Phylogenetic reconstruction of the genus Tephrocactus (Cactaceae) based on molecular, morphological, and cytogenetical data

Tephrocactus comprises species mainly endemic to Argentina. Molecular phylogenetic analyses of all proposed species of the genus as well as classical (chromosome number, karyotype) and molecular cytogenetical techniques (DNA content, heterochromatin amount, rDNA genes) were conducted. Sequence data of two plastid DNA markers of Tephrocactus taxa were analyzed. Evolution of character states of cytogenetical and morphological (growth form, presence of leaves, glochids and tepal spiny mucrons, flower color) traits were reconstructed. Species show x = 11 with different ploidy levels (2n = 22, 44, 66, 77, 242, 319), small chromosomes, and symmetrical karyotypes. Tephrocactus was recovered as monophyletic with three main clades including 12 species, using molecular and morphological data. Tephrocactus geometricus, T. halophilus, and T. paediophilus are recognized as distinct species. Banding patterns showed CMA⁺/DAPI⁻ constitutive heterochromatin associated with nuclear organized regions. Heterochromatin amount ranged from 2.99% to 6.50%. The 18S-5.8S-26S ribosomal DNA (rDNA) sites coincided with the CMA⁺/DAPI⁻ signals. The 5S sites varied with ploidy levels of the taxa. DNA content (2C = 1.99–24.50 pg) had a significant and positive correlation with ploidy level and the number of rDNA genes. The ancestor is reconstructed to have been a dwarf shrub with strong articulation, glochids, and deciduous leaves, white, pink or pearly tepals without spiny mucrons, 2n = 22, low DNA content, and one pair of each rDNA gene followed by three polyploidization events. Tephrocactus diversification has been associated with polyploidy and few cumulative small cryptic chromosomal changes.