The reproductive biology and genetic diversity of Potamophila parviflora R. Br

Potamophila parviflora, a wild relative of domestic rice, is endemic to the north-eastern river systems of New South Wales, Australia. It is the only member of the genus,and is habitat specific. Several new sites were found, mostly in the Upper Clarence catchment. Florets of P. parviflora were found to be 86% female-only, while 14% contained mature male reproductive parts, which occurred more often in the middle sectionof the panicle. Pollen was found to be necessary for the developmentof mature fruits. RAPD data showed that there is very little genetic variation between individual plants, or between different populations. An embryological study showed several irregularities in megasporogenesis and megagametogenesis. No tetrads were observed in megasporogenesis and the ovule is vacuolate at the megaspore mother cell stage. Megagametogenesis proceeded rapidly, nuclei within the ovule were sometimes not spherical and varied in size, and sometimes the antipodal cells doubled in number with a corresponding halving insize of the nuclei. Chromosome number varied between 2n = 24 and 2n = 25, between and within populations. These results indicate that P. parviflora could be a diplosporous apomict of the Antennaria type, although further works are required to provide conclusive proof.