Using nuclear DNA C-values for 539 angiosperms in China, we examined the variation of these values among growth forms and taxonomic groups and the relationship of these values with invasiveness. Mean DNA C-value of the 539 angiosperm species was 4.06 pg. Mean DNA C-value was (1) significantly lower for woody species (1.84 pg) than for herbaceous species (5.02 pg); (2) significantly lower for 360 dicots (2.20 pg) than for 179 monocots (7.80 pg); (3) significantly lower for annuals (2.78 pg) than for perennials (6.65 pg); (4) significantly lower for 134 weed species (193 pg) than for herbaceous non-weeds (6.75 pg) and for several families that have an unusually high proportion of weed species; (5) significantly lower for 47 exotic weed species (1.76 pg) than for 134 native weeds (1.93 pg), but significantly lower than that of “non-weedy” herbaceous species (6.75 pg); (6) lower for weeds than for “non-weedy” species in same genus or family; and (7) in herbaceous species, generally lower for weedy compared to “non-weedy” species, with some exceptions such as Avena fatua, whose DNA C-value is as high as 14.15 pg, contrarily, and some “non-weedy” herbaceous species in Cruciferae and Cucurbitaceae with very low values. DNA C-values varied much greatly among families. The relationship between DNA C-value and ploidy is not clear, whereas the mean DNA per basic genome decreased with increases in inploidy. Conclusion: DNA C-value is of practical value in the forecast of the invasiveness of exotic species. However, such predictions must be made with comparisons within families (or genus) because the DNA C-values vary greatly between woody and herbaceous species, between monocots and dicots, between annuals and perennials, and especially among families.