First report of Tripleurospermum rosellum ( Asteraceae ) from Bulgaria and its distinction from the allied T. oreades and T. caucasicum

Kunev, G. & Petrova, G.: First report of Tripleurospermum rosellum ( Asteraceae ) from Bulgaria and its distinction from the allied T. oreades and T. caucasicum . — Fl. Medit. 33: 39-48. 2023. — ISSN: 1120-4052 printed, 2240-4538 online. Tripleurospermum rosellum is here reported as native to Bulgarian flora for the first time based on materials gathered in the East Rhodope Mts. The revision of herbarium materials revealed that the taxon has been collected from several different localities in the same region of the country over the past 80 years. A detailed presentation on its morphology, distribution and habitat characteristics in Bulgaria are presented. The Greek collections of Tripleurospermum oreades are to be referred to T. rosellum . The species is also confirmed for the mainland of European Turkey.


Introduction
Tripleurospermum Sch.Bip.(Asteraceae) is a monophyletic lineage within Anthemideae tribe (Inceer & al. 2018).It is a critical genus of about 40 species, distributed almost exclusively in the Northern hemisphere with exception of Tripleurospermum inodorum (L.) Sch.Bip, being distributed globally (POWO 2021).With nearly 30 species, half of which were reported endemic, Turkey has been considered its main center of diversity (Inceer & Ozcan 2021).
During a phytosociological study performed by the first author in the period 2018-2020, in the East Rhodope Mts., Bulgaria, a representative of the genus Tripleurospermum was registered.It drew attention due to its perennial habit, low, ascending, unbranched stems, each bearing a single capitulum, and unusually early flowering -late April.The species has been collected from several different localities in different developmental stages during this period.Our study showed that the collected specimens do not correspond to any of the taxa within Tripleurospermum reported from Bulgaria.Further comparison with herbarium collections and a crosscheck with relevant literature sources proved that its correct taxonomic identity is Tripleurospermum rosellum var.album E. Hossain.
The similar T. oreades (Boiss.)Rech.f. has been reported from a single site in Northeast Greece, which represents the sole European record of that taxon (Strid & Lassen 2000).Its close proximity (40 km in SW) to the sites of T. rosellum in Bulgaria impelled us to compare collections from both sides of the Greek-Bulgarian border.Examination of representative material conclude that all of it belongs to T. rosellum.
The aim of the current paper is to report T. rosellum as a member of the Bulgarian flora and to confirm its occurrence in Northeast Greece and continental European Turkey.Our conclusions are supported by a detailed description of its morphology (incl.photographs and SEM micrographs), distributional notes and habitat indications.

Materials and Methods
The specimens collected by us were deposited at SO and SOM (herbarium acronyms follow Thiers 2022).Identification is based on the treatments of Boissier (1875) and Hossain (1975), further corroborated with the aid of additional relevant literature (Hayek 1931; Kay 1976; Pobedimova 2000; Inceer & al. 2012; Inceer & Ozcan 2021), and comparison with specimen images, including types, kept at BR, K, E, WU, P, JE, and G (G-BOIS), and with photographs of live plants (Dimopoulos & al. 2021; Danin & Fragman-Sapir 2021).Herbarium collections of Tripleurospermum, Matricaria and Chamaemelum kept in Bulgarian herbaria (SO, SOM and SOA) were revised.The list of examined specimens is presented in Annex 1. Cauline leaf and a capitulum with not fully matured fruits of T. oreades collected in Greece were studied and compared with Bulgarian samples.Our key and morphological descriptive data of the discussed taxa is based on the cited specimens.Cypsela morphology was studied by SEM, selected micrographs being shown in Fig. 1, additional micrographs with higher resolution being enclosed in Annex 2. The distribution of the taxon in Bulgaria is mapped at a scale 1:300 000.Habitat characteristics and species lists at the studied sites are based on our personal observations.Climatic characteristics of the investigated region are presented according to numerical weather prediction model (Climate-Data 2021).

Distinction of morphologically similar taxa
Tripleurospermum rosellum is morphologically similar to T. oreades and T. caucasicum (Enayet Hossain 1975), both of which have recently been considered as conspecific (POWO 2021; Greuter 2021), and with controversial taxonomic value.We here accept their specific distinctness, using several characters for their discrimination (Table 1).
The Greek and Bulgarian material studied possess glands at the tip of disk corolla lobes; the corona of cypselae is usually lobed, with obtuse, obovate lobes; the median cypsela rib is distinctly broader than the lateral ones; all these features are typically present in T. rosellum.Therefore, we conclude that the Bulgarian and Greek collections initially reported as T. oreades (Strid & Lassen 2000) are better treated as T. rosellum var.album.
To our knowledge, the only references for the occurrence of this taxon in European Turkey are from Gökçeada island (Seçmen & Leblebici 1978; Inceer & Hayırlıoğlu-Ayaz (2014).Here, we confirm the presence of the species on the mainland of European Turkey based on material collected in the Istanbul area (B.Davidoff , SOM 79928, sub Chamaemelum inodorum (L.) Vis, Annex 1).
In Bulgaria, T. rosellum has been misidentified as T. inodorum, T. tenuifolium or T. caucasucum (Annex 1), so here we present an updated key to ease the identification of the representatives of the genus in Bulgaria.

Distribution and habitat in Bulgaria
Tripleurospermum rosellum has not been reported previously from the territory of Bulgaria (Kuzmanov 2012; Stoyanov & al. 2021).The revision of herbarium materials of the genera Tripleurospermum, Matricaria, and Chamaemelum kept in Bulgarian herbaria (SO, SOM and SOA) has shown that the taxon has been collected repeatedly in the past 80 years, but was apparently misidentified (Annex 1).
In the country, the species so far has been recorded only in the East Rhodope Mts. (Fig. 2), a region with established phytogeographical connections with the eastern Mediterranean and Aegean areas through the valleys of the Arda and Maritza rivers.
The region is influenced by transitional Continental-Mediterranean climate (Velev 2002).Mean annual temperatures for the different localities ranges from 12.0°C to 13.3°C, while the average temperature for January exceeds 0°C in all know sites of the taxon.Annual precipitation ranges from 640 to 900 mm, with maximum precipitation in December.
In all Bulgarian sites, the species displays ruderal behavior.It was found on eroded slopes and bare ground, on roadsides, field margins, in overgrazed pastures, in grassland or scrub communities of low density, and open thermophilous woodlands mostly of deciduous oaks or pine groves, in xeric to xero-mesic conditions, at up to 400 m of elevation.It was most often observed in sunny locations or in the sunniest spots of scrub or woodland.
The substrates were mostly siliceous, on ground trampled by sheep herds or compacted by vehicle traffic.
In Bulgaria, T. rosellum could be observed only for a short period between end of April and mid-May.For this reason and because of its superficial resemblance with other Anthemideae (e.g.Anthemis cretica L., Anthemis rumelica (Velen.)Stoj.& Acht.), the species was probably overlooked until now.

Conclusion
Tripleurospermum rosellum is here added to the Bulgarian flora as a native species.Particularly, in Greece, it is replacing T. oreades with which it had been confused.In Bulgaria it is represented only by its white-ligulate variety.In the country, it is documented up to now only from the East Rhodope Mts.Since the taxon was registered in about ten relatively distant localities with several tens to several hundred individuals and it is more or less ruderal with the ability to produce abundant number of seeds, we consider that at present it does not require any conservation measures.Based on the revision of herbarium collections, the taxon is confirmed also for the territory of Northeast Greece and continental European Turkey.We assume that it is more widespread on the territory of Bulgaria, but was probably overlooked, due to its short flowering period, misinterpretation, and gaps in floristic sampling.

Fig. 1 .
Fig. 1.Habitus (A), capitulum cross-section (B), involucral bracts (C), cypselae in different development stages and disk flowers (D) with black arrow pointing the glandules on the tips of corolla lobs (all extracted from exsiccates), fruit SEM micrographs with black arrows pointing the characteristic mucilaginous cells on adaxial (E) and abaxial (F) surface of Tripleurospermum rosellum from East Rhodope Mts., Bulgaria.Photos for the Fig. 1A, B, C and D made by Georgi Kunev.

Fig
Fig. 1s.SEM morphographs (A, B and C) and photographs (D) of cypselae of Tripleurospermum rosellum from East Rhodope Mts., Bulgaria.Features as lobate corona with obtuse-obovate lobs, truncate base, broad median rib, reticulate surface, and mucilaginous cells are all well represented on the morphographs.Mucilage envelope stained with iodine in pale orange (D), photographed under stereomicroscope (×4).