Platismatia glauca (L.) Culb. & C. Culb.
Basis for Listing
Platismatia glauca (ragbag lichen) is a widespread species in North America (Brodo et al. 2001), where it appears to be fairly common along the Pacific and Atlantic coasts, particularly in the northern portions of each. In the Great Lakes region, P. glauca has been recorded from Ontario, Michigan, Wisconsin, and Minnesota, where it appears to be much less common. This species reaches the western extent of its mid-continental range in Minnesota, where it has only been recorded a handful of times from sites within close proximity to Lake Superior (North Shore Highlands).
Platismatia glauca was first collected in Minnesota in 1951 from an island in extreme northeastern Cook County. Two additional populations were located in this same area in 1980. More recent surveys in Lake and Cook counties have located only one additional population of P. glauca. Because of the apparent rarity of this distinctive species in Minnesota, P. glauca was listed as a special concern species in 2013.
Platismatia glauca is a foliose (leaf-like) lichen, with a whitish-grey thallus that becomes greenish when wet. The underside is typically shiny black, with a brown margin that may have patches of white. Rhizines are simple or branched and are typically sparse; and the lobes are ascending from the substrate. The thallus is sorediate, with white soredia forming “…in laminal, rounded to irregular soralia or marginal, crescent-shaped soralia” (Nash et al., 2001).
In Minnesota, P. glauca is unique in having the above aforementioned combination of characteristics. The closely related P. tuckermanii (Tuckerman’s ragged lichen) is the only species likely to be confused with P. glauca. The most important characteristic for separating the two species is the presence of soredia along the lobe margins in P. glauca. In addition, P. glauca is typically sterile, only producing apothecia in extremely rare situations, while P. tuckermanii regularly produces reddish-brown apothecia.
In Minnesota, P. glauca has been collected too few times to draw firm conclusions on substrate preference. Most of the known populations were observed growing on small cliffs or rock outcrops, while one was found on the trunk of a Picea mariana (black spruce). It is likely that this species simply requires a stable substrate, such as rock or long-lived trees. Perhaps the most noteworthy habitat feature of each of the known populations of P. glauca in Minnesota is the fact that they are all restricted to small islands in Lake Superior. The Cook County populations are all from islands characterized by old-growth fir forests, with abundant lichen and bryophyte cover. The Lake County site was found growing on talus associated with a cliff on a small unnamed island. This habitat preference is likely due to the climate modifying effect of Lake Superior. Platismatia glauca has not been found along the mainland in the same area as the islands despite the fact that similar habitat exists there.
Biology / Life History
Platismatia glauca likely reproduces asexually by fragmenting and through the dispersal of soredia, both of which can be disseminated by wind, animal, water, etc. It is also possible that this species reproduces by spores, though fertile specimens are apparently extremely rare.
Conservation / Management
All the known sites for P. glauca in Minnesota are on small islands in Lake Superior that are owned and protected by the Grand Portage Indian Reservation. If P. glauca still persists at the known locations, they are likely protected from most anthropogenic disturbances. Throughout much of its range, loss of habitat is the primary threat to this species' survival. All types of intense developments or heavy recreational activity can negatively alter the habitats where this and other rare lichens occur. Efforts should be made to minimize damage to old-growth forests to protect this and other rare lichen species.
Best Time to Search
Searches for P. glauca can be conducted year-round, whenever they are not covered by snow or ice.