Caloplaca stellata Wetmore & Karnefelt
A Species of Firedot Lichen
Basis for Listing
Caloplaca stellata (a species of firedot lichen) was first recognized as a species in 1998 by Clifford Wetmore and Einar Kärnefelt, who officially described it based on a specimen collected by Bruce Fink in 1897 from Grand Portage, Minnesota (Wetmore and Kärnefelt 1998). Despite the fact that the type locality of C. stellata is in Minnesota, the species is more typical of western North America, particularly California and the desert southwest, where it appears to be fairly common (CNALH 2016). Outside of California and the Sonoran Desert region, C. stellata is also known from scattered sites in British Columbia, Oregon, Idaho, Montana, and the Black Hills of South Dakota. In the Great Lakes region, C. stellata is known from a few scattered sites in Minnesota and a lone collection from Isle Royale National Park in Michigan. Due to the apparent rarity and disjunct distribution of this species in Minnesota, C. stellata was listed as a special concern species in 2013.
Caloplaca stellata is a bright orange crustose (crust-like) species that gets its specific epithet from the star-like appearance of typically formed thalli. The species appears to be unique in the genus, with no close relatives (Wetmore and Kärnefelt 1998). In Minnesota, C. stellata can be differentiated from other orange crustose lichens by its small star-shaped thallus and the presence of soredia at the tips of the lobes (Wetmore and Kärnefelt 1998).
In Minnesota, C. stellata has only been collected a handful of times, making it difficult to draw conclusions on habitat preference. Although C. stellata has been collected from two distinct community types, the majority of collections are from northern Minnesota (Border Lakes Subsection), where the species apparently grows on sheltered portions of diabase in cliff and talus communities. The lone collection of this species from the southeastern portion of the state (The Blufflands) is from a bluff overlooking the Zumbro River. Although the specific type of rock on which C. stellata was found in Wabasha County is unknown, sandstone is the most likely candidate since the species appears to favor non-calcareous rocks (Nash et al. 2001). Although this species has not been recorded from rock outcrops in the state, it seems likely that it could be found in these systems.
Biology / Life History
According to Wetmore and Kärnefelt (1998), C. stellata rarely produces apothecia, so the species likely reproduces asexually through the dispersal of soredia. Soredia are reproductive structures that contain both fungal and algal partners and can be dispersed over short distances. This species may also reproduce sexually through the distribution of spores; however, this appears to be extremely rare.
Conservation / Management
Although all the known populations of C. stellata in northern Minnesota are located in protected areas, the cliff/talus communities on which C. stellata occurs are dynamic but fragile systems. Shifting rocks or rock slides could bury entire populations of this species. Anthropogenic disturbance to this and other talus slopes is likely the main threat to the perpetuation of this species in the state. Hikers and sightseers would likely be the primary causes of decline for this species in northern Minnesota. Efforts should be made to minimize impacts to the talus slopes on which C. stellata occurs. The southern Minnesota population of C. stellata likely occurs on sandstone, which has experienced heavy pressures from the silica sand industry due to its use in hydraulic fracturing. Efforts should be made to protect sandstone outcrops where C. stellata occurs.
Best Time to Search
Caloplaca stellata can be observed year-round, whenever lichens are not covered by snow or ice.