Synonym: Pannaria crossophylla Tuck., Proc. Am. Acad. Arts & Sci IV: 404. 1860. TYPE: U.S.A. VERMONT. Brattleborough, Russell (FH, lectotype).
The species was transferred to the genus Santessoniella Henssen according to the characters of the thallus (it is semigelatinous, mostly homoiomerous) and the apothecia (biatorine, with hemiamyloid hymenium, I+ red-brown) (Jørgensen 2000, 2005). However, recent phylogenetic studies indicate that the genus is not monophyletic and the type species of it was included in Psoroma (Ekman et al. 2014). Santessoniella crossophylla was not treated in this study and its relationships to other species within Pannariaceae remain unclear.
The species epithet ‘crossophylla’, an unknown word in Latin, may be based on a misreading of Tuckerman’s original label which appears to be ‘crassophylla’ (= thick-leaved), a well chosen epithet (Jørgensen 2000).
Santessoniella crossophylla (Old Gray Crosslobes) is a highly distinctive macrolichen that is endemic to the eastern areas of North America. Previously, populations were known throughout the Appalachian Mountain chain from Vermont and New Hampshire to North Carolina and Georgia, as well disjunct in Canada (Island Anticosti). Unfortunately, it’s historical range has shrunk dramatically in recent decades. At present, the veryfied locations of Santessoniella crossophylla are: (1) in the Ozark Mountains of southern Missouri and northern Arkansas, (2) in the extreme southern Appalachians (especially Great Smoky Mountains National Park), (3) one additional locality in West Virginia, and (4) one locality in Canada, Nova Scotia.
The species was recently searched and not recorded in one of the historical locations (Pennsylvania, Onoko Glen) (Lendemer & Anderson 2008); no information available whether this has been done in other localities of old collections.
As locations in Ozark Mountains and Nova Scotia were recently found, no population size reduction in EOO or AOO can be demonstrated, comparing historial and extant locations. Therefore criteria A and B are not appicable.
Criteria C and D are not applicable as relevant numbers of individuals are not available. Criterion E is not applicable as no quantitative analyses have been carried out.
Conclusion: Santessoniella crossophylla is listed as DD because:
(a) no documantation that the taxon has been searched for in several historical locations (e.g. New Hampshire and Vermont in USA and Island Anticosti in Canada)
(b) the species has not been included in the phylogenetic studies of the family Pannariaceae while an undescribed relative of S. crossophylla was sequenced and analysed; this means that the relationships between the two taxa remain unclear (Ekman et al. 2014) until further studies. New species limitations may also affect the threat status of the taxon/taxa.
Santessoniella crossophylla is distributed in North America, in Canada (Nova Scotia) and USA (see the image above for a distribution map of this species), where it is known from 13 extant populations in the Southern Appalachian Mountains and the Ozark Mountains.
Santessoniella crossophylla is known from 18 populations in the world. Of these, 13 were collected between 1996–2014, with the remaining collected between 1859-1976. Recent field surveys by James Lendemer, Erin Tripp, and Jessi Allen in Great Smoky Mountains National Park (2013-2014) have resulted in the discovery of three small isolated populations. This suggests that the species may be more abundant in the National Park than originally known. Unfortunately, no new populations elsewhere in North America outside of the Smokies or the Ozarks have been discovered.
Population Trend: Decreasing
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.
The biggest threat to Old Gray Crossloabes is loss of suitable habitat and potential disturbance by passing hikers, trail maintenance crews, or other users of the national lands in which this species is found.
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.
The first task, however, is to analyse the phylogenetic relationships between S. crossophylla and its undescribed relative (see Ekman et al. 2014) to ascertain the species limits.
Ekman, S., Wedin, M., Lindblom, L. & Jörgensen, P. M. 2014. Extended phylogeny and revised generic classification of the Pannariaceae (Peltigerales, Ascomycota). The Lichenologist 46(5): 626–656.
Jørgensen, P. M. 2000. Survey of the Lichen Family Pannariaceae on the American Continent, North of Mexico. The Bryologist 103(4): 670–704.
Jørgensen, P. M. 2005. Additions to the Pannariaceae of North America. The Bryologist 108(2): 255–258.
Lendemer, J.C. and F. Anderson. 2008. Santessoniella crossophyllla is rare, but not extinct, in eastern North America. Evansia 25: 74-75.
Lendemer, J.C., R.C. Harris, and E.A. Tripp. 2013. The Lichens and Allied Fungi of Great Smoky Mountains National Park. The New York Botanical Garden Press, Bronx, New York.