Celastrus orbiculatus Thunb.

Raab-Straube, Eckhard von & Raus, Thomas, 2025, Euro + Med-Checklist Notulae, 18, Willdenowia 55 (1), pp. 107-144 : 111-113

Celastrus orbiculatus Thunb. – Fig. 4.

N Bu : Bulgaria : W Rhodope Mts, Smolyan district, along main road from Borino village to Dospat town , between Eshekchidere river and crossroad to Zmeitsa village , 41.66146°N, 24.25736°E, 1262 m, coniferous forest, 27 Oct 2023, Ivanova & Natcheva ( SOM 179185 , SOM 179186 ); ibid., in flower, 18 Jun 2024, Natcheva ( SOM 179209 female individual, SOM 179210 male individual); ibid., with fruits, 17 Oct 2024, Natcheva obs .; S Black Sea coast, Burgas district, along main road between Lozenets village and Tsarevo town, 42.19540°N, 27.81923°E, 20 m, scrubland and rocks on roadside verge, 21 May 2020, Stoyanov ( SOM 178639 female individual, SOM 178640 male individual). – Celastrus orbiculatus is a species new to the Bulgarian flora. During a field trip on 27 October 2023 in the W Rhodope Mts we noticed woody vines with unlobed, ovate, serrate leaves in yellow autumn color, twining on coniferous trees and identified as C. orbiculatus . A search in the herbarium SOM revealed another unpublished collection of this species in flower from the S Black Sea coast floristic region; both male and female plants were collected in the latter place. In Bulgaria, the species invades disturbed sites by roads but also natural forest habitats. In the Rhodope Mts population, the species occupied at least 10 trees of Picea abies ( L.) H. Karst. and Pinus sylvestris L. by the road to a height of more than 7–8 m, or it formed dense canopies over small roadside trees along a c. 700 m section, reaching 15–20 m from the road into the forest. Some stems were cut, followed by sprouting of vigorous regrowth. The site in the Rhodope Mts was revisited in June 2024, and both flowering male and female plants were detected; fruits were observed in October. Although it might be that several neighbouring host trees were occupied by vines of the same clone, the large number of occupied trees situated far from one another suggested a larger number of clones .

The genus Celastrus is not native to Europe. However, two species, C. scandens L. and C. orbiculatus , both widely cultivated commercially for their colourful fruits, are reported as introduced, either naturalized or casual ( Raab-Straube 2018a +). Celastrus orbiculatus is a liana native to temperate E Asia ( China, Korea, Japan, Russian Far East; POWO 2024g). The non-native range comprises Canada, the United States, Vietnam, New Zealand and some European countries ( Beringen & al. 2017; Gudžinskas & al. 2020 and references therein; Mangili & al. 2020; Urziceanu & al. 2020; Mosyakin & Mosyakin 2021; EPPO 2024). Since 2005, the number of newly reported occurrences of this vine is considered to be exponentially increasing in Europe ( Gudžinskas & al. 2020). In its native range, C. orbiculatus grows in thickets on grassy slopes and in mixed forests, in lowlands and mountains ( Zhang & Funston 2008). In its non-native range, the species is highly adaptable, growing under a very wide range of climatic and edaphic conditions ( Del Tredici 2014; Beringen & al. 2017; McKenzie-Gopsill & MacDonald 2021). It clearly benefits from habitat disturbance. The way of introduction of C. orbiculatus in the W Rhodope Mts is unclear and cannot be established unequivocally. It is very unlikely that the species is cultivated as an ornamental plant in the small mountainous villages nearby. It is also unlikely that the species has been deliberately planted against erosion of roadsides in that area. The exact time of introduction is not known either. A plausible means of spread of the Rhodope population is by animals feeding on the fruits and carrying seeds in their gastrointestinal tracts over long distances. For the S Black Sea coast there is evidence to suggest that the species has escaped from the coastal resorts nearby, which have undergone rapid development in the last 30 years, including new construction of many green areas furnished with various ornamental plants; animals likely carried seeds to the coastal rocks where the species was collected in 2020. Celastrus orbiculatus is a successful, competitive invader. Numerous negative impacts of this species have been reported in the invaded areas (see, e.g., Greenberg & al. 2001; Silveri & al. 2001; Williams & Timmins 2003; Ellsworth & al. 2004; Del Tredici 2014; Beringen & al. 2017; Gudžinskas & al. 2020). The species should be regarded as naturalized in Bulgaria because the known populations seem to have persisted for many years without any human intervention. However, the species does not show any invasive behaviour here so far, although it may become locally abundant due to vegetative and seed propagation; suitable habitats for further growth and expansion exist. To our knowledge, the Bulgarian localities are the southeasternmost records of C. orbiculatus in Europe found so far.

D. Ivanova & R. Natcheva