HALORAGALES

the water milfoil order of dicotyledonous flowering plants comprising two families and seven genera of remarkably diverse aquatic and terrestrial herbs distributed throughout the world. The plants are characterized by their herbaceous habit and simplified flowers, which often lack petals and have a one- to four-chambered ovary that is positioned below the attachment point of the other floral parts and contains only one ovule per chamber. The flowers are wind- or water-pollinated. The order is considered to be related to the myrtle order (Myrtales) and to have an ancestry with it in the order Rosales. The larger group is the water milfoil family (Haloragaceae, or Haloragidaceae), some 150 species of land, marsh, and water herbs with small leaves, small flower clusters, and flowers with a two- to four-chambered ovary and a similar number of styles (pollen-receptive parts at the upper end of the ovary). The genera are Haloragis (75 species), Myriophyllum (45 species), Laurembergia (22 species), Proserpinaca (4 species), Loudonia (3 species), and Meziella (1 species). Of these, only one provides plants of horticultural interest, the water milfoils (q.v.; Myriophyllum). The family Gunneraceae, almost entirely found in the Southern Hemisphere, contains one genus, Gunnera, with about 50 species of large terrestrial herbs, many of which have huge, long-stalked leaves with round or kidney-shaped blades that give the plants a rhubarb appearance, but the leaves may be as much as 3 m (about 10 feet) across the blade. Often grown as a striking garden ornamental, for example, is Gunnera chilensis, which has clusters of green leaf stalks nearly 2 m long. The stalks are covered with stiff, bristly hairs and topped by large round or heart-shaped leaf blades with deep lobes radiating from the attachment point of the stalk. A similar but even larger species (G. manicata) has leaves that are attached at the centre of the blade.