Leaf Anatomic Structure and Cold Tolerance Evaluation of 6 <i>Nymphaea</i> Species

10 leaf anatomical indexes of 6  Nymphaea  species were observed and measured, and the cold tolerance was evaluated by cluster analysis and membership function. The result showed that  Nymphaea  is of bifacial leaf, stomata are only distributed in upper epidermis, and the thickness of upper epidermis was smaller than that of lower epidermis. Leaf thickness has significant differences and  Nymphaea  potamophila  had the most compact leaf structure while  N.alba  had the most loose. Through cluster analysis, 10 indicators were divided into 3 categories, and indicators with the largest correlation coefficients were leaf thickness, stomatal density andpalisade tissue-spongy tissue ratio, which were found to be the main factors to evaluate the cold resistance of different  Nymphaea  species. The order of the six species based on cold tolerance from strong to weak is  N.alba ＞ N. potamophila ＞ N.lotus ＞ N.immutabilis ＞ N.colorata ＞ N.minuta .