Abstract: Many reports have found a statistically negative correlation between DNA C-value and plant invasiveness, with meristematic karyon size playing a key role in this correlation according to previous research. We hypothesized that meristematic karyon size could be applied as an evaluation index of plant invasiveness for at least some taxa. To test this hypothesis, we examined the sizes of karyons, cells, and mitosis rates of five Vicia species with different invasiveness and DNA C-values, and also investigated their seed production, seedling weight/dry seed weight (similar to relative seedling growth rate), and their life spans. Results showed that plants with smaller meristematic karyons were prone to have smaller chromosomes, karyons, cells, and seeds, quicker mitosis, higher relative seedling growth rate, shorter generation time, and produce more and smaller seeds. Furthermore, among the five Vicia species, plants with smaller meristematic karyons exhibited higher invasiveness, which may be explained by two aspects: (1) smaller seeds with much higher seed production; and (2) higher rates of cell division and seedling growth with shorter generation times. The effects of meristematic karyon size on plant invasiveness coincided with that of the DNA C-value. Therefore, for plant invasiveness evaluation models, meristematic karyon size has potential value in invasiveness assessment due to its convenience and lower expense, though more work is needed to determine its application scope and methodology.