Phenotypic variation seems not to be associated with the genetic profile in Zygopetalum (Orchidaceae): a case study of a high-elevation rocky complex

Hybridization associated with polyploidy studies is rare in the tropics. The genus Zygopetalum (Orchidaceae) was here investigated as a case study of Neotropical plants. In the Ibitipoca State Park (ISP), Southeast, Brazil, occurring in outcrops of campos rupestres, it was observed a wide phenotypic variation involving Z. maculatum and Z. triste ; individuals with intermediate colors and forms between the species are commonly identified. Chromosomal analysis and DNA amount showed a uniform population. Regardless of the aspects related to the color and shape of floral structures, all individuals presented 2 n = 96 chromosomes and an average of 14.05pg of DNA. Irregularities in meiosis associated with chromosome number and C value suggest the occurrence of polyploidy. The genetic distance estimated using ISSR molecular markers revealed the existence of genetic variability, not related to morphological clusters. Morphometric measurements of the flower pieces revealed that Z. maculatum has greater variation than Z. triste but without a defined circumscription. The observed variation can be explained by the polyploid and phenotypic plasticity resulting from the interaction of the genotypes with the heterogeneous environments observed in the study area. The data together contributed to the understanding of evolutionary processes and the origin of diversity in tropical regions.