## 1 Introduction  
Heartleaf oxeye (_Telekia speciosa_ ([PERSON]) [PERSON]) is a perennial, herbaceous, and melliferous plant that is native to mountainous areas in southeast Europe: Carpathians, the mountains of the Balkan Peninsula; northern Anatolia; and Caucasus. Climate change, however, favors colonization of new areas in Europe by the plant. In most European countries, as well as in North America and Japan, _T. speciosa_ is an introduced species. One of the largest colonies of this plant, with an area of about 2 ha, can be found in Poland on the bank of the Jasiolka River near Tylawa. Moreover, in Poland, the plant is found in the Bieszczady and Mazury regions. In Czech Republic, _T. speciosa_ has been classified as an invasive neophyte. It colonizes many areas almost throughout Poland, Czech Republic, Ukraine, Balkans, and other European countries, mainly at middle and high elevations. Heartleaf oxeye became naturalized and, in many cases, spread along streams, rivers, and forest tracks, and to forest clearings and abandoned montane meadows. The species was named after the 19 th-century Hungarian aristocrat [PERSON], who valued its beauty and financed the botanical research of German scientist [PERSON]. _T. speciosa_ typically grows in clusters. The plant may reach 150-200 cm in height and blooms with multi-flowered, yellow capitula [1; 2; 3]. _T. speciosa_ is an essential-oil-bearing plant well-known for its richness of biologically active constituents, both volatiles and non-volatiles [4]. Essential oils (EOs) are complex mixtures of volatile compounds that are biosynthesized inside intracellular compartments in diverse plant organs. These volatiles include many biologically active compounds, mainly terpenes, formed from isopentyl diphosphate (IPP) or 3,3-dimethylallyl diphosphate (DPP) units [2]. The roots of _T. speciosa_ contain EO characterized by the dominance of volatile sesquiterpene lactone: isoalantolactone. Aerial parts of the plant have been shown to contain isoalantolactone in their EOs as well, albeit in smaller quantities. This biologically active molecule has been a subject of numerous studies. For example, isoalantolactone, in combination with penicillin G, exhibited synergism against \(\beta\)-lactamase-positive _Staphylococcus aureus_ strains, even including methicillin-resistant _S. aureus_[5; 6]. Aerial parts of _T. speciosa_ contain sesquiterpene lactones of the eudesmane, guaiane, xanthane, and pseudoguaiane types [4; 7]. Flowers of the plant were identified as a source of many different terpenids, including those of high molecular mass, such as calenduladiol esters. The esters and a sesquiterpene lactone (asperilin) isolated from the flower extract were tested against human cancer cells. Flower extracts and sesquiterpene lactones isolated thereof showed high antiproliferative activity against the cancer cell lines tested [7; 8; 9]. Previous analysis of _Telekia speciosa_ flower EO, distilled from plants grown in Poland, revealed the presence of isoalantolactone (23.0%) and 10-isobutyryloxy-8,9-epoxythymol isobutyrate (20.5%) as dominant constituents [10]. These two compounds were present in much lower amounts in a recently studied _T. speciosa_ EO [11], probably due to the fact that the EO was obtained from aerial parts, in which flowers represented only a minor part. In total, EOs from aerial and unground parts of _T. speciosa_ from Bosnia and Herzegovina contained 67 compounds. The major volatiles identified in green parts were (_E_)-neroldold (11.5%) and carryophyllene oxide (10.5%), while isoalantolactone predominated in roots (83.4%) [11]. EO from the aerial parts of _T. speciosa_ collected in Serbia contained (_E_,_Z_)-farnesol (12.0%), (_E_)-neroldold (10.2%), and \(\beta\)-caryophyllene (5.4%) as major constituents [5]. Such variability in the composition of EOs obtained from the same species is not unusual [12]. Several studies linked the chemicals present in EOs to the biological properties of the oils. EOs from _T.