Nonindigenous Aquatic and Semi-Aquatic Plants in Freshwater Systems

Nonindigenous Aquatic Plants

Water Spinach (Ipomoea aquatica) Forsk.

The first historical record of water spinach (Fig. 19) is of its cultivation as a vegetable during the Chin Dynasty about 300 A.D. (Edie and HO 1969). Its native origin is Southeast Asia and India. Its introduction into Florida is unclear; however, Ochse (1951) reported that water spinach grows well in winter and summer in the Everglades. Water spinach is popular among persons of Asian descent in Florida. The species has become Florida's most problematic non-naturalized noxious weed species. The species is cultivated as an edible vegetable by Asian immigrants for personal use and for sale in oriental food markets throughout the United States. It is a vine-like species that can grow in a wide range of habitats and is quite aggressive in Florida's water bodies because of its prolific growth rate. The Florida Department of Natural Resources seized seeds and harvested plants from Oriental food stores and destroyed many water-spinach infestations in southern and central Florida drainage ditches and ponds. Many believe that establishment of the species in Florida is only a matter of time. Most occurrences of water spinach in the wild are deliberate plantings. They are usually confined to ditches and pond shores; however, water spinach has been discovered in two public lakes, West Lake Tohopekaliga and Lake Maggiorie (Schardt and Schmitz 1990).

Water spinach is a perennial trailing herb of muddy stream banks and freshwater ponds and marshes. It is confined to the tropics and subtropics because it is susceptible to frosts and does not grow well where mean temperatures are below 23.9 C (Edie and Ho 1969). It usually grows prostrate but can climb and cover emergent vegetation.

Although water spinach had not been in public lakes or rivers until 1990, its possession in Florida has been prohibited since 1973. The greatest management concern is its adaptation for growth in areas of periodic drying and flooding such as the Everglades. This concern is heightened because water spinach is a climbing vine that can grow to 10 cm/day. Furthermore, attempts to control water spinach with registered aquatic herbicides were only temporary. Diuron provided acceptable control in dry ditches but also controlled most other adjacent plants, which is unacceptable in areas such as the Everglades (Schardt and Schmitz 1990). Because of its prolific growth, this species can invade moist cultivated areas, such as rice and sugar cane fields, and other areas with varying water levels, such as the Everglades, drainage canals, and ditches. A single plant of Chinese water spinach may grow taller than 21 m and can branch profusely. Harvesting by humans and wildlife creates fragmentation (Schardt and Schmitz 1990).