Cytisus sect. Tubocytisus DC. (syn. Chamaecytisus Link) has been a nightmare of European plant taxonomists. There were various and largely conflicting attempts to delimit this group in Eastern Europe, ranging from rather excessive splitting (Kreczetowicz 1940, Skalická 1983, Tzvelev 1987, Fedoronchuk 2019) to overall lumping (Yakovlev and Svyazeva 1984, Majorov 2014). Broader-scale taxonomic treatments (Cristofolini 1991) presented a rather weighted approach, but suffered from an apparent lack of the representative material and type specimens from Eastern Europe. This controversy stemmed from the difficulties in the interpretation of diagnostic characters in this group, infraspecific variability and recent hybridisation between some species. The small scale of morphological differences suggests a close proximity of many taxa in this section, and the presence of numerous polyploid chromosome counts (e.g. Forissier (1973), Parfionaŭ et al. (1975)) indicates that hybridisation played an important role in the creation of its present taxonomic diversity.

Due to the taxonomic uncertainties, the actual distribution of species in Cytisus sect. Tubocytisus is hindered by difficulties in plant identification. This practical trouble leads to the oversimplified representation of the species areas in their distribution maps (e.g. Meusel et al. (1965), Svyazeva and Yakovlev (1986)).

Among the species included in Cytisus sect. Tubocytisus, the C. ratisbonensis Schaeff. group is the most species-rich and taxonomically complicated in Eastern Europe (Tzvelev 1987). In our work on Fabaceae for Atlas Florae Europaeae, a long-term project of large-scale grid mapping of European vascular plants, we have found that the published records and available herbarium collections of this group are not completely reliable; the group required a new taxonomic revision, and the specimens had to be verified and partly re-identified.

We have produced a new taxonomic scheme for the Cytisus ratisbonensis group (Sennikov and Tikhomirov 2024a), which is a further development of the system proposed by Cristofolini (1991). For the first time, we have collected ample data that allow us to assess the morphological characters and to make reliable maps for all accepted taxa in the group in Eastern Europe and adjacent territories. With these data at hand, it was possible to produce IUCN global assessments for the taxa occurring in Eastern Europe. So far, only one species of this group, C. paczoskii V.I.Krecz. (= C. cinereus Host) was assessed as Near Threatened (Sennikov 2017) because of its presumably limited distribution and because of a decline of its habitats. That assessment was based on Didukh (2009) and was considered provisional because of the apparent data deficiency; it is re-assessed here as suggested in the original assessment.

This paper presents a distributional dataset of the Cytisus ratisbonensis group in Eastern Europe and neighbouring countries, with point maps, which aims to provide the background data for Sennikov and Tikhomirov (2024a). The distributional data are collected for Atlas Florae Europaeae, the pan-European grid mapping project (Suominen 1999). This dataset also provides the basis for IUCN assessments of two species involved, which is another objective of the present paper; these make a contribution to the programme of conservation assessments of European endemic shrubs (Wilson et al. 2019).

Study area description

Design description

Sampling description

Quality control

Taxonomic coverage

The study is limited to East European members of the Cytisus ratisbonensis group, which is a group of closely related species of C. sect. Tubocytisus with strictly lateral inflorescences. This group is represented in Eastern Europe by seven species (Fig. 1), namely C. borysthenicus Gruner, C. cinereus Host (syn. C. paczoskii V.I.Krecz.), C. elongatus Waldst. & Kit. (syn. C. lindemannii V.I.Krecz., C. triflorus auct.), C. lithuanicus Gilib., C. polonicus Sennikov & Val.N.Tikhom., C. ruthenicus Fisch. ex Otto and C. wulffii V.I.Krecz.; and by two hybrids, i.e. C. × kreczetoviczii Wissjul. and C. × semerenkoanus Sennikov & Val.N.Tikhom. (= C. czerniaevii auct.). The taxonomy is obtained from Sennikov and Tikhomirov (2024a) and the nomenclature is updated after Sennikov and Tikhomirov (2024b).

Figure 1.  

Photo portraits of species in the Cytisus ratisbonensis group. A C. borysthenicus Gruner (https://www.inaturalist.org/observations/68954267); B C. ratisbonensis Schaeff. (https://www.inaturalist.org/observations/191399034); C Cytisus elongatus Waldst. & Kit. (https://www.inaturalist.org/observations/102192324); D C. cinereus Host (https://www.inaturalist.org/observations/182044044); E C. wulffii V.I.Krecz. (https://www.inaturalist.org/observations/153016459); F C. polonicus Sennikov & Val.N.Tikhom. (https://www.inaturalist.org/observations/115875724); G C. lithuanicus Gilib. (https://www.inaturalist.org/observations/101929175); H C. ruthenicus Fisch. ex Otto (https://www.inaturalist.org/observations/168429147). Photo credits: A A. Efremov; B M. Chytrý; C D. Davydov; D I. Jovanovic; E S. Svirin; F T. Suchan; G D. Tretjakov; H E. Kasandina.

Species distributions

IUCN assessments

Although the study area is formally defined as Eastern Europe, the northern limit of the distribution of the Cytisus ratisbonensis group largely follows the line Minsk – Moscow – Kostroma – Solikamsk.

In the study area, the species of the Cytisus ratisbonensis group inhabit open places in the southern forest, forest steppe and steppe zones, often occurring on sandy soils and among pine forests. Most of the species are confined to plains or hilly areas and rarely can be found in the lower mountain belt (but C. ruthenicus climbs up to 1000 m in the Urals and the Caucasus, and C. wulffii is confined to the mountains in the Crimea and occurs at elevations of 600–1200 m).

Cytisus borysthenicus (Fig. 2) is widely distributed in the forest steppe and steppe regions in Eastern Europe (Ukraine and Russia) and the neighbouring parts of Asia (Kazakhstan), where it is found at minimal elevations. This strictly psammophilous species occurs in sandy steppes and on denudated sands, on alluvial sands along river sides, sometimes in sparse pine forests on sandy soils.

Figure 2.  

Distribution area of Cytisus borysthenicus. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

Cytisus cinereus (Fig. 3) is distributed in hilly lowlands along the north-eastern side of the Carpathians (Poland and Ukraine), together with C. polonicus, and in the Pannonian Plain (Serbia, Hungary, Romania; its presence in Slovakia is expected). It is found in open places, meadows and forest margins, often on sandy or calcareous substrates. The species was reported from Moldova and the neighbouring territories of southern Ukraine (Kreczetowicz 1940, Tzvelev 1987, Shabanova et al. 2014); we have not seen any specimens confirming this occurrence.

Figure 3.  

Distribution area of Cytisus cinereus. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

Cytisus lithuanicus (Fig. 4) was recently resurrected for an octoploid segregate of C. ratisbonensis s.l. (Sennikov and Tikhomirov 2024a). This species is narrowly distributed mostly in the western Polesie, a flatland belonging to Poland, Belarus and Ukraine, and in neighbouring areas. It occurs in margins of dry pine forests, mostly north-east of the distribution area of C. polonicus.

Figure 4.  

Distribution area of Cytisus lithuanicus. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

Cytisus polonicus (Fig. 5) was recently segregated from C. ratisbonensis, from which it differs in smaller calyces and diploid (vs. tetraploid) chromosome number (Sennikov and Tikhomirov 2024a). This species is rather narrowly distributed in hilly lowlands of Poland and Ukraine, largely along the Carpathians. It occurs at low elevations of 200-400 m on open slopes or calcareous denudations and also in pine forests.

Figure 5.  

Distribution area of Cytisus polonicus. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

Cytisus ruthenicus (Fig. 6) is the most widespread and most common species in this group. Its main distribution is centred in the middle and southern parts of the East European Plain, from the Carpathians to the Urals. The species occurs in Poland and Ukraine up to the foothills of the Carpathians; its only verified occurrence in Transcarpathian Ukraine confirms the assumption (Holub and Bertová 1988) that the species should be present also in Slovakia and Hungary. Its occurrence in Moldova assumes its presence in western Romania. In the east, the species distribution includes the southern Urals (with foothills and southern extensions in Russia and Kazakhstan) and the territories along the middle Urals; its easternmost stations are situated in Kurgan Region of Russia and in Qostanay Region of Kazakhstan. In the Crimea, the species occurs mostly along the northern side of the mountains. In the Caucasus, the species is found on the northern side (Russia) and on the southern side, as well as in Transcaucasia (Georgia), where it may occur at elevations of up to 1100 m. The species prefers sparse dry pine forests, shrublands and steppes.

Figure 6.  

Distribution area of Cytisus ruthenicus. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

Cytisus elongatus (Fig. 7) is a thermophilous species which is broadly distributed in Europe and neighbouring Russia. Its core distribution embraces forest steppes of the Podolsk and Dnieper uplands, and other hilly areas and rough terrain over most of Ukraine and neighbouring Moldova and Russia, avoiding the Black Sea lowland. In the west, the species is sparsely distributed in the Carpathians and Balkans, with isolated occurrences in the mountains of northern and central Italy (Cristofolini 1991) and south-eastern France (west of the Rhône River: Tison and de Foucault (2014)). In Asia, the species is nearly confined to the Euxine phytogeographic province as defined by Davis (1985), in Anatolia and the Caucasus, with an extensive presence in the Colchic sector (avoiding the Colchis Lowland) and isolated occurrences in its western part; furthermore, the species was found in the Stavropol Upland. On plains, the species occurs among sparse shrubs in dry creeks, in forest steppes and in oak or pine forests. In mountains, the species is largely confined to lower elevations, but ascends up to 1000-1400 m in Italy and Turkey, with the extreme elevations at 1900 m in the Balkans. In Ukraine, it is frequently found in oak forests and, to a lesser extent, steppe landscapes (Szelag-Sosonko 1987). In the Caucasus, it occurs at elevations below 500(700) m and occupies open slopes and gravelly riverbeds in the areas along the Black Sea; at higher elevations, it is replaced by C. colchicus Albov (Portenier and Solod'ko 2002). In Central Europe, the species occurs in margins and openings of xeric thermophilous oak forests, often on calcareous soils.

Figure 7.  

Distribution area of Cytisus elongatus. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

Cytisus wulffii (Fig. 8) is very narrowly distributed in the mountainous Crimea; its reports from the Western Caucasus (Kreczetowicz 1940, Zernov 2006) are considered erroneous and referable to depauperate individuals of C. elongatus (Sennikov and Tikhomirov 2024a). This species occurs on open rocky slopes in pine forests and mountain meadows, often on calcareous substrates.

Figure 8.  

Distribution area of Cytisus wulffii. Points are based on occurrence records derived from specimens and observations, contours denote the known distribution area.

According to the climate-area interactions, which were uncovered using MaxEnt models created on the basis of complete distribution areas of the species (Table 1), the species of the C. ratisbonensis group can be characterised by their areas and climatic preferences in the following way.

Cytisus borysthenicus may be considered a true xerophyte species, whose distribution is largely confined to the area of European Pontic steppes and forest steppes (Kajtoch et al. 2016). Two species (C. cinereus, C. polonicus) are linked to the area of xeric grasslands of south-eastern Poland and north-western Ukraine (Kajtoch et al. 2016), largely extending to forest steppes of the Pannonian Basin (C. cinereus). Cytisus elongatus can be considered thermophilous and linked to southern types of oak forests. These four species are controlled by temperature parameters, but also are largely dependent on the precipitation regime.

The distributions of two species, C. lithuanicus and C. ruthenicus, are controlled by temperature parameters, but to a lesser extent by precipitation. Their distributions are linked to southern types of pine forests and only to a minor extent overlap with the area of C. elongatus.

These six species have different relationships to the temperature evenness and climatic seasonality. Cytisus cinereus, C. lithuanicus and C. polonicus occur along or within the chain of the Carpathians; these species require a climate featuring lesser seasonal fluctuations in temperature and moisture. On the other hand, C. borysthenicus, C. elongatus and C. ruthenicus have more eastern and southern occurrences; they are less dependent on the climatic evenness and may survive during hot and dry seasons in more arid or continental areas.

Among the floristic elements delimited by Finnie et al. (2007), Cytisus borysthenicus falls within the Dianthus capitatus-element, which is largely congruent with steppic plants. The other species seemingly fall within the Lychnis flos-cuculi element, which is defined broadly to include many plants widely or more narrowly distributed in Central Europe, Balkans and the southern part of Eastern Europe.

Although the species of the C. ratisbonensis group are characterised by rather subtle differences in pubescence, their distributions follow certain phytogeographic and climatic patterns, thus indicating the utility of narrowly defined taxa in plant geography.

We would like to express our deep gratitude to Arto Kurtto (Helsinki) for continuous support and encouragement. V.N. Tikhomirov is grateful to curators of the herbaria which he visited during this work. Sampsa Lommi (Helsinki) produced the maps. Igor Kuzmin (Tyumen), Serena Marner (Oxford) and Vladimir Vasjukov (Togliatti) kindly communicated selected records from their collections. The work of V.N. Tikhomirov was carried out with partial financial support of the State Committee for Science and Technology of the Republic of Belarus (grant Б20СРБГ-010). It was also part of the project 'Comparative studies on critical taxa of the pontic floristic element of Serbia and Belarus' (2020-2021), bilateral cooperation Serbia - Belarus, grant to V.N. Tikhomirov. The work of A.N. Sennikov was performed within the project Atlas Florae Europaeae and received no external funding. Open access is funded by Helsinki University Library.