Within the project, we inventoried aphyllophoroid fungi on 16 sampling areas located in eastern Ukraine and covering parts of three administrative regions, namely Kharkiv, Donetsk and Luhansk. All sampling areas are located in the middle basin of Siverskyi Donets River, Black Sea basin and their geomorphology developed due to the erosive activity of the river on the massive Upper Cretaceous sediments. We focused on the inventory of the well-preserved areas. We carried out the inventory in two Nature Reserves, i.e. the most strictly protected areas according to the Ukrainian conservational legislation (3 sampling areas), one National Nature Park (8 sampling areas) and one Regional Landscape Park (one sampling area). Four areas had no protected status but were located close to the protected ones. The list of areas with their definition, short characteristics including protection status, links to the areas as PlutoF objects and visiting/sampling statistics are provided in the Table 1. Beside the text description, each area was captured in photographs viewable on the respective area page in PlutoF (see web links in Table 1)

The sampling areas lie in the East European Plain. The elevation varies between 35 and 220 m a.s.l. The Upper Cretaceous sediments (of a chalk and marl) form a series of hills along the right bank of the Siverskyi Donets River, often with outcroppings. Quaternary sediments were formed mostly on the left bank of the river as alluvial and massive sandy accumulations (Bondarchuk 1959). The soils vary according to the bedrock characteristics. On the products of eolation, the ordinary chernozems with medium humus contents were formed. Slopes of the river valley and ravines are covered with the leached sod-calcareous soils. The river floodplain is dominated by meadow chernozems. Alluvial sand accumulations of the second river terrace bear sod-podzolic soils (Didukh and Pashkevich 2003).

According to the Köppen climate classification, the region falls into the area of a cold forest climate with severe winters and dry, long and hot summers (Jylhä et al. 2010). Compared to the rest of Ukraine, here the climate has the most pronounced continental characteristics. The mean annual temperature is 7.5°С, with recorded minimum of -40°С (January) and maximum of 39°С (July). The average annual precipitation is 400‒540 mm, while the evaporation is 580‒650 mm. Up to 60 days per year with very strong hot dry winds are possible (Popov et al. 1968).

According to the classification of terrestrial ecoregions of the world, the study area belongs to the biome of temperate grasslands, savannahs and shrublands (Olson et al. 2001). It is also known as a steppe region (EEA 2015). In these conditions, the natural woody vegetation mostly represents forest patches of limited size. The few striking exceptions exist due to their proximity to the large Siverskyi Donets River, as well as hilly landscape. Two broadleaf forests (called Teplynska dacha and Maiatska dacha) are the largest forest massifs on the watershed in the Ukrainian steppe zone (Onyshchenko et al. 2007).

The pedunculate oak Quercus robur L. is one of the most important tree species in the area. In the forests on the watershed, this oak species is accompanied by Fraxinus excelsior L., Tilia cordata Mill., Acer platanoides L., A. campestre L., A. tataricum L. and Corylus avellana L. In the Siverskyi Donets floodplain, the oak forest grows mosaically with the forests composed of Alnus glutinosa (L.) Gaertn., various poplars (Populus nigra L., P. alba L. and P. tremula L.), willows (Salix alba L., Salix fragilis L.) and Acer negundo L. (Popovych 1990).

The massive sandy terrace of the Siverskyi Donets River is basically a habitat for the psammophytic grasses and herbs. However, there are numerous depressions which provide a suitable microclimate for the development of the wetland local forests (groves). The usual trees in these habitats are: Betula pendula Roth, B. pubescens Ehrh., Populus tremula, P. nigra and P. alba, Alnus glutinosa and Crataegus spp. The willow shrubby communities of Salix acutifolia Willd. and Salix rosmarinifolia L. are common in some localities (Popovych 1990). As a result of land-use in the 19th and 20th centuries, large areas of the sandy terrace are currently covered not by primary vegetation of psammophytic grasses and herbs, but by plantations of Pinus sylvestris L. However, some of these stands are about 200 years old and resemble natural forests. The true natural pine forests in the region are currently confined to the chalky outcrops with the sod-calcareous soils. These populations were treated in the past decades as a relict species Pinus cretacea Kalen. (Didukh and Pashkevich 2003, Fedorova 1980) currently regarded as a variety of Scots pine, P. sylvestris var. cretacea (Kalen.) Kom. (Gardner 2013).

The work of Alexander Ordynets and Alexander Akulov in eastern Ukraine was supported by the V.N. Karazin Kharkiv National University and Ukrainian Ministry of Education and Science Grant Number 0112U007570/16-16-13 “Biodiversity exploration as a base for the nature conservation network development in Ukraine”. Alexander Ordynets and Ewald Langer were supported by the University of Kassel and the programme LOEWE (“Landes-Offensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz”) of the Hesse's Ministry of Higher Education, Research and Arts within the framework of the Integrative Fungal Research (IPF) project (http://www.integrative-pilzforschung.de). The work of Alexander Ordynets on the molecular identification of Thelephorales was undertaken due to support from the European Social Fund’s Doctoral Studies and Internationalisation Programme DoRa and hosted by the Chair of Mycology, Institute of Ecology and Earth Sciences, University of Tartu, Estonia.

In 16 areas, we sampled living fungal fruitbodiesaccording to the standards for macrofungi collecting (Lodge et al. 2004). We were interested in recording the majority of species from the local species pool. Therefore we sampled not within fixed areas, but covered larger areas by sampling along the forest paths. We were passing up to ten kilometres of forest paths per day. We spent more time at the points which visually harboured higher amounts and diversity of deadwood. Visiting and sampling statistics for each area are provided in Table 1.

If the species could be readily identified in the field, the occurrence was recorded without taking a specimen, i.e. as observation, except for the very first finding of the species during the field work. All fruiting bodies from a single woody substrate or growing in a single cluster on debris or litter were treated as a single individual. For the records on woody substrata (which prevail in the dataset), principal tree fraction, diameter class, decay stage, spatial location and presence/absence of the direct contact with soil were recorded. For all the records, plant species of the substrate as well as characteristics of forest habitat and mesorelief were described (Table 2). All collected data were uploaded and managed on the PlutoF platform (Abarenkov et al. 2010).

One of the challenges in inventorying fungal diversity based on fruiting bodies is the temporal irregularity of fruiting. To reduce the bias associated with this phenomenon, within five years (2007‒2011), we carried out 15 expeditions, usually making one expedition per season (spring, summer and autumn). The earliest and latest sampling dates were March 9 and November 22 respectively. Each expedition lasted as a minimum three and as a maximum seven days. Within a single expedition, we visited up to four sampling areas (see Table 1). Some areas could be visited only once. This may be acceptable in the case of aphyllorphoid fungi which, as opposed to other fruiting fungi, in general create more lasting fruitbodies.

Along with the specimens which were more or less easily identified, there were also collections whose identifications were verified by another expert or collections which we could identify to the genus level only. Wolfgang Dämon, Ivan Zmitrovich, Anton Shyriaev, Heikki Kotiranta, Masoomeh Ghobad-Nejhad, Philomena Bodensteiner, Sergey Volobuev, Viacheslav Spirin and Erast Parmasto kindly helped us in such issues. The names of the experts who verified or improved our identifications are provided in the pane "Identifications", fields "Identifiers" and/or "Remarks" on the respective specimen page as viewed in PlutoF. Additionally, each PlutoF observation linked to our dataset was verified by the platform developer as seen in the pane "Discussion" on the single observation page.

Noticeable specimens were photographed directly in the field or after drying in the laboratory. The micromorphology study of the dried specimens was performed under 1000× magnification using light microscopes Zeiss Primo Star (Carl Zeiss Jena GmbH, Jena, Germany) and Nicon Eclipse 90i (Nikon Corp., Tokyo, Japan). The specimens were examined in 5% aqueous potassium hydroxide solution, Melzer’s reagent and 1% Congo red solution in concentrated ammonia (Ryvarden and Melo 2014). The main identification keys used were Bernicchia and Gorjón (2010), Kõljalg (1996), Larsson (1992), Ryvarden and Melo (2014).

The extent of all sampling areas covers about 180 km in the longitudinal and 60 km in latitudinal direction. The total area of study is 380 km².

48.7175° and 49.29° Latitude; 36.91884° and 39.39385° Longitude.

The dataset contains 3418 species occurrences. It has 2727 specimens and 691 observation records, containing 349 species of fungi from the phylum Basidiomycota. Additional 16 items have no specific epithet but only genus-level (in one case order-level) identification (Table 3).