The Pakaraima mountains in Guyana are covered with Amazonian rainforest where Guyanagaster necrorhiza was described, and this are the unique populations known of this species. Considering the climate change scenarios for 2099 where 18% of the Amazonian will be transformed to savanna (Salazar et al., 2007), and the type location is 35 km away from the nearest savanna. Thus, this species should be listed under the A3c criteria due to a expected reduction of 30% in its EOO in the next 100 years. Additionally it fits the criteria B2a as its distribution will be severe fragmented, B2b(ii) as its area of occupancy is estimated to be reduced (B2b(ii)), and B2b(iii) as the habitat quality will be loss.

Genus phylogenetic related with Armillaria (Physalacriaceae) Basidiomata globose to subglobose, with a black verrucose peridium, sequestrate. Gleba with locules and veins pinkish white to brick red. Collumela well-defined light pink to orange red with age. Basidia bi-sterigmate with globose badisiopores without spines (10.8–)12.1–15.8 x 12–15.5(–16.1) µm, and with spines 15.5¬–18.5 x 15.6–18.8(–19.4) µm, dextrinoids. It is associated to Dicymbe corymbosa and D. altsonii (Henkel et al., 2010).

Guyanagaster necrorhiza has high specificity to Dicymbe corymbosa and D. altsonii. These hosts habit the Amazonian rainforest of Pakaraima mountains in Guyana. Just considering climate change scenarios Amazonian rain forest will transform to savanna in 18% for 2099 (Salazar et al., 2007). However, fragmentation and droughts had not been considered in this scenarios, and Amazonian forest is highly threatened by cattle ranching, infrastructure projects and commercial agriculture (McFarland 2018). All populations of this species has been found several times in different years but just in one site of Guyana. This place is 39 km far from savanna biome, so this location have risk to loss its current vegetation.
Thus, this species should be listed under the A3c criteria due to a expected reduction of 30% in its EOO in the next 100 years. Additionally it fits the criteria B2a as its distribution will be severe fragmented, B2b(ii) as its area of occupancy is estimated to be reduced (B2b(ii)), and B2b(iii) as the habitat quality will be loss.

Upper Potaro Basin of Guyana in tropical rainforest (5° 18’ 04.8’’ N, 59° 54’ 40.4’’ W)

The known populations of Guayanagaster necrorhiza were reported around the type location in Upper Potaro basin of Guyana in: Region 8 Potaro-Siparuni-Pakaraima mountains, elevation 710-750 mals in 29-06-2001, 11-06-2002, and 4-07-2003; from 2.5 km southeast of base camp plot 1, 27-07-2008;  2 km southwest of base camp, on roots of fallen Dicymbe corymbosa 22-07-2009; 8 km southeast of base camp at Tadang Creek 24-12-2009; 2 km southwest of base camp, on roots of fallen Dicymbe corymbosa 17-05-2010 (Henkel et al., 2010).
The maps have the type location in blue. I also plotted the distribution of their both hosts, Dicymbe corymbosa and D. altsonii, are the other numerous locations (GBIF Secretariat 2017).

Leaf litter and soil attached to rotten roots of Dicymbe corymbosa and D. altsonii in tropical rainforest, 696 masl

It is highly specific to Dicymbe which growths in Guyana tropical rainforest. Amazon rainforest is highly threatened because climate change: droughts and fragmentation (Staal et al. 2015). Fragmentation in Amazonian forest is driven by economic activities such as cattle ranching, infrastructure projects and commercial agriculture (McFarland 2018). Gaps create understory light availability and drought conditions (Martínez-Ramos et al., 2016), so that fungal species can be vulnerable. This species is not in a protected area, and is 35 km away from a savanna area that would increase in less than 50 years old, according to climate change models (Salazar et al., 2007).

Nowadays the populations of their hosts are not threatened, however Dicymbe genus is ectomycorrhizal host and several species of Amanita, Boletellus, Chalciporus, Clavulina, Cortinarius, Inocybe, Russula, etc. It has been published that the monodominance (host abundance) of these hosts could be the reason of the hyperdiversity of ectomycorrhizal fungi (Alvarez-Manjarrez et al., 2018; Corrales et al., 2018). Thus, Dicymbe should be protected because this site is a fungal hotspot.

This species has been described in 2010 so it could be probable that it has been insufficient sampling in the country, is required to determine whether this species is also in the rest of Brazilian rainforest where D. corymbosa and D. altosonii live.

there are no reports about edibility or use of this species

Alvarez-Manjarrez, J., Garibay-Orijel, R., & Smith, M. E. (2018). Caryophyllales are the main hosts of a unique set of ectomycorrhizal fungi in a Neotropical dry forest. Mycorrhiza, 28(2), 103–115. https://doi.org/10.1007/s00572-017-0807-7

Corrales, A., Henkel, T. W., & Smith, M. E. (2018). Ectomycorrhizal associations in the tropics – biogeography, diversity patterns and ecosystem roles. New Phytologist, 220(4), 1076–1091. https://doi.org/10.1111/nph.15151

Dicymbe altsonii Sandwith in GBIF Secretariat (2017). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2019-05-24.

Dicymbe corymbosa Spruce ex Benth. in GBIF Secretariat (2017). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2019-05-24.

Henkel, T. W., Smith, M. E., & Aime, M. C. (2010). Guyanagaster, a new wood-decaying sequestrate fungal genus related to Armillaria (Physalacriaceae, Agaricales, Basidiomycota). American Journal of Botany, 97(9), 1474–1484. https://doi.org/10.3732/ajb.1000097

Martínez-Ramos, M., Ortiz-Rodríguez, I. A., Piñero, D., Dirzo, R., & Sarukhán, J. (2016). Anthropogenic disturbances jeopardize biodiversity conservation within tropical rainforest reserves. Proceedings of the National Academy of Sciences, 113(19), 5323–5328. https://doi.org/10.1073/pnas.1602893113

McFarland B.J. (2018) The Context of Tropical Rainforest Deforestation and Degradation. In: Conservation of Tropical Rainforests. Palgrave Studies in Environmental Policy and Regulation. Palgrave Macmillan, Cham

Salazar, L. F., Nobre, C. A., & Oyama, M. D. (2007). Climate change consequences on the biome distribution in tropical South America. Geophysical Research Letters, 34(9), 2–7. https://doi.org/10.1029/2007GL029695

Staal, A., Dekker, S. C., Hirota, M., & van Nes, E. H. (2015). Synergistic effects of drought and deforestation on the resilience of the south-eastern Amazon rainforest. Ecological Complexity, 22, 65–75. https://doi.org/10.1016/j.ecocom.2015.01.003