The pantropical weed Bidens pilosa (Asteraceae) is a species with several taxonomic problems. Recently it has been shown to be a complex of different species. To shed light on this problem in Brazil, dichloromethane extract of leaves of several populations corresponding to three proposed species for the complex in southeastern Brazil (B. pilosa, Bidens alba and Bidens subalternans) were analyzed by GC-MS. Twenty-four substances were detected, of which four resemble polyacetylenes, the others sesquiterpenes. Five sesquiterpenes tentatively identified as E-caryophyllene, alpha-humulene, germacrene-D, bicyclogermacrene and alpha-muurolene were found in all three Bidens species. The polyacetylene phenylhepta-1,3,5-triyne was identified,only in B. alba. Multivariate analysis (cluster and principal component analyses) separated the three entities, suggesting that these compounds could represent a useful tool to distinguish species in the B. pilosa complex. (c) 2004 Elsevier Ltd. All rights reserved.335479486