Rare Species Guide

  Synonyms

Physcia obscurata, Anaptychia sorediifera, Peltula obscuratula, Heppia obscuratula, Anaptychia obscurata

  Basis for Listing

The range of Heterodermia obscurata (orange-tinted fringe lichen) includes Eurasia and Africa as well as North and South America. In North America, the species is more typical of the eastern United States and the Ozarks, where it appears to be fairly secure if not abundant. Elsewhere in North America the species is known from isolated and widely scattered locations. Heterodermia obscurata was unknown in Minnesota until it was discovered in Cass County in 1976, when a small population was discovered in a cedar swamp near Leech Lake. Since the original discovery of H. obscurata in Minnesota, the species has been documented at two additional locations, both within a few miles of the original discovery site (Northern Minnesota Drift and Lake Plains Section). The Minnesota populations are removed from the nearest population by more than 400 km (250 mi.) and removed from the main range of the species by more than 900 km (600 mi.). Because of its apparent rarity and the disjunct nature of the Minnesota populations, Heterodermia obscurata was designated a species of special concern in 2013.

  Description

Heterodermia obscurata is a foliose (leaf-like) lichen, with a whitish thallus that becomes greenish when wet. The underside lacks a cortex and ranges in color from yellow or orange to white and always has yellow or orange patches. The lobes are typically closely attached to the substrate by simple to branched rhizines. The thallus is sorediate, with soredia forming in labriform soralia at the ends of terminal lobes (Nash et al. 2000).

The most important characteristic for separating H. obscurata from superficially similar species is the presence of the orange to yellow color on the underside of the thallus. Pyxine sorediata (pyxine lichen) is a superficially similar species that occurs in the same habitats as H. obscurata. It has an orange medulla, which can appear to be the lower cortex once removed from its substrate (which can remove the black to whitish lower cortex) and marginal instead of labriform soralia.

  Habitat

In Minnesota, H. obscurata has only been collected in forested peatland communities from the bark of Thuja occidentalis (northern white cedar) trees. All of the known populations are from within 3 km (2 mi.) of Leech Lake, which likely provides an important climate modifying effect for both humidity and temperature. It is likely that the species occurs at other locations within this general area and should be searched for in wet forests as well.

  Biology / Life History

Heterodermia obscurata can reproduce by spores; however, apothecia are extremely rare throughout the species’ range. The vast majority of reproduction in this species likely occurs asexually, through the dispersal of soredia. Soredia are reproductive structures that contain both fungal and algal partners and can be dispersed over short distances.

  Conservation / Management

Loss of habitat is the primary threat to H. obscurata in Minnesota. The most prominent agents of habitat alteration or destruction include logging, housing developments, and environmental changes such as climate change. Any alterations that disrupt the humidity of H. obscurata’s environment would likely have a negative effect on populations of this lichen.

  Best Time to Search

Heterodermia obscurata can be observed year-round, whenever lichens are not covered by snow or ice.

  References and Additional Information

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Moberg, R., and T.H. Nash III. 2002. Heterodermia. Pages 207-219 in T. H. Nash III, B. D. Ryan, C. Gries, and F. Bungartz, editors. Lichen flora of the Greater Sonoran Desert Region. Volume 1. Lichens Unlimited, Arizona State University, Tempe.

Nash III, T. H., B. D. Ryan, C. Gries, and F. Bungartz, editors. 2001. Heterodermia obscurata in Lichen flora of the Greater Sonoran Desert region. Volume 1. Arizona State University Lichen Herbarium, Tempe, Arizona. 532 pp.