Distribution Pattern and Morphological Diversity of Trapa L. in the Heilong and Tumen River Basin

Considerable disagreements about the classification system of Trapa L. still exist, with no current unified view. The Amur River and Tumen River basin is an important species distribution and diversity center of Trapa. To reveal the geographical distribution pattern and morphological diversity of Trapa plants in this basin, we conducted field surveys and research. We found 11 species and 8 types of intraspecific variability from 28 lakes in the area, indicating that Trapa exhibited rich morphological diversity. In addition, 354 Trapa specimens were also consulted and a total of 92 distribution data locations were obtained. The geographical distribution pattern of the 11 species was not balanced. The distribution of Trapa maximowiczii Korsch.was the widest, while Trapa incisa Siebold et Zucc., Trapa khankensis Pshennikova, and Trapa kozhevnikovirum Pshennikova showed narrow domain distribution. The Eastern Ussuri River and Tumen River basin was found to be the diversity distribution center of Trapa, and might be a Quaternary glacial refuge. Interspecific morphological features of Trapa were relatively stable. Trapa manshurica Fler., Trapa potaninii V.Vassil., Trapa japonica Fler., Trapa sibirica Fler., and Trapa maximowiczii Korsch.exhibited eight intraspecific variabilities. Most morphological characters were stable within the population, whereas variabilities were obvious between populations. The diffusion limit of gene flow was an important factor resulting in the imbalanced distribution patterns and intraspecific variability of Trapa. This research lays the foundation for clarifying Trapa classification. Based on the results, combined with molecular marker technology, studying the phylogenetic relationships could have significant impact in revealing the evolutionary history of the Trapa genus.