Assessment Notes

Justification

This species merits ranking as Endangered B2a,b(i,ii,iii,iv,v) based its small area of occupancy (AOO = 96 km² historically, 52 km² currently) coupled with a) severe fragmentation both of remaining natural habitats within the total geographic range of the species and the extant populations outside of  a ca. 1000 km² area of Great Smoky Mountains National Park; and b) continuing decline: extirpation of the species from large areas of its geographic range, as is evidenced by the an absence of relocated historical populations; decline in habitat quality and loss of habitat that has occurred historically and continues to occur, throughout the range of the species; and documented loss of pre-1990 populations (although this is balanced by the discovery of a higher total number of extant populations that are interpreted as new detections of previously existing subpopulations).

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Geographic range

Santessoniella crossophylla (Old Gray Crosslobes) is a distinctive macrolichen that is endemic to the eastern areas of North America (Canada: Quebec, Nova Scotia; US: Arkansas, Illinois, Indiana, Missouri, New Hampshire, New York, North Carolina, Pennsylvania, Tennessee, Vermont, West Virginia) where it is widespread but very rarely encountered. 

Its historical range has shrunk dramatically in recent decades. Santessoniella crossophylla is known from 15 extant populations in the Southern Appalachian Mountains and the Ozark Mountains.

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Population and Trends

Santessoniella crossophylla was originally described from the White Mountains of New Hampshire, and subsequently found at scattered locations throughout the Appalachian Mountains and Ozark Highlands, mostly during the late 19^th and early 20^th centuries. In treating the species, Jørgensen (2000) considered it to be potentially extinct in the wild as he was unaware of any extant populations documented by modern collections. Hinds and Hinds (2007) noted that no extant populations were known from New England, implying that the species was extirpated from that region, but reported several extant populations from the southern Appalachian Mountains and Ozark Highlands. Extensive fieldwork by multiple experts (Pennsylvania: J.C. Lendemer; New England: J.P. Hinds, P.W. Hinds, E. Kneiper, E. Lay; Ontario and Quebec: F. Anderson, J. Gagnon, R.T. McMullin) throughout the northern range of the species has also subsequently failed to relocate historical populations and locate new populations. Lendemer and Anderson (2008) reported the discovery of extant populations in the southern Appalachian Mountains, Ozark Highlands, and a single location in the Canadian Maritimes (Nova Scotia). Subsequent to 2008, extensive inventory efforts in the southern Appalachians have located additional extant populations, all of which are confined to remnant mature, high quality habitats in the north/eastern half of Great Smoky Mountains National Park (NC/TN).

The population in Nova Scotia is here treated as presumed to be extant, however attempts to relocate the species at that location have failed. DNA sequences from the Nova Scotia population were included in published phylogenetic analyses by Ekman et al. (2014) wherein the population was hypothesized to represent a species distinct from Santessoniella crossophylla. Subsequent study (Lendemer et al. in review) with expanded comparative molecular data from four southern Appalachian populations of S. crossophylla confirmed that the Nova Scotia population was 100% identical.

In summary, none of the historical populations of Santessoniella crossophylla have been relocated and the species appears to have been extirpated from large areas of its range (e.g., central Appalachians and New England). Scattered extant populations occur in the Ozark Highlands and Canadian Maritimes, however the majority of extant populations are concentrated within a ca. 1000 km² area of one protected management unit (Great Smoky Mountains National Park). Within this management unit.

Population Trend: Decreasing

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Habitat and Ecology

We suspect that a major correlate of the extreme rarity of Santessoniella crossophylla is its affinity for a very specific habitat type. This species is restricted to the bases of very large overhangs of acidic rock, in environments with a relatively high and constant humidity. Rock overhangs that are too small in size or too shallow (i.e., without sufficient overhang) are not suitable for Old Gray Crosslobes.

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Threats

The primary threat to this species is continued habitat degradation and loss, which could perpetuate the documented historical trends (e.g., Drummond and Loveland 2010, Napton et al. 2010) of extirpation from areas within its geographic range. This includes irreversible alteration of humidity/environmental regimes through natural (e.g., forest composition change from invasive species) and anthropogenic means (e.g., logging, road/utility corridor maintenance/expansion/creation, other forms of resource extraction).

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Conservation Actions

There are currently no conservation activities aimed at protecting or ensuring longevity of any known population of Santessoniella crossophylla.

This species is charismatic and easily recognizable. It would benefit tremendously from four actions: (1) protection of known populations by state or federal means, (2) continued monitoring of known populations for any changes, (3) ecological analyses to more fully understand parameters that restrict its distribution, and (4) more fieldwork across suitable habitat in eastern North America to attempt to document new populations.

While there was some suggestion of the species circumscription (see Ekman et al. 2014), subsequent research has confirmed the taxonomic status of the species (Lendemer et al. 2017).

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Source and Citation

Randlane, T., Tripp, E. & Lendemer, J. 2019. Santessoniella crossophylla. The IUCN Red List of Threatened Species 2019: e.T71622372A71622534. Accessed on 21 November 2025.

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• Country occurrence