Investigation of the aerial parts of Xanthocephalum gymnospermoides var eradiatum led to the isolation of two new labdane-type of diterpenes, namely, 8 alpha,13S-epoxylabdane-14S,15-diol (1) and methyl grindelate (2). In addition, grindelic acid (3), 7 alpha, 8 alpha-epoxygrindelic acid (4), 7 alpha-hydroxy-8(17)dehydrogrindelic acid (5), 17-hydroxygrindelic acid (6) and 4,5-epoxy-beta-caryophyllene (7) were obtained. The isolated compounds were characterized by spectral means. The absolute configuration of compound 1 was established by chemical correlation with 8 alpha,13S-epoxy-15-nor-labdan-14-oic acid methyl ester of known absolute stereochemistry and by using the advanced Mosher's ester methodology. The results of the present investigation indicated that the known compound barbatol (8) could be an enantiomer of compound 1. Compounds 1-3 and 7 caused significant inhibition of the radicle growth of seedlings of Amaranthus hypochondriacus.