Bacidia gullahgeechee is a crustose lichen with a granular leprose thallus that grows on the trunks of palm trees along the Atlantic Coast of southeastern North America. The AOO is 32 km2 and the population is considered to be severally fragmented by urbanization and coastal development. These factors combined with climate change related impacts have resulted in a continuing observed decline in the area, extent and quality of habitat. The declines in the number of mature individuals are inferred from the decline in population due to loss of host trees and suitable habitat. For these reasons the species is assessed as endangered under criteria B2a,b(ii, iii, v)

Bacidia gullahgeechee is a crustose lichen with a granular leprose thallus that resembles B. lutescens but differs chemistry and ecologically (Lendemer 2018). The species epithet is a tribute to the Gullah Geechee people in the coastal regions of South Carolina, Georgia, and Florida in the United States. The naming honors the cultural heritage and geographical connection to the habitats where this lichen species is found, highlighting the importance of local communities and their environments in scientific discourse and taxonomy.

Bacidia gullahgeechee is found almost entirely in the Ashepoo, Combahee, and Edisto Basin (commonly referred to as the “ACE Basin”; see NOAA 1992) in the Mid-Atlantic Coastal Plain of south-eastern North America. It is also known from two occurrences in Florida, also located in the Coastal Plain of southeastern North America. Extensive fieldwork and inventories for lichens have been carried out across the region where Bacidia gullahgeechee occurs, as well as more generally throughout the Mid-Atlantic Coastal Plain and broader Coastal Plain, over a span of more than three decades (1980-2016; see Lendemer et al. 2016, Lendemer 2018). Despite large-scale intensive inventories, focused on coastal maritime forest habitats and inconspicuous microlichen species, B. gullahgeechee remains known only from eight sites.

The species has an EOO of 27,445 km2 and AOO of 32 km2. The small AOO of Bacidia gullahgeechee, in part, likely reflects the naturally restricted distribution of the mature coastal maritime forest habitat that is primarily occupied by the species. It also reflects the fragmentation of this habitat type due to the rapid, large-scale development (industrial, residential, recreational) and urbanization of coastal areas in South Carolina. The fragmentation of what were historically connected and contiguous areas of coastal maritime forest has resulted in severe fragmentation of the population of B. gullahgeechee. A continuing decline in the number of mature individuals is inferred based on the loss of host trees from continuing development of areas occupied by the species. While population demographic studies and long-term monitoring of the species have not been carried out, the unique habitat and ecology suggest that the overall population has decreased, is decreasing, and will decrease in the future, due to the loss of suitable habitat and host trees as a direct result of coastal erosion of barrier islands, sea-level rise and increased intensity/frequency of storms. As is the case for development, these factors are also inferred be resulting in a corresponding ongoing decline in the number of individuals. The impacts of coastal erosion and sea-level rise in particular on the population of this species are evident at sites in the ACE Basin, such as Hunting Island and Pockoy Island, where mature maritime forests and host trees of B. gullahgeechee are actively eroded along the coastal edge of the barrier islands.

Bacidia gullahgeechee is known from eight sites that constitute six locations. Two of these sites are located in Florida, are separated spatially and disjunct from the core range of the species in South Carolina. Each of the two Florida sites constitutes a single location as the species is unlikely to be extirpated from both by a single event (e.g., wildfire, hurricane or storm flooding). The six sites in South Carolina are grouped in four locations of coastal maritime forest that are spatially separated (>10 km apart) and separated by major, unconnected, waterways such that a single event (e.g., wildfire, hurricane or storm surge) is unlikely to extirpate the species from more than one location.

Bacidia gullahgeechee grows abundantly on both the trunks and woody petioles of Sabal palmetto, commonly known as palmetto or Sabal palm (Lendemer 2018). It is restricted to this substrate and extensive studies have been carried out that would have detected it on other locally co-occurring substrates (Lendemer et al. 2016, Lendemer 2018). With the exception of the two sites in Florida, which are from low lying swamp forests, the species is entirely restricted to a subset of mature coastal maritime hardwood forests in South Carolina. These forests only develop on the oldest, most stable dunes of barrier islands (Bellis 1995).

 

The primary threats to Bacidia gullahgeechee are habitat loss and degradation due to urbanization and development, which have severely fragmented the main habitat occupied by the species and by extension have rendered the population severely fragmented and restricted to six locations (see e.g., Jones et al. 2013, Napton et al. 2010). Climate change is synergistic with these threats exacerbating the decline in habitat and population as a result of increasing frequency of extreme weather events, sea-level rise and coastal erosion (Allen & Lendemer 2016). Additionally, air pollution from areas of coastal industry and urbanization is a likely threat to the species given the absence of the species on host trees in urban areas of greater Charleston and Georgetown, South Carolina.

Conservation actions for Bacidia gullahgeechee should focus on habitat protection, restoration, and management, targeting its narrow range of habitat and substrate. Implementing legal protections and conservation agreements, along with raising public awareness, are essential. Collaborative efforts among stakeholders, including researchers, land managers, and local communities, are vital for the effective conservation of this potentially endangered species.

Comprehensive research for Bacidia gullahgeechee lichen should prioritize extensive fieldwork and inventories across the Mid-Atlantic Coastal Plain and the broader Coastal Plain, including Florida, to verify its distribution. Given its limited known occurrences and habitat specificity, population assessments are needed to understand its conservation status. Additionally, detailed habitat analyses, genetic studies, and threat assessments are essential to inform effective conservation strategies. By addressing these research priorities, we can better understand and protect this potentially endangered species and its habitat.

The species is collected by scientists for use in research and biodiversity documentation.