Chemical Systematization of the Genus Foeniculum Mill. Based on the Accumulation and Qualitative Differentiation of the Essential Oil

Abstract

All members of the genus Foeniculum Mill. accumulate volatiles, including terpenoid and phenylpropanoid compounds. The genus shows a large diversity from both the morphological and chemical points of view. Based on the former morpho-phenological systematization, two subspecies (subsp. piperitum and subsp. capillaceum) and three varieties (var. vulgare, var. dulce, and var. azoricum) were distinguished. As a result of detailed analysis of 185 gene-bank accessions and evaluation of literature references a more sophisticated chemical classification of the genus has been completed by us. According to our anatomical investigations the oil ducts (vittae) appear in the early stages of development of generative organs, even at the time of bud formation. The maximum yield of essential oil and dry matter coincide with the ripening phase of the fruit, while the relative percentage of oil shows its maximum much earlier, at the beginning of fruit development, when the accumulation process of starches is just about to start. However, for the chemical classification of the genus, analysis of the oil distilled from the ripe fruits seems to be optimal because of its relative quantitative and qualitative stability. Based on the evaluation of Foeniculum vulgare (Mill.) populations of different origin the distinction of F. vulgare subsp. piperitum seems to be a relatively simple procedure because of the unique morphological markers and the presence of piperitone and piperitone oxide, as well as the high accumulation level of limonene. Similarly, in the case of F. vulgare subsp. capillaceum var. azoricum, the relatively high level of (E)-anethole and low accumulation level of methyl chavicol helps the orientation. Three inner groups of chemovarietal rank of F. vulgare subsp. capillaceum var. dulce can be distinguished according to the accumulation level of (E)-anethole and methyl chavicol. The intra-specific chemical classification of F. vulgare subsp. capillaceum var. vulgare group raises many more difficulties. Evaluating a large number of populations, as well as the literature references, distinction of three chemovarieties [(E)-anethole, fenchone and methylchavicol types] and four chemoforms of a lower chemical rank (segregated by a different ratio of (E)-anethole and methyl chavicol) were identified.