Biosystematic and chemosystematic studies in five South American species of Conyza (Asteraceae)

the composition of the essentials oils of five species of conyza less from argentina was determined by gas chromatography-mass spectrometer. this composition is associated to morphological and cytogenetic characters. the monoterpenes constitute more than 60% of the essential oils in c. blakei, c glandulitecta, c. sumatrensis var. sumatrensis and c. sumatrensis var. floribunda, in which limonene is the predominant compound. in c. bonariensis and c. primulaefolia the monoterpene content constitute less than the 40%. c. bonariensis presents only 13% limonene, while in c. primulaefolia it is absent. the similarity analysis of monoterpenes showed a relationship between the morphological and cytogenetic analysis, and the monoterpene content character seems to be important in biosystematic studies of the group studied. in general, c. sumatrensis var. sumatrensis is the species with more ancestral characters, while c. bonariensis and c. primulaefolia show more derived ones.