Insights into distyly and seed morphology of the aquatic plant Nymphoides fallax Ornduff (Menyanthaceae)

Nymphoides fallax is a distylous tetraploid species, endemic to Mexican and Guatemalan highland wetlands. Two floral morphs have been previously reported for N. fallax, but no studies have quantified floral organ variations and seed viability. Here we describe the reproductive system and seed morphology, compare measurements of short-and long-styled flowers, and test seed viability. We studied flowers, fruits, and seeds using light and scanning electron microscopes. Morphs differ in sepal, petal, corolla tube, filament, anther, pollen, pistil, stigma, and stigmatic papillae size. Further differences include stigma and stigmatic papillae shape. Morphs have similar ovule and seed number, and the studied population is nearly isoplethic. Fruit and seed production was high, as was seed viability (86 %). We noted prominently projecting tubercles and caruncles not previously reported for N. fallax seeds. Seeds float on the water surface and seedlings are established in the field. Even when studies of other populations are needed, our findings suggest that sexual reproduction and intra-morph incompatibility may play a substantial role in this aquatic plant, although it is capable of strong vegetative reproduction. Understanding the role of distyly can contribute to elucidate N. fallax reproductive biology, and to establish conservation practices for the species and wetland ecosystems.