium inquinans.

A significant range extension was reported in 2011 from the Yukon Territory in northern Canada.

Ecology
Thelomma ocellatum exhibits a high specificity in its habitat requirements, typically colonizing bare wood surfaces. It thrives in nitrophilic environments and is predominantly found on bird perches, with fenceposts being a common substrate. Additionally, it can be spotted on aged stumps, dead branch stubs, and elevated tree roots exposed by tip-ups. The distribution pattern of T. ocellatum on the fan-like array of tree roots on tip-ups highlights its nitrophilic nature, as it specifically inhabits roots frequently utilized as bird perches.

Dispersal of Thelomma ocellatum primarily occurs through vegetative means, with both spores and diaspores likely disseminated by birds frequenting the substrates it inhabits. Unlike many ascomycetes, Thelomma and other mazaedium-producing species accumulate spores that are dispersed by external agents rather than being forcefully ejected. The likelihood of encountering T. ocellatum increases with the age of the wooden substrate, possibly due to extended opportunities for propagules to colonize or an enhancement in substrate quality over time.

While the geographic separation of the Yukon populations from the previously known range made identification tentative, molecular data confirmed the placement of the Yukon material within T. ocellatum.

Taxonomy swap
A taxonomic swap was committed on February 20, 2020, to replace Thelomma ocellatum with the new name Pseudothelomma ocellatum.