Anatomy Of Three Species Of Hydrocharitaceae In Northeastern China And Note On Taxonomic Implication

The structure of Hydrocharis dubia, Ottelia alismoides, Hydrilla verticillata in thefamily Hydrocharitaceae in northeastern China were studied in the thesis using GMAsemi-thin section method. The reproductions of Hydrocharis dubia and Otteliaalismoides were observed and recorded in detail.The adventitious roots of Ottelia alismoides and Hydrilla verticillata have nolateral roots and their root hairs are rare, but both are present in Hydrocharis dubia androot hairs are rich. The aerenchyma and reduced vascular tissue occur in roots and stemsof the three species. The small peripheral vascular bundle is present in stems ofHydrocharis dubia and Ottelia alismoides, but lacking in Hydrilla verticillata which hasone large central vascular bundle. The paracytic stoma was observed on the epidermisof Hydrocharis dubia leaves which have honeycomb-like aerenchyma in abaxile. Thepalisade and spongy tissues are differentiated in its mesophyll and main vein is withdeveloped vascular bundle. Ottelia alismoides and Hydrilla verticillata have equifacialleaf and in which the aerenchyma or intercellular space are present, but palisade andspongy tissues are not differentiated in the mesophyll.The sepals and petals of Hydrocharis dubia and Ottelia alismoides are composedof epidermis, ground tissues and vascular bundles. The stoma was observedoccasionally in sepal of Ottelia alismoides. Sepal and petal of Hydrilla verticillataconsist of2-layer epidermal cells. In its female flower, some parenchyma cells existbetween2-layer epidermal cells. The Ottelia alismoides fruit enveloped by spathe, sixcarpels combine with each other, and their edges don’t connect each other completely inthe center of the fruit. Hydrilla verticillata fruit consists of3carpels connected eachother and has ovary inferior with parietal placenta. Ottelia alismoides seeds havelignified seed coat. The outermost seed coat of Hydrilla verticillata has starch grains inthe early development, outer tangential wall depressed after mature without starch grain.Seed embryos of Ottelia alismoides and Hydrilla verticillata have starch grains.Hydrocharis dubia sexual reproduction, the seed after germinating, could onlyform a seeding with5or6leaves, and then stop growing and die gradually. Thevegetative propagations mainly include turions and clones plants. Ottelia alismoides only has sexual reproduction. During the process of seed germination, hypocotylelongates, the ring-shaped protrusion at the terminal of the hypocotyl, unicellular hairsdevelop. After4-5adventitious roots occur, primary root die gradually.The morphology of three species of Hydrocharitacea in northeastern China werestudied, the similarities and differences among three species， recognizing themorphology and structure adapt to the aquatic environment and the reproductions. Thestudy completes the botanical research of Hydrocharitaceae and provides the importantmorphological basis to explore the relationship among Hydrocharitaceae, Alismataceaeand Butomataceae.