A variação na composição química do óleo essencial das folhas em três populações silvestres de Lychnophora ericoides, com ou sem odor, indicou a presença de dois grupos de óleos em relação ao odor das amostras. O primeiro incluiu amostras de odor aromático contendo altas percentagens de -bisabolol (34 23%) e o-cimeno (8,4 6,9%). No grupo II, as amostras não apresentaram qualquer odor e os constituintes majoritários foram o óxido de cariofileno (11 9%) e o -elemeno (5,7 6,9%). Em todas as populações estudadas co-existem os dois tipos de óleos, embora a maioria das amostras aromáticas provenientes do Parque Estadual da Serra de Caldas Novas se diferenciem quimicamente daquelas do Parque Nacional de Brasília e de Santo Antônio do Descoberto. As variações químicas sugerem claramente, além da influência geográfica, diferenças genéticas entre indivíduos nas populações. O alto conteúdo de -bisabolol suporta o uso medicinal folclórico de arnica como antiinflamatório.Variations in the composition of the leaf essential oils of wild Lychnophora ericoides, with and without scent, which were grown in three sampling sites, were examined by GC-MS. Results were submitted to principal component and cluster analysis which allowed for two groups of essential oils to be distinguished with regard to scent: cluster I with specimens exhibiting an aromatic scent and containing a high percentage of -bisabolol (34 23%) and o-cymene (8.4 6.9%); cluster II with specimens without any scent and characterised by a high percentage of caryophyllene oxide (11 9%) and -elemene (5.7 6.9%). The two types of oil coexist in all the populations under study, although patterns of aromatic samples deriving from Caldas Novas' State Park reveal chemical differences in relation to the samples from Brasília's National Park and Santo Antônio do Descoberto. Such chemical variations clearly suggest, apart from a geographical influence, genetic differences between individuals in the populations. The high content of -bisabolol supports the folk medicinal use of arnica as anti-inflammatory.Keywords: Lychnophora ericoides, Asteraceae, essential oils, chemical variability IntroductionThe genus Lychnophora Mart. (Asteraceae) consists of approximately 34 species, all of which grow in restricted regions of central Brazilian Cerrado at altitudes ranging from 950 to 1800 m above sea level in sandy sites, usually inside woodland and scrubs.1-3 L. ericoides Mart. is the most popular species, whose leaves are frequently aromatic and commercialised in local markets as analgesic and anti-inflammatory agents. 4,5 Its characteristic constituents are sesquiterpene lactones showing antiproliferative activity, 6-8 as well as flavonoids with anti-inflammatory effects, 9 triterpenes, 7,10 lignans, and caffeoylquinic acids with analgesic activity. 4,11 In the first phytochemical study of the essential oil of L. ericoides we identify a high degree of variability in the quantity and composition of leaf essential oils from wild populations with and without scent, each one growing on dif...