Entoloma alnicola Noordel. & Polemis is a saprotrophic mushroom, which was collected once in 2002 on the island of Andros (Cyclades, South Aegean) on wet mossy soil along a stream under Alnus glutinosa and Platanus orientalis. It was described as a new species for science from Noordeloos and Polemis (2008), due to its unique anatomic features. Entoloma alnicola belongs to subgenus Cyanula, stirps Longistriatum, it comes close to E. longistriatum (Peck) Noordel., from which it differs, however, by the rather dark grey-brown tinges in pileus and stipe, a fibrillose-striate stipe surface, the 2-spored basidia and the predominantly utriform or broadly clavate cheilocystidia. Entoloma turci (Bres.) M.M. Moser, which is similarly grey-brown, has a less distinct, non-translucently striate pileus, polished stipe, which frequently turns reddish at the base, 4-spored basidia and differently shaped cheilocystidia. Entoloma scabropelle Noordel. has a fertile lamella edge, and 4- spored basidia.

Entoloma alnicola is endemic to Greece. It was found only once in 2002 (Noordeloos and Polemis 2008) and to date it is only known from its type locality (in stands of Andros). Despite the systematic mycological research and monitoring of alder stands of Andros, E. alnicola has never been collected again for more than 20 years (Polemis et al. 2020). In addition, during the last 5 years, in the frame of a LIFE-NATURE conservation project (“LIFE Andros Park” - www.life-androspark.gr), which focused (among others) on the alder stands of Andros, several systematic forays for alder associated macrofungi were conducted without records of E. alnicola. Apparently, E. alnicola, is a very small mushroom (pileus is not exceeding a diameter of 2 cm, and it requires microscopy to be identified as this species) which can easily be overlooked. However, even considering this, it is believed that even if it is still extant, it is very rare and could have fewer than 50 mature individuals at its type locality. Invoking the precautionary principle, therefore, E. alnicola, is assessed as Critically Endangered under criterion D, but continued, targeted surveying around the type locality and other southern alder stands in Europe is strongly recommended. The possibility of being extinct (PE) has also been calculated by implementing the relevant methodology proposed by IUCN, but resulted that E. alnicola not meeting the conditions for that status yet.

Entoloma alnicola Noordel. & Polemis is possibly endemic to the island of Andros (Cyklades, S. Aegean). It was found only once in 2002, on wet mossy soil with residues of Alnus glutinosa. It has never been collected since in Andros or anywhere in the world, although several surveys were conducted in the following 20 years (Noordeloos and Polemis 2008, Polemis et al. 2020).

Entoloma alnicola is assumed to be associated with Black Alder (Alnus glutinosa), which shows its southernmost limit of its distribution in southeast Europe at Andros island. This species was found once in 2002 and it has never been collected again, although several opportunistic or dedicated surveys were performed in the past 20 years. Moreover, in other countries of continental Europe where alder stands are quite common and several specialised taxonomists on the genus Entoloma are working, this taxon has not been found to date and thus it remains a Greek endemic species. Nevertheless, due to the small size of the basidiomata of this species and the fact it can’t be identified without the aid of a microscope, it is quite reasonable that it may be easily overlooked, still it is considered to be very rare.

Currently, it is estimated that fewer than 50 mature individuals may exist worldwide.

This fungus was recorded growing saprotrophicaly in wet conditions predominantly under Alnus glutinosa and other riparian trees such as Platanus orientalis.

According to European Red List of Habitats - Forests Habitat Group, alder habitats (G1.2a – “Alnus woodland on riparian and upland soils”) and among them the priority habitat 91E0 “Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae)”, have a stable recent trend in quantity in Greece and a decreasing recent trend in quality (for the last 50y). Particularly, as regards to Andros, the degradation of 91E0 Alluvial forests after the devastating flooding events of 2012 is thoroughly documented (Polemis et al. 2020, www.life-androspark.gr). Flooding events are expected to intensify due to the climate change, thus they are considered as the main threat which can cause rapid alterations on the river banks where A. glutinosa occurs, and subsequently to the mycelia of saprobic macofungi such as E. alnicola. Extreme temperatures in conjunction with drought and desertification can also be considered a significant long-term threat for the marginal alder habitats of Andros and Greece in general.

Actions for the restoration of some alluvial alder stands of Andros have taken place in the frame of an environmental LIFE project (http://www.life-androspark.gr). However, restoration actions were not conducted on the alder stands where E. alnicola was collected in 2002.