First record of Sphaerobolus stellatus Tode (Basidiomycota, Geastraceae) from the Amazon, Brazil

Sphaerobolus stellatus Tode is a fascinating gasteroid fungus that is distinguished from other fungi by the diminutive morphology of the starry basidiome when mature and its peculiar strategy of spore’s dispersion. This taxon ejects the gleba for a considerable distance as if it was cannon, and therefore is popularly known as artillery fungus. Although the species is cosmopolitan, records are seldom in regions such as South America, and many of them require greater attention due to the absence of important morphological characters. In Brazil, the South American country with most records, the distribution was restricted to a few sites, none of them in the Amazon. This study describes the occurrence of S. stellatus from the Amazon, contributing to the understanding of its geographical distribution and making the material available for future diversity studies.

The genus Sphaerobolus Tode (Geastraceae) was described almost 300 years ago by Micheli (1729), who at the time named it Carpobolus. However, the currently accepted name was coined by Tode (1970) when he adequately described the type species. The generic name is derived from the Greek words "sphaer" meaning "sphere" and "obolus" meaning "to throw", i.e. ball-throwing fungus or artillery fungus due to its peculiar ability to eject its gleba at a considerable distance to disperse its spores (Walker, 1927;Bottomley, 1948;Geml, Davis & Geiser, 2005a;Brantley, Davis & Kuhns, 2001).
The genus diversity is a source of great discussion in the scientific community and the information available is divergent. In the fungal database Index Fungorum (Cabi, 2021) there are 35 taxon, from which only four species are recognized (S. brunneocarneus Rick, S. stellatus Tode, S. ingoldii Geml, D.D. Davis & Geiser e S. minimus Sacc.). The others are synonymized with S. stellatus, the type species, not validated or transferred to other genera. On the other hand, Geml, Davis & Geiser (2005a, b), based on morphological data, molecular analyses and characteristics of mycelial cultures, recognized only three species (S. iowensis L.B. Walker, S. ingoldii e S. stellatus), even though their study was concentrated in materials from the northern hemisphere, despite its cosmopolitan nature (Geml, Davis & Geiser, 2005b).
The species S. stellatus is the best supported in the clade, present in all continents, except for Antarctica (Geml, Davis & Geiser, 2005b). In South America, information is scarce i i and part of the few existing records require review and molecular studies for elucidation as documented by Hosaka et al. (2020), mainly for the material lacking essential morphological characters in integrative taxonomy. In Brazil, where the most extensive tropical forests in the world are home to great biological diversity (Lewinsohn & Prado, 2005), about 50% of samples (n=34) were not identified at the species level and the remaining samples were divided between S. stellatus (88%) and S. stellatus var. brasiliensis Viégas & C.G. Teixeira (12%) (Cria 2021), even though the latter was synonymized with the first (Cabi, 2021). The literature on gasteroid fungi in the country reports S. brunneocarneus and S. stellatus (Rick, 1961;Treiveiler-Pereira et al., 2009), but if you consider the study of Geml, Davis & Geiser (2005b), only the latter would be documented.
The scenario is even more concerning in the Amazon, where the richness of fauna and flora stands out, but little is known about funga (only 1050 species were known until 2015 according to Maia et al. 2015). Even though the number of fungal species has increased in recent years, studies on gasteroid mycobiota are still emerging. Thus, in order to contribute for the knowledge on the diversity of Amazonian fungi, we describe the first record of S. stellatus from the Amazon; expanding and improving the understanding of its distribution and contributing for future diversity studies.
The collections were carried out in 2018 in a fragment of the Amazon forest in western Pará, Brazil (2°48'41.9"S, 54°18'11.8"W), near the Silvio Pinto (Curuá-Una) Hydroelectric power plant. The forest fragment is about 30,000 ha large and is mostly a plateau area (with little altitudinal variation) covered by high-canopy forest and its understory dominated by natural regeneration, herbaceous and shrubby plants, palm trees and shrubs.
The current distribution of S. stellatus in South America is still restricted to a few localities and although in Brazil there are the highest number of records, the distribution was known only in the states of Rio Grande do Sul (Rick, 1961;Treiveiler-Pereira et al., 2009;Treiveiler-Pereira, 2018), São Paulo (Bononi, Trufem & Grandi, 1981;Treiveiler-Pereira et al., 2009), Rio Grande do Norte (Oliveira, 2019), Pernambuco and Santa Catarina (Cria, 2021). This is the first record from the Brazilian Amazon, as well as from the state of Pará.
Many samples deposited in South American scientific collections require greater attention to verify species identification. In part, due to the lack of materials with important characteristics normally necessary to describe a gasteroid fungus, such as Sphaerobolus, which gleba and basidiospores are important morphological characters for the genus. However, these characters can be difficult to observe depending on the basidiome's degree of maturation, when found. Thus, especially in these cases, molecular studies are necessary in view of the divergence regarding genus diversity, as highlighted by Hosaka et al. (2020), and it is possible that the diversity of the taxon is greater than that recorded so far. This is the first record of S. stellatus from the Brazilian Amazon and in light of your example, it is necessary to assess areas little or not at all explored in the Amazon, where there is great fungal diversity. However, the difficult access to some sites, and the decharacterization of the forest by deforestation, concern scientific and conservation efforts and are obstacles to research involving large-scale mycology. Thus, this study increases the geographical distribution of S. stellatus to the Amazon and contributes to minimize the knowledge gap on fungal diversity in this worldwide important area.