New records of Geastrum (Geastrales, Basidiomycota) for the Amazon

ABSTRACT Fungi of the genus Geastrum are known as earthstar fungi, due to the stelliform morphology of their basidiomes. In the Amazon domain, there are 25 catalogued species of Geastrum, with several new records in recent years. Here we report three new species records of Geastrum for the Brazilian Amazon. Geastrum calycicoriaceum and G. rubropusillum were recorded in the southwestern transition zone between Amazon forest and Cerrado savanna. Geastrum calycicoriaceum was recorded for the first time in Brazil.

The genus Geastrum Pers. is characterized by star-shaped (or stelliform) basidiomes and by passive dispersal of spores through a single apical pore, depending on external factors for dispersion (Sunhede 1989).It has a cosmopolitan distribution (Kasuya et al. 2012) and is considered one of the most diverse genera of gasteroid fungi, with 100 to 120 currently valid species worldwide (Zamora et al. 2014).In Brazil, 67 species of Geastrum were recorded in the latest review by Accioly et al. (2019), and 30 species were recorded in the Amazon (Assis et al. 2022).
Publications on gasteroid fungi in the Amazon are still scarce and concentrate around the research poles in the region (Maia et al. 2015), hinting at that there is a large underexplored fungal diversity in this region.Here, we report three new species records from the southwestern Brazilian Amazon.
The taxonomic analysis followed Sunhede (1989), Silva et al. (2014) and Sousa et al. (2014).The macroscopic analysis was conducted by direct visual inspection and under a stereomicroscope.The "Methuen Handbook of Color" color chart (Kornerup and Wanscher 1978) was used for color determination.For microstructure analysis, small portions of ACTA AMAZONICA the specimens were removed and placed on microscope slides containing 3% potassium hydroxide (KOH).The layers were separated using tweezers and then observed under a Nikon Eclipse Ni-U light microscope (LM) with a Nikon DS-Ri1 camera attached (40x and 100x magnification).The size and shape of 30 basidiospores were analyzed and measured under LM and scanned electron microscope (SEM), and checked for the occurrence of apicule and apophysis.The mean ± standard deviation and the ratio between mean height and mean width (Q m ) were calculated.The other microstructures present on the slide were analyzed and measured.
Diagnosis -Geastrum calycicoriaceum is characterized by an ephemeral mycelial layer, which detaches with maturation and forms a calyx or cup under the basidiomes, which gives the species its name (Crous et al. 2020).
Similar species -Geastrum calycicoriaceum morphologically resembles G. velutinum Morgan due to the presence of a yellowish mycelial layer, delimited and fimbriated peristome and the subiculum presence, but G. velutinum differs by the absence of an ephemeral and coriaceous mycelial layer and the lighter colors in the peridium layers (Dissing and Lange 1962).Geastrum argentinum Speg.differs from G. calycicoriaceum by  ACTA AMAZONICA having an undelimited peristome and larger basidiospores (4.8-5.6 mm in diam) (Zamora et al. 2013).
Habit and habitat -Gregarious, growing on decaying wood.
Habit and habitat -Gregarious, growing on decaying wood.
Our records increase the number of known Geastrum species to 28 in the Brazilian Amazon, to 33 in the whole Amazon region, and to 68 in Brazil.The known distribution range of G. rubropusilum is considerably extended south and westwards, while the new localities for G. courtecuissei and G. courtecuissei fit into ranges formed by otherwise widely disjunct occurrence points.Geastrum courtecuissei is recorded for the first time in Brazil.
Geastrum courtecuissei and G. rubropusilum are considered as distinct species within the complex characterized by the presence of hairs on the exoperidium, a critical feature for differentiating species in subsect.Epigaea (Accioly et al. 2019).Geastrum courtecuissei had only been recorded in tropical and subtropical humid forests in Argentina and on Guadalupe Island, in the Caribbean (Accioly et al. 2019) and now is also known in the Amazon region.
As several neotropical species of Geastrum have a very similar morphology, misidentifications have been frequent (Accioly et al. 2019).The genus probably contains a species complex formed by cryptic or semi-cryptic species (Vizzini et al. 2013).When reviewing sect.Myceliostroma, subsect.Epigaea, Accioly et al. (2019) identified six new species that used to be identified as Geastrum hirsutum Baseia & Calonge or G. schweinitzii, demonstrating the hidden diversity within Geastrum in the Neotropics.

Figure 1 .
Figure 1.Location of Mato Grosso state in Brazil, and of the three new species records of Geastrum.This figure is in color in the electronic version.