Stojanović et al. 2025, Biologica Nyssana 16(1) 75 16 (1) June 2025: 75-91 DOI: 10.46793/BiolNyss.16.1.7S Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Original Article Jovana Stojanović University of Niš, Faculty of Sciences and Mathematics, Department of Biology and Ecology, Višegradska 33, 18 000 Niš, Serbia jovanagreen6@gmail.com (corresponding author) Bojan Zlatković University of Niš, Faculty of Sciences and Mathematics, Department of Biology and Ecology, Višegradska 33, 18 000 Niš, Serbia Dragana Jenačković Gocić University of Niš, Faculty of Sciences and Mathematics, Department of Biology and Ecology, Višegradska 33, 18 000 Niš, Serbia Branko Jotić University of Niš, Faculty of Sciences and Mathematics, Department of Biology and Ecology, Višegradska 33, 18 000 Niš, Serbia Marina Jušković University of Niš, Faculty of Sciences and Mathematics, Department of Biology and Ecology, Višegradska 33, 18 000 Niš, Serbia Received: October 28, 2024 Revised: February 15, 2025 Accepted: February 19, 2025 Abstract: The flora of rock outcrops in the Stara Planina Mountains (Serbia) was analyzed to assess its diversity, as well as its biological and chorological spectra. A total of 125 vascular plant species, representing 75 genera and 35 families, were identified. The dominant families were Poaceae, Caryophyllaceae, and Asteraceae, while Asplenium and Sedum were the most species-rich genera. Hemicryptophytes (48.8%) and chamaephytes (31.2%) were the predominant life forms, well-adapted to harsh rocky environments. The dominance of taxa from the Eurasian Mountain (32%) and Eurasian (16%) area types reflects the montane-continental and temperate-continental climate characteristic of the study area. Furthermore, the presence of glacial relict species highlights the role of high-altitude rocky habitats as microclimatic refugia, offering long- term protection against adverse climatic changes. This study underscores the substantial floristic diversity and biogeographical significance of rocky habitats in this part of the Stara Planina Mts. Key words: chasmophytes, the Stara Planina Mts., biological spectrum, chorological spectrum, floristic diversity Apstrakt: Floristički diverzitet stenovitih staništa Stare planine u Srbiji Flora stenovitih staništa Stare planine (Srbija) proučavana je sa ciljem utvrđivanja njenog diverziteta, biološkog i horološkog spektra. Ukupno je identifikovano 125 vrsta vaskularnih biljaka iz 35 familija i 75 rodova. Poaceae, Caryophyllaceae i Asteraceae su dominantne familije, a Asplenium i Sedum najzastupljeniji rodovi. Hemikriptofite (48,8%) i hamefite (31,2%) predstavljaju dominantne životne forme, prilagođene stenovitim staništima. Dominacija taksona koji pripadaju Evroazijsko planinskom (32%) i Evroazijskom (16%) areal tipu ukazuje na planinsko-kontinentalni i umereno- kontinentalni tip klime, koji su karakteristični za istraživano područje. Takođe, prisustvo glacijalnih reliktnih vrsta potvrđuje da stenovita staništa visokoplaninskih regiona imaju ulogu mikroklimatskih refugijuma, pružajući dugoročnu zaštitu od nepovoljnih klimatskih promena. Ovo istraživanje ukazuje na znatan floristički diverzitet i biogeografski značaj stenovitih staništa ovog dela Stare planine. Ključne reči: hazmofite, Stara Planina, biološki spektar, horološki spektar, floristički diverzitet Introduction Due to their inaccessibility, rock outcrops are among the best-preserved terrestrial environments, providing refuge from grazing, competition, fire, anthropogenic pressures, and climatic changes (Larson et al., 2000). The floristic composition of vegetation on these outcrops is shaped by geological and geomorphological characteristics (e.g., bedrock composition, structural heterogeneity, eluvial processes, and erosion), topographic features (e.g., exposure and slope), and microclimatic conditions (e.g., water availability, temperature, and insolation). In general, floristic diversity on rock outcrops tends to increase with higher humidity, greater rock stability, and an increased availability of space for seed germination (Larson et al., 2000). Chasmophytes are highly specialized plants adapted to endure the harsh conditions of the rock fissures they inhabit. Many have evolved structural adaptations, such as bulbs, succulent leaves, aerial roots, vegetation mats (which facilitate the growth of other plants), and resurrection traits (Ribeiro et al., 2007). Chasmophytes share several functional © 2025 Stojanović et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and build upon your work non-commercially under the same license as the original. 76 traits: they are predominantly long-lived perennials, typically woody at the base, with an extended flowering period, high seed germination rates, and various mechanisms for long-distance seed dispersal (Panitsa & Kontopanou, 2017). The presence of vertical cliffs and rock outcrops leads to the fragmentation and isolation of open habitats, which support both endemic species and those at the edge of their distribution range (Juvan et al., 2011; Gwitira et al., 2013; Gentili et al., 2015; Zhao & Gong, 2015; Cutts et al., 2019; García et al., 2020). There is a strong link between chasmophyte ecology and endemism, as most endemic species are chasmophytes (Panitsa & Kontopanou, 2017). The occurrence of relict species within chasmophytic communities suggests that rock outcrops function as refugia from rapid climatic changes, allowing vegetation to persist as long as the rock remains intact (Larson et al., 2000). These habitats support plant populations with highly stable demographic dynamics and low extinction risks (Larson et al., 1999; Picó & Riba, 2002; García, 2003), as well as slow-growing, stable communities in a climax stage. Although scattered records of species from the rocky habitats of the Stara Planina Mts. in Serbia exist in older literature (Pančić, 1884; Adamović, 1908-1911; Josifović, 1970-1977), these habitats have remained largely understudied until recently. While recent studies have examined rock outcrop vegetation - such as those by Ranđelović et al. (2000, 2021) in Serbia and Szokala (2023) in Bulgaria - no comprehensive research has specifically addressed the floristic diversity, life-form spectra, or biogeographical patterns of the rock outcrop flora in this mountain range. This study represents the first detailed investigation of the diversity, biological spectra, and chorological patterns of rock outcrop flora in the Serbian part of the Stara Planina Mts. By filling this knowledge gap, our research enhances the broader understanding of biodiversity patterns and species specialization within these unique ecosystems. Materials and Methods The sampling area was discontinuous, covering only localities with rock outcrops that support chasmophytic communities (Fig. 1), within the smaller western part of the Stara Planina Mts. in Serbia. The study area is bounded by the Beli Timok, Trgoviški Timok, and Visočica rivers, as well as BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fig. 1. Map of sampling localities (1 - Babin zub Peak; 2 - Crvene stene Peak; 3 - Midžor Peak; 4 - Pečka klisura Gorge; 5 - Gorge between the villages of Topli Do and Temska; 6 - Ponor Plateau; 7 - Rosomački vrh Peak; 8 - Rosomačka reka Gorge; 9 - Tumba Viewpoint; 10 - Kovani dol Gorge; 11 - Tri Čuke Peak; 12 - Tupanar Peak; 13 - Babin zub Viewpoint; 14 - Visočica River Gorge; and 15 - Žarkova čuka Peak) 77 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia the border with Bulgaria. Geologically, it is divided into northern pre-Permian formations and southern Permian to Cretaceous sediments (Lakušić & Ćetković, 2007). Soils on siliceous rock outcrops include silicate Lithosols, Regosols, and Rankers, while calcareous rocks support calcaric Leptosol. Terrain variation creates diverse microclimates: the foothills have a temperate-continental climate with semi-dry summers and mild winters, whereas higher altitudes experience a montane-continental climate with long, cold winters. January temperatures range from -5.3 °C to 3.7 °C, and July temperatures from 11.8 °C to 28.8 °C (Milovanović, 2010). Precipitation during the growing season varies between 300 and 360 mm, peaking in May and June (Lakušić & Ćetković, 2007). The vertical vegetation profile of the Stara Planina Mts. includes oak (300- 1100 m a.s.l.), beech (1100-1500 m a.s.l.), Norway spruce (1500-1750 m a.s.l.), subalpine (1750-1900 m a.s.l.), and alpine (above 1900 m a.s.l.) altitudinal belts, with the timberline around 1550-1600 m a.s.l. (Ranđelović et al., 2019). Field research was conducted from June to September 2023, focusing on the flora of rock outcrops. Collected specimens were deposited at the Herbarium Moesiacum Niš (HMN). Plant material was identified using the dichotomous keys of Tutin et al. (1964-1980), Josifović (1970-1977), Sarić (1992), and Sarić & Diklić (1986). Nomenclature follows the Euro+Med PlantBase (2006+), except for Asplenium × alternifolium Wulfen (Niketić & Tomović, 2018), while classification aligns with WFO. Plant life forms were determined following Mueller- Dombois & Ellenberg (1974), with adaptations for the flora of Serbia by Stevanović (1992a). Taxa were classified into six life forms: phanerophytes (P), chamaephytes (Ch), hemicryptophytes (H), geophytes (G), therophytes (T), and scandentophytes (S). Chorotypes were identified according to Meusel et al. (1965, 1978) and Meusel & Jäger (1992), as modified for Serbia by Stevanović (1992b). Taxa were categorized into the following area types: Arctic-Alpine (AA), Boreal (BOR), Central European (CE), Cosmopolitan (COSM), Eurasian (EA), Eurasian Mountain (EAM), Holarctic (HOL), Mediterranean-sub-Mediterranean (MED-SMED), and Pontic (PONT). Results and discussion A total of 125 vascular plant species, belonging to 35 families and 75 genera, were identified on the rock outcrops of the Stara Planina Mts. in Serbia (Tab. 1). Although rock outcrops host less than 10% of the total taxa reported for the vascular flora of the Stara Planina Mts. in Serbia (1,742 taxa) by Lakušić & Ćetković (2007), they display remarkable floristic diversity, especially considering the limited area Table 1. List of recorded vascular plants on the rock outcrops of the Stara Planina Mts. (Serbia), including their life forms, area types, recorded localities, and bedrock types on which they were observed. Abbreviations for life forms: Phanerophytes (P), Chamaephytes (Ch), Hemicryptophytes (H), Geophytes (G), Therophytes (T), and Scandentophytes (S). Abbreviations for area types: Arctic-Alpine (AA), Boreal (BOR), Central European (CE), Cosmopolitan (COSM), Eurasian (EA), Eurasian Mountain (EAM), Holarctic (HOL), Mediterranean-sub-Mediterranean (MED-SMED), and Pontic (PONT). Locality numbers correspond to those in Fig. 1. In the bedrock type column, 'S' indicates siliceous rocks, 'L' indicates limestone, and 'S/L' indicates both. For species found on both types of bedrock, the predominant type is bolded; if both types are equally represented, neither is bolded Taxa Life form Area type Locality Bedrock type POLYPODIOPHYTA Fam: Aspleniaceae Asplenium adiantum-nigrum L. Ch COSM 9, 10 S Asplenium ceterach L. Ch EA 4, 8 L Asplenium ruta-muraria L. Ch HOL 1, 4, 5, 7, 8, 13, 14 S/L Asplenium septentrionale (L.) Hoffm. Ch HOL 2, 9, 10, 13, 15 S Asplenium trichomanes L. Ch COSM 1, 2, 5, 8, 9, 10, 12, 15 S/L Asplenium viride Huds. Ch BOR 1, 3, 6, 12 S Asplenium × alternifolium Wulfen Ch HOL 15 S Fam: Cystopteridaceae Cystopteris fragilis (L.) Bernh. Ch COSM 1, 3, 5, 6, 8, 12, 14, 15 S/L 78 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fam. Dryopteridaceae Dryopteris expansa (C.Presl) Fraser-Jenk. & Jermy Ch BOR 1, 11 S Dryopteris filix-mas (L.) Schott Ch HOL 1 S Fam. Ophioglossaceae Botrychium lunaria (L.) Sw. G BOR 3 S Fam. Polypodiaceae Polypodium vulgare L. Ch HOL 1, 5 S Fam. Woodsiaceae Woodsia alpina (Bolton) Gray Ch AA 15 S PINOPHYTA Fam. Cupressaceae Juniperus communis subsp. nana Syme P BOR 1 S ANGIOSPERMS Fam. Amaryllidaceae Allium carinatum L. G MED- SMED 3 S Allium carinatum subsp. pulchellum (G.Don) Bonnier & Layens G MED- SMED 15 S Allium flavum L. G MED- SMED 2, 5, 7 S/L Allium schoenoprasum L. subsp. schoenoprasum G HOL 15 S Fam. Apiaceae Angelica sylvestris L. H BOR 1 S Seseli libanotis (L.) W.D.J.Koch H EA 1 S Fam. Araliaceae Hedera helix L. S CE 8 L Fam. Asparagaceae Muscari comosum (L.) Mill. G EA 9 S Ornithogalum kochii Parl. G MED- SMED 3, 13, 15 S Fam. Asteraceae Anthemis cretica subsp. carpatica (Willd.) Grierson Ch EAM 1, 13 S Aster alpinus L. H AA 1 S Centaurea stoebe subsp. australis (A.Kern.) Greuter H PONT 9 S Centaurea stoebe subsp. serbica (Prodan) Ochsmann H PONT 15 S Cicerbita muralis (L.) Wallr. H EA 8 L Hieracium bifidum Hornem. H BOR 1 S Leontodon crispus Vill. H MED- SMED 2 S Leucanthemum graminifolium (L.) Lam. H EAM 12 S 79 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Pilosella alpicola (Hoppe) F.W.Schultz & Sch. Bip. H CE 9 S Pilosella hoppeana (Schult.) F.W.Schultz & Sch. Bip. H EAM 1 S Senecio rupestris Waldst. & Kit. H EAM 13 S Solidago virgaurea L. H/G HOL 9 S Fam. Brassicaceae Arabis alpina subsp. caucasica (Willd.) Briq. H EAM 7 L Arabis sagittata (Bertol.) DC. H EA 5 S Aurinia saxatilis subsp. orientalis (Ard.) T.R.Dudley Ch MED- SMED 5 L Draba doerfleri Wettst. H EAM 1 S Draba lasiocarpa Rochel H EAM 4 L Rorippa lippizensis (Wulfen) Rchb. H EAM 15 S Fam. Campanulaceae Campanula rapunculoides L. H EA 14 L Campanula rotundifolia L. H HOL 1 S Campanula sparsa Friv. T CE 9 S Campanula wanneri Rochel H EAM 1, 3, 5, 12, 13, 15 S Fam. Caryophyllaceae Arenaria serpyllifolia L. T EA 4 L Cerastium alpinum L. Ch AA 3, 12 S Cerastium banaticum (Rochel) Heuff. Ch MED- SMED 15 S Dianthus moesiacus Vis. & Pančić H EAM 15 S Dianthus petraeus Waldst. & Kit. subsp. petraeus Ch EAM 7 L Heliosperma pusillum (Waldst. & Kit.) Rchb. subsp. pusillum Ch EAM 1, 3, 12 S Minuartia verna (L.) Hiern Ch EA 7, 12 S/L Petrorhagia prolifera (L.) P.W.Ball & Heywood T MED- SMED 2 S Petrorhagia saxifraga (L.) Link Ch MED- SMED 4, 5 L Scleranthus perennis L. Ch EAM 13 S Silene flavescens Waldst. & Kit. Ch EAM 4, 5, 14 L Silene lerchenfeldiana Baumg. Ch EAM 1, 9, 11, 13 S Silene viscaria (L.) Jess. H EA 5, 9 S Fam. Crassulaceae Jovibarba heuffelii (Schott) Á.Löve & D.Löve Ch EAM 1, 15 S Sedum album L. Ch EAM 2, 5, 7, 8, 10, 15 S/L Sedum alpestre Vill. Ch EAM 3, 12 S Sedum annuum L. T AA 1, 2, 9, 12, 13, 15 S Sedum cepaea L. T MED- SMED 9 S 80 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Sedum dasyphyllum L. Ch MED- SMED 8, 10 S/L Sedum hispanicum L. H/T MED- SMED 2, 4 S/L Sedum ochroleucum Chaix Ch MED- SMED 7 L Sempervivum marmoreum Griseb Ch EAM 3, 4, 15 S/L Fam. Cyperaceae Carex kitaibeliana Bech. H EAM 15 S Carex sempervirens Vill. H EAM 3, 12 S Fam. Ericaceae Vaccinium myrtillus L. Ch BOR 1 S Fam. Gentianaceae Gentiana asclepiadea L. H EAM 1 S Fam. Geraniaceae Geranium lucidum L. T EA 5 S Geranium macrorrhizum L. G EA 1 S Geranium purpureum Vill. T MED- SMED 8, 14 L Geranium rotundifolium L. T EA 4 L Fam. Hypericaceae Hypericum maculatum Crantz H EAM 1, 12 S Fam. Juncaceae Juncus trifidus L. H AA 3, 11, 12 S Luzula luzuloides (Lam.) Dandy & Wilmott H CE 1 S Luzula spicata (L.) DC. H AA 3 S Fam. Lamiaceae Clinopodium alpinum (L.) Kuntze Ch EA 2, 4, 15 S/L Lamium garganicum L. H MED- SMED 1, 13 S Satureja kitaibelii Wierzb. ex Heuff. Ch MED- SMED 4 L Stachys recta L. H EA 2 S Thymus praecox subsp. jankae (Čelak.) Jalas Ch MED- SMED 1, 3, 13, 15 S Thymus praecox subsp. polytrichus (A.Kern. ex Borbás) Jalas Ch EAM 1, 15 S Fam. Orobanchaceae Euphrasia pectinata Ten. T EA 15 S Fam. Oxalidaceae Oxalis acetosella L. G EA 1 S Fam. Plantaginaceae Plantago holosteum Scop. H MED- SMED 15 S Veronica barrelieri Roem. & Schult. H EAM 15 S 81 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fam. Poaceae Agrostis capillaris L. H HOL 1 S Anisantha sterilis (L.) Nevski T HOL 2 S Avenella flexuosa (L.) Drejer H HOL 9, 11 S Bellardiochloa variegata (Lam.) Kerguélen H EAM 11, 12 S Festuca dalmatica (Hack.) K.Richt. H PONT 1, 11, 12, 13 S Festuca ovina subsp. supina (Schur) Oborny H EA 1, 3, 11, 12 S Festuca panciciana (Hack.) K.Richt H EAM 1, 7, 11, 13, 15 S/L Festuca picturata Pils H CE 12 S Festuca rubra L. s.l. H HOL 12 S Melica transsilvanica Schur H EA 2, 4 S/L Poa alpina L. H AA 3, 15 S Poa badensis Haenke ex Willd. H EAM 7, 15 S/L Poa laxa Haenke H EAM 1 S Poa nemoralis L. H HOL 1, 2, 5, 9, 10, 13 S Sesleria coerulans Friv. H EAM 1, 3, 12 S Sesleria filifolia Hoppe H EAM 7 L Fam. Polygonaceae Rumex acetosella L. H HOL 9 S Fam. Primulaceae Primula minima L. H EAM 3, 12 S Fam. Ranunculaceae Clematis vitalba L. S CE 10 S Ranunculus montanus Willd. H EAM 1 S Thalictrum aquilegiifolium L. H CE 1 S Fam. Rosaceae Drymocallis rupestris (L.) Soják H CE 15 S Rubus geniculatus Kaltenb. P CE 9 S Fam. Rubiaceae Asperula purpurea (L.) Ehrend. Ch EAM 4 L Galium album Mill. H CE 5 L Galium anisophyllon Vill. H EAM 4 L Galium lucidum All. H MED- SMED 7 L Galium odoratum (L.) Scop. H EA 1 S Fam. Saxifragaceae Saxifraga bryoides L. Ch EAM 3 S Saxifraga moschata Wulfen Ch EAM 3, 12 S Saxifraga paniculata Mill. Ch AA 1, 3, 7, 12, 15 S/L Saxifraga pedemontana subsp. cymosa Engl. Ch EAM 1, 3 S Saxifraga rotundifolia L. H EAM 1, 5, 12 S Saxifraga tridactylites L. T EA 3, 8, 10, 12 S/L 82 they occupy. Moreover, several species documented in this study, such as Poa laxa Haenke (Niketić et al., 2023), Festuca picturata Pils, Rubus geniculatus Kaltenb., and Draba doerfleri Wettst., are new records for the region, suggesting that the floristic diversity of the Stara Planina Mts. is greater than previously recognized. However, it is important to note that the local endemic chasmophyte Campanula calycialata V. Randjel. & Zlatković was not observed during the study, as expected, since it is considered extinct (Ranđelović et al., 2019). The phylum Polypodiophyta comprises six families, six genera, and 13 species, accounting for 10.4% of the total taxa recorded in the study area. The phylum Pinophyta consists of a single family, represented by one species (0.8%). Angiosperms are the most diverse, encompassing 28 families, 68 genera, and 111 species, constituting 88.8% of the total taxa identified. The dominant vascular plant families are Poaceae Barnhart, Caryophyllaceae Juss., and Asteraceae Giseke, represented by 16, 13, and 12 species, respectively (Fig. 2), accounting for 12.8%, 10.4%, and 9.6% of the total species recorded. Asplenium L. and Sedum L. are the dominant genera, each contributing 5.6% of the total species, followed by Saxifraga L. at 4.8% (Fig. 2). Certain genera, such as Asplenium among ferns and Sedum among herbaceous vascular plants, exhibit notable consistency in their global distribution on rock outcrops (Larson et al., 2000). Desiccation-tolerant plants, particularly poikilohydric species such as Asplenium ruta-muraria L., A. ceterach L. (Sádlo & Chytrý, 2009), and succulent xerophytes from the genera Sempervivum L. and Sedum (Oettli, 1905; Lüth, 1993), are prevalent in these habitats. Photographs of selected fern and succulent species found on rock outcrops in the Stara Planina Mts. are presented in Figs. 3 and 4, respectively. The species with the highest frequency within the study area are Campanula wanneri Rochel, Heliosperma pusillum (Waldst. & Kit.) Rchb. subsp. pusillum, and Cystopteris fragilis (L.) Bernh. The most dominant life forms on the rock outcrops are hemicryptophytes (48.8%) and chamaephytes (31.2%) (Fig. 5A), which possess functional traits that enable them to endure the harsh conditions of these habitats (Tomaselli et al., 2018). These plants have strong root systems that anchor them to the rock, allowing them to penetrate cracks in search of water and minerals (Bacchetta et al., 2007). Hemicryptophytes’ traits offer protection against harsh climatic conditions at higher altitudes, while enhancing survival at lower and mid-elevations, where the growing season is longer (Carlsson et al., 1999; Körner, 2003). Furthermore, hemicryptophytes are dominant in the flora of Serbia (Diklić, 1984). In extreme cliff environments, the lignified underground and partially above-ground parts of chamaephytes help them withstand wind impacts and recover from harsh environmental conditions (Georghiou & Delipetrou, 2010). Chamaephytes, more tolerant BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fam. Caprifoliaceae Valeriana tripteris L. H EAM 1 S Fam. Violaceae Viola arvensis Murray T EA 2 S Fig. 2. A - Species and subspecies richness at the family level (families represented by one or two species are excluded); B - Species and subspecies richness at the generic level (genera represented by a single species are excluded) 83 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fig. 3. Representative fern species inhabiting rock outcrops on the Stara Planina Mts. (Serbia) (A - Asplenium ceterach, B - A. ruta-muraria, C - Cystopteris fragilis, D - Woodsia alpina, E - Asplenium trichomanes, and F - A. septentrionale. Photos by Jovana Stojanović 84 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fig. 4. Representative succulent species inhabiting rock outcrops on the Stara Planina Mts. (Serbia) (A - Sedum dasyphyllum, B - S. hispanicum, C - Jovibarba heuffelii, D - Sedum alpestre, and E - S. album). Photos by Jovana Stojanović 85 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia of mountainous conditions than other life forms (Lazarina et al., 2019), can complete their life cycle despite a short growing season, particularly at high altitudes (Vogiatzakis et al., 2003). Although the number of microhabitats suitable for colonization is limited (Davis, 1951), therophytes are relatively well-represented (9.6%), which may indicate an increase in disturbances and habitat degradation (Ranđelović et al., 2007). Disturbances such as rockfalls and erosion expose bare soil, creating open habitats that therophytes can quickly exploit. Their short life cycle allows for rapid reproduction, enabling them to establish before slower-growing species take root, thereby reducing competition. Geophytes, though limited by the space available for underground storage organs (Davis, 1951), are still present (7.2%), particularly in larger crevices or on ledges with greater soil accumulation. The diversity of life forms on rock outcrops can be attributed to the wide variety of microhabitats found in close proximity (Oettli, 1905). Fig. 5. A - Biological spectrum of the flora in the rocky habitats of the Stara Planina Mts. in Serbia (P - phanerophytes; Ch - chamaephytes; H - hemicryptophytes; G - geophytes; T - therophytes; and S - scandentophytes); B - Chorological spectrum of the flora in the rocky habitats of the Stara Planina Mts. in Serbia (AA - Arctic-Alpine; BOR - Boreal; CE - Central European; COSM - Cosmopolitan; EA - Eurasian; EAM - Eurasian Mountain; HOL - Holarctic; MED-SMED - Mediterranean-sub-Mediterranean; and PONT - Pontic) The phytogeographical analysis classified all recorded taxa into nine area types (Fig. 5B). The Eurasian Mountain area type is predominant (32%), including taxa characteristic of chasmophytic communities on the Stara Planina Mts. in Serbia, such as Campanula wanneri, Heliosperma pusillum subsp. pusillum, Silene flavescens Waldst. & Kit., S. lerchenfeldiana Baumg., Jovibarba heuffelii (Schott) Á. Löve & D. Löve, and Saxifraga pedemontana subsp. cymosa Engl. Some species from the Eurasian Mountain area type are represented in Fig. 6. The Eurasian area type ranks second (16%), including species like Asplenium ceterach, which are commonly found in rocky habitats. The predominance of taxa from these two area types suggests that the sampling localities exhibit montane-continental and temperate-continental characteristics, in line with the region's climate (Lakušić & Ćetković, 2007). The third most represented area type is Mediterranean- sub-Mediterranean (15.2%), which includes species found exclusively on carbonate rocks within the study area, such as Aurinia saxatilis subsp. orientalis (Ard.) T.R.Dudley, Sedum ochroleucum Chaix, and Satureja kitaibelii Wierzb. ex Heuff. Taxa belonging to this area type are typically associated with calcareous rocks and their presence in the study area can be attributed to the influence of the changed Mediterranean climate from the Aegean region, transmitted through river valleys and deep gorges, particularly the Vardar Valley and the Južna Morava River. This climate influence extends into the continental limestone areas of southeastern Serbia (Stevanović & Stevanović, 1995). Thermophilous and xerophilous habitats within the study area, especially low-elevation or south-facing carbonate rock formations, provide suitable conditions for species of the Mediterranean-sub-Mediterranean area type (Jušković et al., 2010). Additionally, the Holarctic area type is well represented (11.2%), including chasmophytic ferns such as Asplenium ruta-muraria and A. septentrionale (L.) Hoffm. 86 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia Fig. 6. Characteristic taxa of chasmophytic communities on the Stara Planina Mts. (Serbia) belonging to the Eurasian Mountain area type (A - Campanula wanneri, B - Heliosperma pusillum subsp. pusillum, C - Saxifraga pedemontana subsp. cymosa, D - Silene flavescens, and E - S. lerchenfeldiana). Photos by Jovana Stojanović This diverse composition underscores the Balkan Peninsula, particularly its central part, as a key convergence zone blending floristic elements from Central Europe, the boreal and Arctic Eurasian regions, as well as the eastern and central Mediterranean (Stevanović et al., 1995). The plant cover of rocky habitats is shaped by the bedrock composition, which influences the calcium carbonate levels in the soil. Species that thrive on limestone are typically calcicolous, while those preferring siliceous substrates are generally calcifugous (Kojić, 1984). The preference of 87 BIOLOGICA NYSSANA ● 16 (1) June 2025: 75-91 Stojanović et al. ● Floristic diversity of the rocky habitats of the Stara Planina Mountains in Serbia the recorded taxa for different bedrock types is presented in Tab. 1. The majority of taxa were found exclusively on siliceous rocks (90 species, 72% of all recorded taxa), followed by those documented only on limestone (20 species, 16%). A smaller proportion of taxa (15 species, 12%) were recorded on both bedrock types. Among the prominent chasmophytes exclusive to siliceous rocks are Campanula wanneri, Silene lerchenfeldiana, Asplenium septentrionale, and Woodsia alpina (Bolton) Gray, while those confined to limestone include Aurinia saxatilis subsp. orientalis and Silene flavescens. Some species, such as Asplenium trichomanes L., Cystopteris fragilis, Saxifraga paniculata Mill., and Asplenium ruta- muraria, were observed on both bedrock types. This is not surprising for Asplenium trichomanes and Cystopteris fragilis, as various subspecies of A. trichomanes are adapted to different substrates (e.g. A. trichomanes L. subsp. trichomanes prefers siliceous rocks, while A. trichomanes subsp. quadrivalens D.E.Mey. is more suited to calcareous rocks). Similarly, Cystopteris fragilis demonstrates a broad ecological tolerance for different substrate pH levels (Sádlo & Chytrý, 2009). On the other hand, Saxifraga paniculata and Asplenium ruta- muraria are generally considered calcicolous species (Axmanová, 2022). In the study area, Asplenium ruta-muraria is primarily found on calcareous rocks, while S. paniculata was more prevalent on siliceous rocks. This pattern can be explained by the presence of calcium compounds in acidic rocks, which may contribute to the formation of alkaline soil (Oettli, 1905; Lundquist, 1968). For example, silicate rocks like gneiss can contain calcium that accumulates in cracks, creating conditions conducive to the growth of calcicolous species (Lüth, 1993). As a result, microhabitats on different rock types can exhibit similar soil pH values (Larson et al., 2000), which in turn allows the development of the same plant species. Rocky habitats are often regarded as microclimatic refugia (Speziale & Ezcurra, 2015; Bátori et al., 2017; Fitzsimons & Michael, 2017), offering long- term shelter from harsh climatic conditions and enabling the survival of numerous relict species. These microhabitats act as buffers against extreme environmental conditions, making rock crevices vital refuges for arctic-alpine species, especially those found south of the Arctic belt (García et al., 2020). The presence of arctic-alpine species in rock vegetation is a legacy of climatic fluctuations during glaciation and deglaciation, which confined their earlier distribution to mountainous regions and cliffs (Larson et al., 2000). Relict species thrive in low- competition microhabitats, such as crevices, where limited space restricts the growth of competing plants (Crawford, 1989). In the study area, 9% of the recorded species are considered glacial relicts, including Aster alpinus L., Arabis alpina subsp. caucasica (Willd.) Briq., Cerastium alpinum L., Sedum annuum L., Juncus trifidus L., Luzula spicata (L.) DC., Poa alpina L., P. laxa, Primula minima L., Saxifraga paniculata, and Woodsia alpina. Chasmophytic plant communities are of significant biogeographical importance due to the high number of endemic taxa they support. These endemic species flourish in steep, rocky environments with challenging soil conditions, where limited vegetation cover minimizes biotic interactions (Panitsa & Kontopanou, 2017). In this study, two Balkan endemic taxa were identified: Centaurea stoebe subsp. serbica (Prodan) Ochsmann and Dianthus moesiacus Vis. & Pančić (Tomović et al., 2014). Several species recorded on the rock outcrops within the study area are designated as strictly protected or protected under national legislation (Official Gazette of the Republic of Serbia, No. 5/2010, 47/2011, 32/2016, and 98/2016). Strictly protected species include Campanula wanneri, Dianthus moesiacus, and Veronica barrelieri Roem. & Schult. Protected species encompass Silene lerchenfeldiana, Juniperus communis subsp. nana Syme, Vaccinium myrtillus L., Geranium macrorrhizum L., Hypericum maculatum Crantz, Satureja kitaibelii, Primula minima, Drymocallis rupestris (L.) Soják, Galium odoratum (L.) Scop., and Saxifraga pedemontana subsp. cymosa. Conclusion This study highlights the remarkable floristic diversity and ecological significance of rock outcrops in the Stara Planina Mts. in Serbia. It identifies a wide range of vascular plant species, including several new regional records. The adaptation of chasmophytes to harsh environmental conditions emphasizes their essential role in these unique ecosystems, which host a variety of endemic and relict species. The findings highlight the urgent need for conservation efforts, particularly for species protected by national legislation, in light of threats from habitat degradation and climate change. Furthermore, the study calls for further research to fully assess the biodiversity of these habitats and to develop effective conservation strategies to preserve these valuable ecological resources. Acknowledgements. 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