Introduction. Poisonous plants in urban environments pose a threat to humans and animals. Incidents of poisoning by weeds, wild plants, as well as those used in landscape design have been reported. In Germany, for example, between 2001 and 2010, approximately 13,000 incidents were recorded, with children accounting for 85% of victims [1]. According to the American Association of Poison Control Centers, from 2000 to 2008, plants were responsible for 3.4% of all poisonings in the United States, and children under the age of six accounted for almost 70% of cases [2]. The analysis of various Poison Control Centers in Australia, Germany [3], Morocco [4], New Zealand [5], Thailand [6], and the United Kingdom found that plant exposure was the cause of 1.8–8% of all referrals [7]. In most cases, significant intoxication was not recorded, but there were reports of severe and life-threatening poisoning. The risk of poisoning in urban areas remains high. A study of the urban flora in Hong Kong revealed 26 species of poisonous plants, which were associated with 65 cases of poisoning ranging in severity from 2003 to 2017 [8]. The flora in Novi Sad (Serbia) included 22 species of poisonous plants, and the authors [9] noted their dangerous proximity to children's institutions.

Poisonous plants are those that, when touched or ingested, can cause harm or even death. They also include plants that may cause a toxic or fatal reaction [10].

Poisonous plants are related to allergenic plants, which have been previously studied in Rostov-on-Don [11]. While allergenic plants can cause allergies, poisonous ones can be much more dangerous.

According to statistics, more than 15,000 cases of poisoning from poisonous plants are reported annually in Russia. Typically, plant toxins affect the body through the digestive system, eyes, and skin. Of these cases, 80% involve children under the age of six [12].

The analysis of literary sources has revealed a lack of knowledge about the distribution and species composition of poisonous plants in cities of the Russian Federation. The most comprehensive information is available for Saratov. The authors [13] mention 46 species of poisonous plants from 29 families found within the city. Poisonous flora of Voronezh, Buinaksk, and Makhachkala has also been studied insufficiently and separately [14].

Poisonous plants in Rostov-on-Don have not been studied specifically. There is little information available about the Lower Don region [15].

The aim of the presented work was to assess the potential threat posed by poisonous plants growing in Rostov-on-Don.

Materials and Methods. The species of poisonous vascular plants in Rostov-on-Don were studied. The primary data was collected by the route method during field work in 2023–2024.

The toxicity class of plants was determined in accordance with the modified classification proposed by A. Filmer [16].

– A — strong toxic effect, may cause serious illness or death;

– B — minor toxic effect, vomiting or diarrhea occurs if the plant is swallowed;

– C — effect is caused by oxalate crystals (irritation of the mouth, tongue and throat, can lead to swelling of the throat, difficulty breathing, burning pain and upset stomach);

– D — juice or thorns can cause skin rash or irritation.

Rostov-on-Don has a temperate continental climate with mild winters and hot, dry summers. According to long-term weather observations, the average air temperature is +11.0°C. January is the coldest month with an average temperature of –2.0°C, and July is the warmest month with an average of +23.4°C. The annual average precipitation in Rostov-on-Don is 618 millimeters. The surrounding vegetation is mainly steppe [17].

Results. As a result of research in Rostov-on-Don, 66 species of poisonous vascular plants belonging to 23 orders of flowering plants have been identified. According to D.V. Vakhnenko [18], the entire flora of the Rostov urban agglomeration consisted of 848 species. Thus, the share of registered toxic flora species was about 8% of the total number of species of the Rostov flora.

The order Ranunculales was found to be the largest, with 14 toxic plant species (21%). The order Solanaceae included 6 species (9%). The Asparagales order was in third place (5 species, 8%). The remaining 20 orders were relatively small and included from 1 to 4 species.

According to Ya.M. Golovanov [19], 67 species of poisonous plants were found in the flora of the city of Meleuz (Bashkortostan), which was close to the Rostov number.

For comparison, the flora of poisonous plants in Saratov was 30% smaller than in Rostov. It had 46 species [13]. Obviously, the greater diversity was due to the Rostov climate, which was more favorable for plants such as Hedera helix, Toxicodendron radicans, Wisteria sinensis, etc. They were often used in landscape design.

The studied toxic flora included various families, some of which were not typical for this region (Phytolaccaceae, Anacardiaceae, Hydrangeaceae). Most of the poisonous plants belonged to the Ranunculaceae and Solanaceae families, which was expected, as representatives of these families were generally toxic to varying degrees. Most of the poisonous plants in Rostov-on-Don were represented by 1–2 species. The intraspecific diversity of the toxic flora was very heterogeneous, since cultural forms also belonged to poisonous ones. Ornamental crops such as Hosta, Hydrangea, and Paeonia had a significant number of varieties, but all of them contained certain toxic substances.

Table 1 provides a complete list of poisonous plants found in Rostov-on-Don.

Rostov-on-Don ecological and cenotic analysis of the flora of poisonous plants shows the relationship of some species with certain types of habitats and cenoses (Fig. 1).

Most poisonous plants were found in flower beds and parterres, that is, in communities of ornamental herbaceous plants (Flower garden) — 27 species (41% of the total number of species). Twenty species (30%) were associated with Ruderal cenoses. Thirteen species (20%) were found in the Residential areas. The least number of species was included in urban dendrocenoses — 6 species (9%).

The resulting distribution was quite natural, considering that artificial communities of flower beds and parterres included a diverse range of plants. However, planning elements of landscape design and green construction did not take into account the risks of poisoning by poisonous ornamental plants. For example, representatives of the buttercup family from the genera Anemone and Aquilegia contain alkaloids and glycosides that are dangerous to life and health, yet they are very popular among flower growers.

Many poisonous plants belonged to the group of ruderals. They grew in littered, unkempt territories, on roadsides, wastelands, etc. Ruderal poisonous plants were characterized by high rates of reproduction, quickly capturing new habitats, that is, they were powerful and uncontrolled sources of toxic substances. The group included such deadly species as poison hemlock (Conium maculatum), black henbane (Hyasciamus niger), European birthwort (Aristolochia clemetitis), and others.

Poisonous plants of residential areas were, as a rule, single specimens or group plantings in the private sector or elements of phytodesign on the territory of residential complexes. With an unqualified selection of the species, only decorative characteristics of the planting material were considered. However, such plants were quite dangerous, even in small numbers.

In recent decades, the American pokeweed (Phytolacca americana) has become widespread in southern Russia, including Rostov-on-Don. Pokeweed is native to North America, but the species is widespread on the Eurasian continent. The decorative qualities of pokeweed have caused it to be cultivated in different countries, and as a result, local ecosystems have suffered from another invasive species. Pokeweed has negatively affected the biocenoses of South Korea [20] and Italy [21]. It spreads due to its unpretentiousness, ability to grow rapidly and reproduce by producing large numbers of seeds. All parts of pokeweed, including attractive berries, contain saponins and alkaloids [22], which can cause serious poisoning when ingested by humans and animals.

Biomorphological analysis of the toxic flora of Rostov-on-Don revealed the predominance of perennial grasses. These included 30 plant species (45% of the total number of studied species). 14 species (21%) of poisonous plants were annual. Shrubs and trees came in third place with 15 species (23%). Lianas and biennials were also found among the poisonous plants, the proportion of which did not exceed the total number of species. The resulting distribution was expected and reflected the proportion of life forms in the flora of the Rostov-on-Don agglomeration, where perennial grasses also predominated, and shrubs and trees were represented in smaller numbers [18]. It is worth noting that the largest number of poisonous plants belonged specifically to families with a predominance of herbaceous forms (Ranunculaceae, Solanaceae). A similar distribution of biomorphs was observed in the toxic flora of Saratov, where perennial grasses and shrubs also played a significant role [13].

Toxicity classes reflect the degree of danger of a particular species to humans and animals (Fig. 2).

Some types combined the properties of two classes. As an example, Hedera helix and Hedera colchica ivies were climbing, evergreen vines that were increasingly used in private gardening (Fig. 3). The juice of these plants could cause burns and skin irritation (Class D), and when ingested, ivy caused gastrointestinal disorders (Class B).

Most of the identified poisonous plant species did not have a significant toxic effect, although their use could lead to gastrointestinal discomfort. There were 42 such species, accounting for 64% of all identified species. Of these, 16 caused irritation or skin damage, and were therefore classified as Class D. Plants with the most severe toxic effect from Class A included 21 species (32%). Only one species from Class C was identified (Maclura pomifera). The use of these plants threatened calcium oxalate poisoning with edema of the upper gastrointestinal tract and respiratory organs. Maclura pomifera was rare, but was found in private landscaping. It was chosen because of the interesting shape of its fruits.

Let us focus on ragweed (Ambrosia artemisiifolia) separately. Its allergenic activity in Rostov-on-Don was previously discussed [11]. Some authors pointed to toxic substances in all parts of ragweed, which could lead to negative consequences for the body [23].

Some species, often found in ruderal habitats, had an unconfirmed hazard status, i.e. there was no consensus on their toxicity. These were, for example, Schleicher fumitory (Fumaria schleicheri), chickweed (Stellaria media), and roadside pepperweed (Lepidium ruderale) [19].

The toxicity of plants in all identified cases was due to the presence of alkaloids — 28 species (42% of the total number of species), glycosides — 17 species (26%), saponins — 5 species (7%) and other toxic compounds.

Accessible and attractive plants with noticeable, bright fruits are dangerous (especially for children). In Rostov-on-Don, 14 such species were found (21% of the total number of species). They belonged to the toxicity class B, as a rule, they did not give an acute toxic effect, but they could cause moderate poisoning. Examples included Parthenocissus sp. [24] and Symphoricarpos albus [25].

Discussion and Conclusion. It is necessary to educate the population of Rostov-on-Don about the possible dangers of plants used for landscaping.

The scientific research described in this article revealed the presence of poisonous plants throughout the city. A significant proportion of these plants were found to be associated with ruderal habitats, where they grow freely and are easily accessible to humans and animals. Additionally, the diversity of toxic flora in urban environments is increasing due to the introduction of ornamental grasses and shrubs that contain dangerous compounds. These findings should be taken into consideration in landscape design projects to ensure the safety of both humans and wildlife.

The study of poisonous flora for the cities of southern Russia has been conducted for the first time. It is planned to study the quantitative characteristics of urban plant communities with toxic species. The data collected will be used to develop recommendations for landscaping and landscape design.