Karyology and phylogeny of some Mesoamerican species of Zamia (Zamiaceae)

Chromosome numbers and karyotypes of four species of Zamia L. (Zamiaceae) are described. Plants of Z. manicata from Colombia are 2n = 18 with eight metacentric (M), four submetacentric (S), two acrocentric (A), and four telocentric (T) chromosomes. Plants of Z. ipetiensis from Panama are 2n = 23 with 3M + 4S + 2A + 14T. Plants of Z. cunaria from Panama have two different chromosome numbers, 2n = 23 with 3M + 4S + 2A + 14T and 2n = 24 with 2M + 4S + 2A + 16T. Plants of Z. acuminata from Costa Rica and Panama are 2n = 24 with 2M + 4S + 2A + 16T. On the basis of the occurrence of a one‐to‐two‐ratio in the variation of M‐ and T‐chromosome numbers in the karyotypes, centric fission or fusion are considered for their potential involvement in the chromosome variation of these plants. Data deriving from morphology and karyology, interpreted in a cladistic framework, suggest that centric fission rather than centric fusion is involved in the karyotype diversification of the four species and their closest Mesoamerican allies.