First record of Hericium flagellum (Basidiomycota) from the “Olbina” nature reserve in Wielkopolska Voivodship, Poland

Hericium flagellum (Scop.) Pers. is considered a rare, wood-decaying fungus that occurs on coniferous trees, predominantly on silver fir (Abies alba). In this paper, a new locality of H. flagellum in Wielkopolska Voivodship is presented, along with the macroand micromorphological features of the collected specimens. Basidiomata of H. flagellum were found in November 2016 and 2017 in the “Olbina” nature reserve (ATPOL Dc-97, Kalisz Forest District), located in a continental mixed coniferous forest close to the northern border of the natural range of silver fir. In 2016, H. flagellum was found growing in the hollow of an old stump of silver fir, and in the following year, this fungus was recorded on a fallen log of silver fir. The implications for conservation are briefly presented. Prospects of further development of the basidiomata of H. flagellum in the “Olbina” reserve are also discussed.


Introduction
Hericium flagellum (Scop.) Pers. (syn. Hericium alpestre Pers.) is one of the four species of the genus Hericium reported from Poland [1], along with H. coralloides (Scop.) Pers., H. erinaceus (Bull.) Pers., and H. cirrhatum (Pers.) Nikol. [syn. Creolophus cirrhatus (Pers.) P. Karst.]. Hericium flagellum is characterized by spherical or irregularly shaped cream-colored basidiomata, up to 30 cm in diameter [2]. Their numerous branches terminate in thin grouped tufts, with pendulous spines that resemble icicles. Usually, H. flagellum produces a single basidioma; however, sometimes several specimens can be found on the same piece of wood. In contrast to other Hericium spp., H. flagellum is found primarily on dead coniferous wood such as logs and stumps. It is rarely found on living trees, and when it is found, it usually appears in tree hollows or trunk wounds. Hericium flagellum is predominately found on silver fir (Abies alba Mill.); thus, its distribution in Poland and other European countries is closely connected with the natural range of this tree. An alternative host tree of H. flagellum is the Norway spruce (Picea abies L. H.Karst) [1][2][3][4]. A record each of H. flagellum is also known from the Swiss stone pine (Pinus cembra L.) and the Siberian fir (Abies pichta) [5]. In Poland, H. flagellum is reported from coniferous and mixed forests with silver fir, e.g., upland mixed fir forest Abietetum polonicum (Dziub. 1928 [7][8][9][10][13][14][15]. Because the distribution of H. flagellum is primarily associated with the natural range of silver fir, this fungus is most frequently recorded in the mountains [7,9,10] and uplands [13,16]. Thus far, H. flagellum has not been reported from the northern part of Poland, despite the presence of numerous mature stands of silver fir growing in the region of Pomerania, outside the native range of this tree [17]. Within the natural range of silver fir in Europe, H. flagellum was also recorded in Austria [18], Bulgaria [19], Croatia [20], France [21], Germany [3,22], Switzerland [2], the Czech Republic [23], Italy [21], Romania [24], Slovakia [25: p. [24][25][26][27][28][29][30][31], Spain [26], and Ukraine [21,27]. Outside the natural range of silver fir, this fungal species was found in the Asiatic area of Russia [5]. In scientific literature, H. flagellum has sometimes been described as Hericium coralloides (Scop. ex Fr.) S. F. Gray. [9,28,29]. Additionally, the macromorphological similarity of the basidiomata of H. flagellum and that of H. corralloides (Scop.) Pers. (found mostly on beech and other deciduous wood), along with the use of the same scientific name with the frequent exclusion of the author's names, has caused problems with their designation to the correct species [24,30]. Moreover, some previous authors did not include information on the substrate preferences of the basidiomata or on their microscopic structure. Finally, if herbarium specimens are in poor condition or missing, reliable verification of data on the distribution of both species is impossible.
In this paper, we describe a new locality of H. flagellum from Wielkopolska Voivodship (western Poland), discovered in the "Olbina" nature reserve during field trips aimed at determining the diversity of macrofungi in continental mixed coniferous forests. To clearly demonstrate that we have positively identified H. flagellum, macro-and micromorphological features of the collected basidiomata are also presented.

Material and methods
Basidiomata of H. flagellum were found in the "Olbina" nature reserve, which was established in 1958 to protect silver fir at the northern limit of its natural range. The first written record concerning this interesting old-growth forest with silver fir in Wielkopolska Voivodship dates back to the interwar period when in 1937 a short description of this forest stand was published [31]. Currently, the "Olbina" reserve covers 16.63 ha within the Kalisz Forest District, near the village of Pieczyska within Kalisz County (ATPOL square Dc-97). The reserve protects the best-preserved patch of continental mixed coniferous forest Festuco ovinae-Pinetum (Juraszek 1928) Kobendza 1930 in Wielkopolska Voivodship, featuring a significant contribution of silver fir [32]. According to the reserve's protection plan, the substantial share of silver fir and spruce in the forest stand makes it floristically similar to the upland mixed fir forest [Abietetum albae Dziub. 1928 = Abietetum polonicum (Dziub. 1928) Br.-Bl. Et Vlieg. 1939]. Additionally, two species characteristic of fir forests are found here: Lycopodium annotinum and Thuidium tamaricinum. The forest stand is dominated by species that are characteristic of coniferous forests (class Vaccinio-Piceetea) [33]. The forest stand of the reserve, aged approximately 176 years, is clearly distinct from the surrounding managed pine forests.
Basidiomata of H. flagellum were found in November 2016 and 2017. The description of the basidiomata morphology is based on the original material sampled in the "Olbina" nature reserve and on the information from the literature [2,21]. The microscopic structures were observed and measured using an Olympus BX53 light microscope (LM) coupled with an Olympus DP26 digital camera. The reported size of the spores, basidia, and gloeocystidia are based on 20-30 measurements. Size ranges of the microscopic features are given as follows: (minimum value-)first decile-ninth decile(-maximum value). Scanning electron microscope (SEM) micrographs were taken using a Zeiss EVO LS10 at the Center for Molecular Biology and Biotechnology, Environmental Testing Laboratory, University of Szczecin (Poland). The specimens were identified by examining their macroscopic and microscopic features and using monographs by Breitenbach and Kräzlin [2] and Bernicchia and Gorjón [21]. The fungal nomenclature and its synonyms follow the description in the Index Fungorum [34] and Species Fungorum [35] databases, and the names of vascular plants follow the description by Mirek et al. [36]. The nomenclature of plant communities was given according to Matuszkiewicz [32]. The collected specimens of H. flagellum were deposited in the Herbarium of the Department of Botany and Nature Conservation, University of Szczecin (SZUB). The occurrence of H. flagellum in Wielkopolska Voivodship is shown on the cartographic map ( Fig. 1) according to the ATPOL grid square system as used by Wojewoda [37].

New locality of Hericium flagellum
Hericium flagellum was first observed in the "Olbina" reserve in early November 2016. A single mature basidioma was found growing in the hollow of an old, broken, rotting silver fir trunk located near an educational trail. The specimen of H. flagellum was approximately 10-12 cm in diameter, cream-white, with numerous branches spreading from a short stalk and terminating in sharp-tufted spines up to 7 mm long. Hericium flagellum was again observed in the reserve in early November 2017, approximately 100 m from the location of the first record. This time, the basidioma grew on a recently fallen, thick log of old silver fir and was much more spectacular: the diameter of the basidioma hidden among branches was approximately 25 cm. The ochre-colored stalk branched repeatedly to form pinkish "twigs" terminating in tufts of long (up to 15 mm), snow-white, pendulous spines (Fig. 2).

Discussion
In spite of its wide distribution range, H. flagellum is regarded as rare [15,26,27,38]. Both in Poland and in many other European countries, this fungus is included on the red lists of fungi and assigned to various threat categories, e.g., E (critically endangered) in Poland [39], EN (endangered) in Bulgaria [40] and Croatia [41], VU (vulnerable) in Austria [18] and Switzerland [42], NT (near threatened) in the Czech Republic [43], R (rare) in Ukraine [27], and "rare" or "near threatened" in Russia, depending on the region [44,45]. In Germany, H. flagellum is ranked as threatened in various threat categories depending on the federal state [46][47][48]. Hericium flagellum is a species proposed for inclusion on the Global Fungal Red List [49]. In Poland, H. flagellum has been protected by law since 1983 [50]; however, since 2014 the species has been under partial protection only [51]. The first critical review of the occurrence of H. flagellum, mostly from the southern part of Poland, was published in 2003 by Wojewoda in the Checklist of Polish larger Basidiomycetes [1]. Afterward, several reports on the occurrence of H. flagellum in Poland have appeared [4,[52][53][54][55][56][57]. Up to now in Wielkopolska Voivodship, H. flagellum has been reported from only once from "Dębno" reserve near Rawicz [58], situated slightly outside the northern limits of the natural range of silver fir. Basidiomata of H. flagellum were found on the deadwood of Scots pine at this location and this is the only published record of H. flagellum on such a substrate. However, the lack of herbarium material from that study (Kubiak 2019, personal communication) does not allow for its verification; therefore, we did not include this finding on the distribution map of H. flagellum in Wielkopolska Voivodship.
Our new records of H. flagellum are an interesting aspect of research on species diversity of fungi associated with silver fir, conducted within our project aiming to determine the diversity of macrofungi in continental mixed coniferous forest [59]. It is worth noting that during mycological research in the "Olbina" reserve, we discovered specimens of another valuable fungal species associated with silver fir, i.e., Hymenochaete cruenta [60], suggesting that the "Olbina" reserve is a local hot-spot of rare fungal species associated with silver fir wood.
The substantial contribution of silver fir in the forest stand of the "Olbina" nature reserve and the significant amount of deadwood in the form of thick logs and trunks provide conditions conducive for the development of additional H. flagellum basidiomata in the future. The exceptional shape and size of the basidiomata of this species draws the attention of forest visitors. Although the fungus is edible, the basidiomata are not attractive to mushroom-pickers because there is no tradition to picking H. flagellum for household consumption. Additionally, H. flagellum is protected by law. Therefore, occurrences of H. flagellum in the "Olbina" reserve seem not to be threatened.