Nuclear DNA contents for 104 Macaronesian angiosperms, with particular attention on Canary Islands endemics, were analysed using propidium iodide flow cytometry. Prime estimates for more than one-sixth of the whole Canarian endemic flora (including representatives of 11 endemic genera) were obtained. The resulting 1C DNA values ranged from 0.19 to 7.21 pg for Descurainia bourgeauana and Argyranthemum frutescens, respectively (about 38-fold difference). The majority of species, however, possessed (very) small genomes, with C-values <1.6 pg. The tendency towards small nuclear DNA contents and genome sizes was confirmed by comparing average values for Macaronesian and non-Macaronesian representatives of individual families, genera and major phylogenetic lineages. Our data support the hypothesis that the insular selection pressures in Macaronesia favour small C-values and genome sizes. Both positive and negative correlations between infrageneric nuclear DNA amount variation and environmental conditions on Tenerife were also found in several genera.