Submitted to: American Journal of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2004
Publication Date: 8/22/2005
Citation: Woods, K., Hilu, K.W., Wiersema, J.H., Borsch, T. 2005. Pattern of variation and systematics of Nymphaea odorata: I. Evidence from morphology and inter-simple sequence repeats (ISSRs). Systematic Botany 30:471-480. Interpretive Summary: Waterlilies are among the most beautiful aquatic plants cultivated by horticulturalists. Although studied for decades, there is still disagreement about the species of the waterlilies that exist in North America. With the use of molecular tools, it is possible to determine relationships among these aquatic plants and compare the results with their morphological characteristics. Sequence data from a region of the genome of waterlilies were used to determine if the two species of waterlily in North America are distinct. These data suggest that what some botanists have regarded as two species with widely varying morphological characteristics is actually just one variable species that has two subspecies. This research will be used by botanists to accurately describe and name waterlilies in North America.
Technical Abstract: Nymphaea odorata is the most widely distributed water-lily in North America. Disagreement exists on whether this morphologically quite variable species should be split into two species, N. odorata and N. tuberosa, or treated as one species with two subspecies. Morphological characters and markers from the inter-simple sequence repeats (ISSRs) were examined to assess taxonomic status and elucidate patterns of genetic variation among populations. This study provides evidence against treatment of N. tuberosa at species rank. The principal component analysis of 26 vegetative characters although underscoring immense variability, does partially segregate populations of subsp. odorata and subsp. tuberosa. Based on analysis of variance, a new set of morphological characters is proposed to discriminate between the two subspecies: mean leaf blade length to width ratio, petiole striping and lobe apex shape. Results from ISSRs show high polymorphism within and among populations. Genetic variation was found largely within geographical regions (89%) rather than among regions. Principal coordinate analyses and minimum spanning tree based on ISSRs clearly distinguished Nymphaea mexicana and N. odorata. Within N. odorata, subsp. odorata appears as a distinct entity, whereas samples of subsp. tuberosa had some samples linked to subsp. odorata samples. This inter-subspecific variation may be due to gene flow among populations.