This paper discusses acquisitions to the adventitious flora of the Netherlands, mainly found in the year 1964. 1. Erucastrum nasturtiifolium (Poir.) O. E. Schulz was most likely introduced with blocks of granite for the “Delta-works”, near Hellevoetsluis, prov. of South Holland. It is indigenous in parts of Southern and Central Europe. Differences between this species and the native E. gallicum (Willd.) O. E. Schulz are given. 2. Euphorbia dentata Michx., a native of the Central United States and Mexico, was found along a highway near Bodegraven, prov. of South Holland. As far as known to us this is the first record of introduction of the species into Europe. 3. Trientalis borealis Raf., a North American species, was found in a wood near Apeldoorn, prov. of Gelderland, where it was probably unintentionally introduced with American ferns. It has grown there at least since 1931 and has established itself. 4. Solanum nigrum L. f. luridum Wessely, a form of subspecies schultesii (Opiz) Wessely with yellow-green berries, was found as an alien near ’s-Gravenhage, prov. of South Holland. 5. Bidens bipinnatus L. was earlier mentioned as an adventitious species for the Netherlands, but the specimens on which the records were based appeared to belong to B. subalternans DC. The true B. bipinnatus was found in 1964, together with no. 2 of this series and several other aliens. Differences between the two Bidens-species are given. B. bipinnatus originally occurs in the eastern United States and E. Asia. 6. Erigeron annuus (L.) Pers. All the Netherlands specimens hitherto mentioned under this name appeared to belong to E. strigosus Mühlenb. ex Willd. (See Gorteria 2, no. 1, p. 9—12). In 1964 numerous specimens of the true E. annuus were found at Wageningen, prov. of Gelderland. 7. A number of plants escaped from cultivation.