A haploid (2x = 24) plant was obtained from a cross between O. minuta and O. eichingeri. It was morphologically similar to, but smaller than, O. minuta. Chromosomes varied in length from 1.1 to 2.6 mu . Constrictions were median in eight chromosomes, either median, submedian or subterminal in three chromosomes, and submedian or subterminal in the remaining one. Three chromosomes had satellites and two had secondary constrictions. At meiosis, pairing in pachytene cells was generally disordered or incomplete although one cell with complete pairing was found. At metaphase I/anaphase I, an average of 1.09 bivalents occurred. It is postulated that a gene which suppressed pairing between two sib genomes arose when an autotetraploid developed from diploid Philippine O. officinalis. This autotetraploid is considered to be the progenitor of O. minuta.