Based on flow cytometry measurements, the expected genome size for an average tetraploid hybrid was approximately 9 pg. The vast majority of the putative F1 hybrid plants (166 out of 187) exhibited flow cytometry readings near this value, indicating that these are likely true interspecific hybrids (Fig. 1). However, 21 putative F1 hybrids (12.2%) had DNA content equal or greater than the reported 1 C genome size for H. tuberosus (12.55 pg). We inferred that these plants were hexaploid, resulting from either self-pollinated or intermated H. tuberosus plants. These plants were excluded from further analysis.