###### Abstract  
New and detailed data are presented on the phytochemical composition of the volatile and non-volatile organic compounds of the Mediterranean endemic species _Portenschlagiella ramossissima_ (Port.) Tutin. Both the essential oil and hydrosol were obtained from the air-dried plant by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The volatile compounds from the fresh and air-dried plants and from the hydrosol were isolated for the first time by headspace solid-phase microextraction using two fibres of different polarity. The benzene derivative group was the predominant group in all samples, with myristicin being the most abundant component of all. The non-volatile compounds of the methanol extract were analyzed by ultra-high-performance liquid chromatography-high-resolution mass spectrometry with electrospray ionisation, and three flavonoid glycosides, one anthocyanin diglycoside, and lipid derivatives were detected. Both the chemical composition and biological activities of this plant have been described in a very limited number of publications, making it an interesting source for further study. The antiphytoviral activity of the essential oil and hydrosol showed that both extracts significantly reduced the number of lesions on the leaves of local host plants infected with tobacco mosaic virus. Moderate antiproliferative activity of the methanol extract was detected in three cancer cell lines, cervical cancer cell line, human colon cancer cell line and human osteosarcoma cell line, using the MTS-based cell proliferation assay. Based on the results, we highlight this plant as a new source of bioactive compounds and natural phytotherapeutic agent that deserves further investigation. P ARTICLE, 20  
sabinene, \(\alpha\)-terpinene, and other essential oil constituents were among the more abundant components in the volatilome of _P. ramossissima_[4]. Since ancient times, essential oils have been used in traditional medicine around the world for their beneficial effects on human health. The described effects of essential oils, such as antiproliferative, antimicrobial, antioxidant, insecticidal and other effects [5; 6; 7], are constantly being supplemented by new findings and new effects such as antiphytoviral activity [8; 9]. In addition to their role in folk medicine, essential oils are components of pharmaceuticals and are used in the agricultural and food industries. Numerous preclinical studies have documented various biological activities in a variety of cellular and animal models, also elucidating their mechanisms of action and pharmacological targets. Nevertheless, the paucity of human studies limits the potential of essential oils as effective and safe phytotherapeutics [10]. In an ecological context, secondary metabolites establish a relationship between plants and their ecosystem; for example, volatile compounds can repel phytophagous organisms, including viruses and phytoplasma vectors [11]. Among the non-volatile organic compounds of plants, there are also many bioactive constituents with numerous beneficial effects for plants and also great health benefits for humans. Therefore, some of them, such as flavonoid glycosides, are used as drugs and dietary supplements due to their good bioactivity and low toxicity [12]. The antiproliferative effect of methanol extract has already been demonstrated for some Apiaceae and other aromatic plants, but as far as we know, no such data have been published for _P. ramossissima_. Most of the studies performed so far on the antiproliferative and cytotoxic activity of species of the Apiaceae family have dealt mainly with essential oils [13; 14; 15; 16; 17; 18]. Somewhat fewer studies have been conducted with various extracts of Apiaceae plants, including methanol, ethanol, dichloromethane, chloroform, and others [19; 20; 21; 22; 23]. Considering the insufficient data describing the phytochemical composition of _P. ramossissima_, the first objective of our research is a detailed analysis of the volatilome of this plant species.