From a comparison of the chromosome numbers of different species, it appears that 11 is the basic number of Peperomia and 12 of Piper. Variation in the reports of chromosome number of the same species may be due to occurrence of chromosomal biotypes.
The trend of evolution in the two genera (Peperomia and Piper) appear different, numerical and structural change in the former, and polyploidy in the latter. The basic number (x=11) is represented by Peperomia argyreia, where structural alteration is clear. x×12 is represented by Pep. metallica, Pep. obtusifolia and Pep. pellucida, polyploidy occurring only in the last one.
Piper cubeba (2n=24), P. magnificum (2n=24) and P. longum (2n=48), probably form a basic group of Piper. P. nigrum (2n=36, 60) is more advanced in chromosome structure. P. betle (2n=64) represents a different line having x=8 or 16.
Records of chromosome number suggest that Peperomia is more primitive than Piper.