Aiming to analyze the evolutionary relationships between the diploid species Turnera grandiflora (2n = 2x = 10) and the octoploid T. fernandezii (2n = 8x = 40), inter-specific hybrids were recovered by in vitro embryo rescue methods. The full-grown plants obtained were all pentaploids (2n = 5x = 25) confirming their hybrid nature. The chromosome associations observed in the hybrids during meiosis were indicative for an autopentaploid, suggesting that T. fernandezii carries the genome of T. grandiflora (C^gC^g) but at the octoploid level (C^gC^g C^gC^g C^gC^g C^gC^g). This fact confirms a close evolutionary relationship between the species and supports the hypothesis that T. grandiflora is the progenitor of T. fernandezii. A tentative hypothesis regarding the autopolyploid origin of T. fernandezii is finally formulated.