Superorder Alismatiflorae

Abstract

Herbaceous aquatic, semi-aquatic and marsh plants, some growing even in marine waters, which is unique in the angiosperms. The root hairs are developed from epidermal cells shorter that the ordinary epidermal cells (Leavitt 1904). Starch-rich rhizomes occur in several families but bulbs, corms and tubers are rare. Hibernacula occur in certain groups. The leaves are alternate or opposite. They may be uniformly linear and ribbon-like or differentiated into petiole and lamina. The veins in the former kind of leaf are parallel, those in the latter are arching and converging at the apex. Sparsely reticulate or transverse veins may occur. The leaf base is usually sheathing and invests the stem loosely. Stipules are present in various Zosterales and a few Alismatales (Hydrocharitaceae), and form the so-called “lingular sheaths” in the Potamogetonaceae. Intravaginal scales (or “squamules”) are almost diagnostic to the superorder (Arber 1923; von Staudermann 1924; Tomlinson 1982).