Cladonia subsetacea has an area of occupancy of less than 300 km2, with a plausible AOO of up to 900 km2, and populations have been severely fragmented by agricultural and urban/suburban development. Its asexual reproductive strategy probably strongly limits its dispersal to nearby habitat patches. It is threatened by further loss of habitat and lack of natural disturbance regimes sustaining its required open sand microhabitat. Over the last 90 years, significant declines in area of occupancy and numbers of individuals are the result of habitat conversion, and remaining subpopulations are threatened by declines in quality of habitat due to fire suppression. A recent study shows that Cladonia perforata, which is living in the same habitat type and areas has been declining in the last decade and will continue to do so, if the natural disturbance regime is not recovered or emulated (Herron et al., 2025). From this information we infer a habitat and population decline for C. subsetacea.

Cladonia subsetacea is restricted to a small area of occupancy in fossil sand dunes in the southeastern Coastal Plain of the USA with a small number of subpoulations found on open sandstone and granite outcrops and one record from Cuba. Across its range, subpopulations on these areas of relatively well-drained high ground have been fragmented by recent and ongoing intense pressure for urban/suburban and agricultural development, and a majority of remaining subpopulations suffer from declines in habitat quality because of a lack of natural fire disturbance.

Cladonia subsetacea is a vagrant lichen, restricted to well-drained, open-sand habitats, and rarely open rock outcrops, in the Coastal Plain of the United States. One specimen is known from the Peninsula Corrientes in Cuba. The bulk of its known occurrences are in the fossil sand dune systems in Florida, and high pine habitats in South and North Carolina, with smaller numbers of occurrences in Georgia and two historic collections from Alabama and Virginia. The AOO is calculated to be approximately 232 km2. The two areas where C. subsetacea is most abundant, sand dune habitats in Florida and North and South Carolina, are frequently visited and well-studied, therefore most of the occurrences there are probably known. The areas with the isolated occurrences are probably less well explored concerning this species, and there could be existing subpopulations that are not recorded. The extent to which this lichen occurs in Cuba is unknown. We suspect that suitable habitat is limited, since persisting populations need live elevated from sea level to avoid being flooded, and these places are sought-after for housing. We thus suspect that AOO could be two to three times larger than presented here due to less sampling effort in parts of the species’ range and its unknown state in Cuba.
Habitat patches of this species are often separated by kilometers of unsuitable habitat, which is limiting to dispersal. This limitation is further exacerbated by the suspected very small dispersal distance of this species – it reproduces by fragmentation of the thallus and thus dispersal kernels (branches/parts of the thallus) are very large and probably very immobile. We infer severe fragmentation from this information, since more than half of the individuals are separated from other habitat patches by a large distance relative to the travel distance of the dispersal kernels.
Considering the small AOO, severe fragmentation and the continuing decline (see below: Population and Trends), C. subsetacea triggers the threshold for VU under criterion B2 and will continue to do so, even if many more subpopulations are found.

This lichen can be locally abundant, but subpopulations are limited in spatial extent by the limited occurrence of open sand microhabitats within white sand scrub, and by the fragmentation and loss of naturally patchy scrub habitats due to urban and agricultural development. Very few open sand habitats remain undeveloped in the southeast Coastal Plain. A recent study on Cladonia perforata, which occupies the same habitat type and is often found together with C. subsetacea, shows that improper fire management has led to a decline in abundance from 2011 to 2024, since subpopulations often cannot recover from consuming fires (Herron et al., 2025). Because of the considerable amount of common sites, and because it is not known that C. subsetacea has a better fire resistance than C. perforata, we infer that C. subsetacea populations have declined in the last 15 years too, and will continue to do so if not managed otherwise.

Cladonia subsetacea is a vagrant lichen, restricted to well-drained, open-sand habitats in the southeastern Coastal Plain of the United States. It is limited to the bare sand gaps between plants on extremely well-drained, nutrient poor sandy soils. These gaps are maintained by a combination of periodic fire, nutrient limitations, and potentially cryptogamic crusts, which limit the establishment of vascular plants. Fire return intervals are from 2-10 years in sandhills, and up to 100 or more years in rosemary scrub. Fire return intervals which are too long for each type of habitat result in the accumulation of litter, which has the dual effect of adding nutrients and covering bare sand soil. The nature of these soils means that they are extremely desirable for commercial citrus farming and urban/suburban development.

The habitat of this species is under intense pressure from housing development and is subject to lack of proper management in the absence of natural fire regimes, allowing its required microhabitat of bare sand patches to be overgrown with vascular plants. The lack of proper fire management is also increasing the risk of severe fire, which subpopulations may not be able to survive. Rising sea levels pose a threat to this species, since a significant proportion of subpopulations are located at very low elevation. Research shows that Cladonia species in the mid-Atlantic coast face a significant loss of both range (14-36% for 0.3 m to 1.8 m sea level rise) and climatically suitable area (Allen & Lendemer, 2016). This applies to the northern part of the range of C. subsetacea. Several populations of C. perforata, which is occupying the same habitat as C. subsetacea, have been extirpated by hurricanes, so we infer that hurricanes are also a threat for C. subsetacea.

This species is not listed regionally, nationally or internationally. However, around 50% of the occurrences in Florida are in conservation lands, which are federal, state, local, and private managed areas.

The available data on this species allows for a statement on AOO and EOO, with some uncertainty. No population data is available for this species and estimating population size and trends is currently not possible, so further research is needed to acquire information regarding population size. Surveying in suitable habitats in Alabama, Virginia and Georgia is needed to determine the status of the species in these fewer sampled areas.