Fig. 1. Estimated values of 2C nuclear DNA content for the ten accessions of cultivated oca measured on different days, using either CRBCs or rice leaves as internal standard (0·87 pg/2C used as value for rice standard). The day‐to‐day variation (e.g. between samples run on 6 April and those run on 30 March) was greater for the cultivated O. tuberosa accessions than for wild Oxalis samples, for unknown reasons, but did not depend on the standard used. Only the values from 6 Apr. 1999 are shown in Table 3, because only on that day were all ten samples measured. The mean value of all oca accessions measured on that day is 3·610 pg/2C (s.d. = 0·061), whereas the mean for all days is 3·514 pg/2C (s.d. = 0·116) and the mean of those using rice leaves as internal standard was 3·524 pg/2C (s.d. = 0·066).