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The Mediterranean flora is characterized by the abundance of aromatic plants. The feature differentiating these plants from all others, in spite of the fact that they belong to many different families, is the production of chemically related secondary compounds, the low molecular weight and volatile isoprenoids. This remarkable presence of aromatic species is important in determining the phytotoxic potential within this ecosystem. Such plants make a significant contribution to phryganic Mediterranean ecosystems both in terms of species number and biomass. Thus, the essential oils play an important role in this ecological context. Mediating various processes in the frame of an ecosystem, they become indirectly beneficial to the plants, considering their involvement in processes of adaptative character in Mediterranean ecosystem. For this reason, our research group carried out a series of studies on the possible phytotoxic properties of aromatic plants that, being rich in active principles, are considered a primary source of potential allelochemicals.The focus of this overview is direct to have an overall idea about the chemistry and antigerminative activity of essential oils of some Mediterranean aromatic plants and their main constituents.

A new menthol cultivar of Menthax piperitaL. bred in East Slovakia was evaluated for the biological activity of its essential oils (EOs). The content and composition of the EO components changed during plant development and the different effects of samples collected each month (April - September) within the growing season were noted. EOs are considered to be an important source of potential allelochemicals. Changes in EO composition influenced phytotoxic activity. Stimulation and inhibition of seed germination and root elongation occurred with different EO concentrations. The four tested bacterial strains presented different resistance to the samples collected in different growing periods.

The chemical composition of the essential oils of two endemic plants of Turkey, Stachys rupestrisMontbret et Aucher ex Benth. and Salvia heldreichianaBoiss. ex Benth., were obtained by hydrodistillation and studied by GC and GC–MS. In all, 46 compounds were identified, 22 for S. rupestrisaccounting for 94.6 % of the total oil and 30 for S. heldreichiana, accounting for 91.9 % of the total oil. The presence of diterpenoids (50.7%) characterized the oil from S. rupestris, while S. heldreichianaoil was rich in oxygenated sesquiterpenes (78.9%). The essential oils were evaluated for their in vitropotential cytotoxic activity on three human cancer cell lines. The oil of S. rupestrisshowed the higher antiproliferative activity against PC-3 and MCF-7 cancer cell lines.

Aromatic plants can interfere in the Mediterranean ecosystem, mainly by the introduction in the environment of volatile compounds. For this reason, we studied the chemical composition and the possible phytotoxic and antimicrobial activities of the essential oil extracted from leaves of Tunisian Artemisia herba-alba Asso. The chemical composition of the essential oil, obtained by hydrodistillation, was analyzed by GC and GC-MS. In all, 24 compounds were identified. The main components were camphor (39.1.%), chrysanthenone (15.0%) and cis-thujone (7.8%). The essential oil was evaluated for its in vitro phytotoxic activity against germination and initial radical growth of Raphanus sativus L., Lepidium sativum L., Sinapis arvensis L., Triticum durum L. and Phalaris canariensis L. seeds. The radicle elongation of the five seeds was affected to different extents by the oil, while germination was not affected. The oil, when tested against eight selected bacterial strains, showed low antimicrobial activity. The chemical composition of the oil of A. herba-alba can help in the chemosystematics of this complex genus. However, the recorded biological activities seem to be neither ecologically nor medicinally significant.

The chemical composition of the essential oil from aerial parts of Calamintha nepeta(L.) Savi, collected in the Campania Region, was obtained by hydrodistillation and analyzed by GC and GC-MS. In all, 42 compounds were identified. The oil was characterized by a prevalence of the sesquiterpenic fraction (80.8%). The main components were 1,10-di-epi-cubenol (18.5%), allo-aromadendrene epoxide (11.4%) and cadalene (5.7%). The essential oil was evaluated for its in vitropotential phytotoxic activity against germination and initial radical growth of Raphanus sativusL., Lepidium sativumL., Sinapis arvensisL., Triticum durumL. and Phalaris canariensisL. seeds. The essential oil showed no antioxidant activity.

The present paper reports the chemical composition, antioxidant and antibacterial activities of several essential oils and their components. Analysis showed that three oils (Carum carvi L., Verbena officinalis L. and Majorana hortensis L.) contained predominantly oxygenated monoterpenes, while others studied (Pimpinella anisum L., Foeniculum vulgare Mill.) mainly contained anethole. C. carvi, V. officinalis and M. hortensis oils exhibited the most potent antioxidant activity, due their contents of carvacrol, anethole and estragol. Antibacterial action was assessed against a range of pathogenic and useful bacteria and fungi of agro-food interest. V. officinalis and C. carvi oils proved the most effective, in particular against Bacillus cereus and Pseudomonas aeruginosa. Carvacrol proved most active against Escherichia coli, and completely inhibited the growth of Penicillium citrinum. The oils proved inactive towards some Lactobacilli strains, whereas single components showed an appreciable activity. These results may be important for use of the essential oils as natural preservatives for food products.