Rickiella edulis is a South American wood-inhabiting ascomycete, usually found on decaying fallen branches and twigs in the litterfall. Up to now, the fungal species was reported from only four sites: one in Paraguay (Gran Chaco), one in Southern Brazil (Atlantic Forest), and two in Argentina (Gran Chaco and Atlantic Forest) (Romero et al. 2012, Vignale et al. 2015). Moreover, it was believed that the species was locally extinct in Paraguay, since only one collection from 1880 was reported. Recent targeted survey efforts (2023-2024) along its potential distribution in Paraguay and Brazil, coupled with recent records in literature (Trierveiler-Pereira et al. 2020, Hernández Caffot et al. 2023, and other mycologists personal communications), resulted in additional sites and collections, including its rediscovery in Paraguay.
In the previous assessment the species was listed as Endangered - EN (C2a(ii)) because it has rarely been collected. It was assumed that there were over 10,000 mature individuals in the past, and land use changes over the last 100 years have decreased the population to less than 2,000 mature individuals.
With recent data and more information about the species distribution (12 sites from the above mentioned countries and 31 collections), including recent records from Southeastern Brazil (State of São Paulo) and from Jujuy, Argentina (Southern Andean Yungas), we could infer that Rickiella edulis has a total population size of about 3,100 mature individuals, all belonging to a single subpopulation.
These habitats are threatened by human activities, especially the intensification of replacing native forests with exotic tree plantations, intensive agriculture, and clearing for pastures for extensive livestock, as well as urbanization (Izquierdo et al. 2008, Tabarelli et al. 2010, Politi et al. 2021), resulting in a continuous decline of this habitat, including inside protected areas. The loss of required habitat directly threatens this species.
Considering this new calculation of its population size, this species is now assessed as Vulnerable (VU) under criterion C2a(ii).
Rickiella edulis was originally described by Spegazzini (1891) as Peziza edulis. Now this species belongs to the monotypic genus Rickiella (Pfister 1987). Rickiella transiens Sydow, described in 1904 (Sydow in Rick 1904), was considered a synonymy of R. edulis by Pfister (1987).
This is a rare species, having been recorded only for a few localities in South America. Ascomes are large and unmistakable, making this species very conspicuous when the reproductive structures (apothecia) are present.
Rickiella edulis has been recorded from 12 sites (latitudinal range from 22º to 29º S): Southern (States of Rio Grande do Sul and Santa Catarina) and Southeastern (State of São Paulo) Regions of Brazil, Southwestern Paraguay (Department Paraguarí); Central and Northern Argentina (Misiones, Salta and Jujuy). In these areas, we can find three different vegetation types: Atlantic Forest (mainly Seasonal Semideciduous Forest), Grand Chaco (mainly Chaco Umido), and Southern Andean Yungas. The species probably occurs in additional sites within its geographic range where its biotic and abiotic requirements are met.
The species was first recorded in 1891 in Paraguay, growing on dead fallen twigs and logs of unidentified angiosperms among litter, producing large and unmistakable ascomes. Until its last Red List assessment (published on 03 April 2020), R. edulis was known from four localities: one in southern Brazil (Atlantic Forest, Rio Grande do Sul), one in Paraguay (Gran Chaco) and two in Argentina (Gran Chaco, Salta and Atlantic Forest, Misiones) (Romero et al. 2012, Vignale et al. 2015). Recent studies recorded the species in Southeastern Brazil (Atlantic Forest, State of São Paulo) (Trierveiler-Pereira et al. 2020) and Northern Argentina (Southern Andean Yungas, Jujuy) (Hernández Caffot et al. 2023). Moreover, surveys conducted from 2023 to 2024, under a specific project targeting this fungal species (Mohammed bin Zayed Species Conservation Fund 2023 - project #232532246), increased the number of known localities to 12, including its rediscovery in Paraguay. Even though the species ascomes are relatively large and distinctive, and there have been a number of mycological surveys within potential habitats in these three countries, we can assume that the species is rare throughout its range. Before deforestation the species was probably broadly distributed but uncommon.
Deforestation in the Brazilian Atlantic Forest has largely declined over the last two decades. However, historically, it has been heavily exploited, and only 28% of its natural coverage remains, largely composed of forest fragments and secondary forests, usually with less than 10 ha per fragment (Tabarelli et al. 2010, Rezende et al. 2018). Although Misiones is the most preserved fragment of Atlantic Forest in Argentina, However, only ~35%, or ~500,000 ha, of this unique forest is protected in a series of areas that vary in size, adjacency, and degree of protection (DeMatteo 2023).
The Gran Chaco, an extremely threatened biome, suffering from long-term and expanding human occupation and high rates of deforestation (200,000 ha/year) (Gasparri et al. 2008, Gasparri and Grau, 2009, Aide et al. 2013, Volante et al. 2016, Volante and Seghezzo 2018). The native forest in this region is quickly giving way to agricultural activities (Fehlenberg et al. 2017), especially soybeans (Gasparri & Grau 2009, Delvenne et al. 2013).
With about three million hectares currently, 30% of the Southern Andean Yungas in Argentina have been converted to other land uses and the remaining forests have been degraded by unsustainable forestry development and by extensive livestock farming that is not properly managed (Politi et al. 2021).
There are only two records of R. edulis from Paraguay (near Asunción), one from the 19th century (this forest is probably no longer extant), and one from 2024, from a reforestation area. Unfortunately, Paraguay is among the most deforested countries in Latin America (Hansen et al. 2013). The Atlantic Forest is considered one of the most threatened tropical forests and between 1999 and 2016 around 28% of the Atlantic forest was lost in Paraguay (Da Ponte et al. 2017). The area where R. edulis was found encompasses a transition between the Gran Chaco and the Atlantic Forest. From 1945 to 2009, about 74% of the forest coverage was lost in this area (Paveti & Saito 2012). Additional to the loss of forest cover due to the expansion of the agricultural and cattle frontiers, illegal logging, unplanned management of forest extraction, fires, natural phenomena (floods and droughts), and illicit crops are amongst the biggest threats to the species (Miño & Atienza 2017).
The species is expected to be found at 200 sites, resulting in a total estimated population size of about 3,100 mature individuals, all within one subpopulation. This decline results primarily from habitat degradation and the impacts of climate change.
Population Trend: Decreasing
Rickiella edulis is usually found in preserved forest areas, usually along riparian forests and/or areas flooded by rivers, and also in preserved forest fragments in urban areas. It is a saprotrophic species, growing on dead fallen twigs and logs of unidentified angiosperms, usually in an advanced decomposition state. Ascomes are found during the rainy season, usually from November to April (occasionally May).
Rickiella edulis occurs in the Atlantic Forest, Gran Chaco and the Yungas, all of them deforestation hotspots. There are several threats that can lead to habitat loss in unprotected areas, especially the intensification of replacing native forests with exotic tree plantations, intensive agriculture, and clearing for pastures for extensive livestock, as well as urbanization (Izquierdo et al. 2008). The loss of required habitat directly threatens this species. Moreover, climate change alters the rainfall regime, and consequently, affects the production of ascomes. Fire can affect the conservation of this species in several ways, like habitat destruction, soil changes or spore destruction. The increase and prolongation of wildfires in native forest threatens the conservation of this species.
The main action to prevent the further decline of the species is preservation and restoration of its habitat. More surveys are needed to identify other localities and improve knowledge on population trends and ecology. In the same way, national and local protection laws can help the conservation by regulating human activity, promoting conservation programs and others.
More surveys are needed to identify other localities and improve knowledge on population trends and ecology. Since the species is edible, further research about environmental factors (biotic and abiotic) that impacts ascomes production, ex situ production, secondary metabolites and nutritional values of R. edulis could be investigated as well.
Ascomata are edible but with no commercial value.
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