Distribution and preliminary assessment of a rare fungus Hemileccinum depilatum (Boletales, Basidiomycota) in Ukraine

Hemileccinum depilatum (Boletales, Basidiomycota) is currently known from Western and Central Europe, the Mediterranean, the Balkan Peninsula, and Asia (Azerbaijan and Turkey). The fungus is rare throughout its range and is included in the Red Lists in several European countries. In Ukraine, the species is known since 2006. Formerly, H. depilatum was found on the South Coast of Crimea, in the Mountain Crimea, Western Forest-Steppe and the Carpathians. The species was recorded only in five localities in three regions of Ukraine: Khmelnytsky, Transcarpathian, and the Autonomous Republic of Crimea. Over the recent years, the fungus has been also reported from the following five regions: Cherkasy, Ivano-Frankivsk, Kyiv, Lviv, and Ternopil. Thus, by now the total number of the species localities increased from 5 to 14. However, the number of records grows due to additional data recently provided from field observations by amateur mycologists, rather than it can be considered as a result of an increasing population trend of the fungus. Undoubtedly, H. depilatum is a rarely occurring species in Ukraine and is to be protected. A preliminary assessment of the species at the national level using the IUCN criteria and categories is provided. Today, the main threat to its existence is collection of the fruit bodies by local population. Therefore, it is proposed to continue searching for new localities of the fungus and to protect those sites at least at the regional level, as well as to provide public outreach, primarily through social networks, which nowadays bring together tens of thousands of amateur mycologists in Ukraine.

In Ukraine, until recently only one species of this genus was known, H. impolitum, a quite widespread mushroom commonly gathered in forests by local population. It has been recorded in Central Polissya, West, Right Bank and Left Bank Forest-Steppe, Left Bank Grass-Meadow and Grass Steppe, as well as Crimea (Zerova et al., 1979;Akulov, Prydiuk, 2007;Sarkina, 2018). The second species, H. depilatum, was found for the first time in Ukraine by I.S. Sarkina (2014a, b) in 2006 in Mys Martian Nature Reserve (South Coast of Crimea). The second and third finds of the fungus in 2008 were reported by the first author from Western Forest-Steppe (Heluta, 2012). After that, H. depilatum was recorded in the Mountain Crimea (Sarkina, 2014b) and the Carpathians (Berkela, Pokynchereda, 2015;Gleb, 2016). In 2016, a single fruit body collected in Central Polissya was brought by amateurs to the M.G. Kholodny Institute of Botany, NAS of Ukraine, for identification. Since recently, more observation data on the occurrence of this species have been provided through "Fungi of Ukraine", a social network group (https://www.facebook.com/groups/ Hryby.Ukrayiny/?ref=bookmarks).
Consequently, distribution area of the fungus in the country was expanded to include the Right Bank Forest-Steppe, as well as several new localities were added to the earlier reported regions mentioned above.
Here we provide a description and illustrations of H. depilatum (Fig. 1), followed by a list of all currently known localities in Ukraine and a distribution map (Fig. 2). ( Pileus 4-10(-15) cm wide, hemisphaerical, later convex, plano-convex to flattened cushion-shaped, surface uneven, slightly wrinkled or pitted, mostly glabrous, but at early stages finely tomentose in pits and at pileus margin, later completely glabrous, at first yellow-brown, then chestnut-brown, fading to ochre or tinged to flesh color (Fig. 1, A-D). Pileipellis nonseparable. In young fruit bodies pileipellis is composed of two layers, the upper soft trichoderm consisting of loosely intertwined filamentous hyphae and the lower layer formed by dense somewhat saddle-shaped hyphae. Soon after, as the upper layer starts to disappear, the lower one becomes a pseudoepithelium composed of ellipsoid to subglobose cells (Fig. 1, F). Hymenophore near stipe apex slightly depressed, sometimes almost free. Tubes up to (10-)15-20 mm long, deep yellow when young, olive-yellow with age. Pores minute, 0.5-1 mm in diameter, rounded, concolorous with the tubes, unchanging when bruised. Stipe 6-15 × 2.5-4(-4.5) cm, relatively fleshy, elongate clavate or elongate subfusoid, tapering, occasionally spindleshaped toward base, often distinctly curved, covered with scabrosities as in Leccinum, but less conspicuous, light-colored and not darkening, later partly collapsing; stipe surface light-yellow or whitish, in old fruit bodies sometimes with brownish to burgundy spots or reddish band. Stipe base covered with white or whitish, occasionally yellow-olive to brownish tangled basal tomentum. Partial veil and annulus absent. Context of stipe and pileus whitish, light-yellow, often more deep yellow above tubes and under stipe surface, at stipe base or all over the stipe in old fruit bodies sometimes with brown or brown-red spots (Fig. 1, E), or completely red-brown (Fig. 1, C), color unchanging when cut, odor unpleasant resembling iodoform, particularly in the lower part of the stipe, taste mild.
Hemileccinum depilatum in its general appearance is quite similar to H. impolitum but differs in pitted, or hammered, pileus surface and microscopic structure of pileipellis. In H. impolitum, pileipellis hyphae are cylindrical and filamentous, with only a small number of terminal cells slightly broadened at the top. In H. depilatum, pileus surface undergoes conspicuous changes during its development. Initially, the pileipellis consists of two layers, the upper layer of loosely intervowen filamentous hyphae and the lower one with densely arranged hyphae. At this stage, the pileus surface appears finely tomentose. However, it becomes completely glabrous, as soon as the filamentous hyphae in the upper layer disappear. In the originally lower layer, gradually broadening hyphae become more or less inflated, so that the pileipellis eventually is composed of predominantly ellipsoid to subglobose cells. Thus the two species can be easily distinguished by this micromorphological character.
Hitherto, H. depilatum was recorded in Central Polissya, Western and Right Bank Forest-Steppe, Carpathian Forests, Mountain Crimea and Southern Crimea. According to administrative divisions in Ukraine, the species was reported from the Autonomous Republic of Crimea, Cherkasy, Ivano-Frankivsk, Kyiv, Khmelnytsky, Lviv, Ternopil and Transcarpathian regions. At present, in total 14 localities of the fungus are known in the country. However, the number of records increased due to additional data recently provided by amateur mycologists as a result of their field observations, rather than growing population trend of the fungus. Undoubtedly, H. depilatum is a rarely encountered species which is to be protected at the national level. It has been already recommended to include this species into the Red Data Book of Ukraine (Heluta, 2012). However, it is necessary to assess its conservation status nationally.
Nowadays, the red-listing system developed by the IUCN is widely internationally recognized (IUCN…, 2012). This system is based on assessing conservation status of all species against standard criteria applied to estimate extinction risk for the species and to assign it to one of the recommended categories (IUCN…, 2019). We have made a preliminary evaluation of the status of H. depilatum in Ukraine using the IUCN Red List categories and criteria, in accordance with special guidelines for fungal red-listing (Dahlberg, Mueller, 2011). This is a tentative assessment since the species was only recently recognized in the country (in 2006), therefore due to insufficient recording time for an ectomycorrhizal fungus, its population size cannot yet be estimated. However, based on the concept of functional individual (Dahlberg, Mueller, 2011) and current distribution of the fungus in the country, we can apply criterion D for its evaluation. The number of mature individuals in the known up to now 14 localities can be estimated as minimum 140, but maximum actual number of the localities can be increased in future, apparently not exceeding 100. Thus, for the time being the species is assessed as Vulnerable (VU) under criterion D1.
At present, the main threat for H. depilatum is collecting its fruit bodies by local population. Therefore for conservation purposes it is important to protect already known sites, at least at the regional/local level, and to continue searching for new localities of the fungus in appropriate habitats. It is also essential to raise public awareness and to engage local people, primarily through social networks connecting professional mycologists with tens of thousands of amateurs.