Aponogeton is a genus, or related group, of around 50 species of aquatic flowering plants. Aponogeton species are native to Africa, Europe, South America and Australasia. Some species are kept as ornamental plants in ponds and aquariums, and some are threatened by collectors who ruthlessly harvest them in great numbers. Invasive aquatic weeds and pollution also play a part in threatening the survival of some species in their natural habitat.
Aponogeton species are usually cyclical plants in their natural habitat. The growth of vegetation usually occurs from March to May. Flower production follows the vegetative growth in May and June, after which seed production occurs in June and July. The tubercle stores nutrient reserves from August to October, and then sheds its leaves to enter a dormant phase. The tuber remains dormant until conditions are correct for the growth process to begin again.
To imitate the cyclical nature of the aponogeton life cycle in an aquarium, an enthusiast must reduce the temperature of the aquarium to between 46 degrees Fahrenheit (8 degrees Celsius) and 50 degrees Fahrenheit (10 degrees Celsius) in October. In February or March, the temperature of the aquarium should be raised to between 64 degrees Fahrenheit (18 degrees Celsius) and 68 degrees Fahrenheit (20 degrees Celsius) to stimulate new growth. This is not always practical, especially if there are other organisms in the aquarium that cannot tolerate such temperatures. Another method involves placing the leafless tuber and some aquarium water into a refrigerator for two to three months, after which the tuber can be returned to the aquarium to stimulate new growth.
Aponogeton bullosus is native to Australia, where it is considered endangered and is a high priority for conservation and protection. Like most varieties of aponogeton, the bullosus grows from a tubercle. Tubercles are a bulb high in starch, similar to a potato, which stores energy and nutrients for the plant to utilize throughout its life cycle. Aponogeton is often able to survive periods of drought, because the tubercle goes dormant until suitable growing conditions are present again.
Bullosus is a perennial plant that grows in fresh water. This species prefers cool, fast flowing fresh water with granite sand. The flower of the bullosus is a large cone-shaped, yellow spike on stems measuring between 3 inches (8 cm) and 12 inches (30 cm).
Another aponogeton species that is endangered in its natural habitat is madagascariensis, more commonly known as the Madagascar laceleaf. This species is native to Madagascar and is a very popular aquarium plant with tuberous roots that are edible. The Madagascar laceleaf requires bright light to grow, which causes algae to grow on the water and on the leaves of the plant. This makes cultivation of this species difficult and unpredictable. It requires fast flowing water at temperatures between 59 degrees Fahrenheit (15 degrees Celsius) and 78 degrees Fahrenheit (26 degrees Celsius) with a pH of 5 to 7.