**2. Biology of water hyacinth**

The WH, a large, free-floating aquatic weed found either on the surface of fresh waters or anchored in mud, is a tropical aquatic plant with attractive purple flowers, 10–15 cm wide and bright, shiny green leaves on long petioles. The mature WH consists of roots, stolons, petiole, leaves, leaf isthmus, peduncle of the flower spike, inflorescence, adventitious roots, daughter plants, and fruit clusters (see **Figure 2**) [32, 33]. The root morphology is highly plastic and fibrous, having one single main root with many laterals, forming a huge root system. Because each lateral root has a root tip, WH may exploit nutrients in a low-nutrient water body, which makes the lateral roots longer and denser at low phosphorus concentrations [33]. It can replicate both sexually by seeds and asexually by vegetative implying budding and stolen

**Figure 2.** *Morphology of WH plants with stolons.*

generation [32]. Both reproduction systems have a large production potential, within a very short period of time. The uniparental reproduction system happens through vegetative reproduction. In vegetative reproduction, 3.42 million plants can be produced in about 200 days and 43 daughter clusters of leaves in 50 days [32]. Threeparent plants can deliver up to 3000 new growing plants in 50 days, and two-parent plants can provide up to 30 offspring after 23 days. The sexual reproduction of the weed is through the production of seeds from its flowers by the agents of insects. Single WH plant can give flower in 26 days. The seed spread can be through a number of mechanisms including humans and the legs of birds [33]. Propagation by seeds may contribute to the spread of WH and can be a potent source of reinfestation [32].

Some authors report weight gains of 4.8% per day and the number of WH plants doubled on average every 13 days in a field observation [6]. It can grow most rapidly in water temperatures from 28 to 36°C [16] and at a pH from 4 to 8 [5]. They cease to grow when the water temperature is above 40°C or below 10°C, and the pH range for growth is between 4 and 10. The height of the plant can reach up to 1 m above the water surface, but its common height is 20–30 cm. The stalks are long, spongy, and bulbous. The roots are freely hanging on elongated treads with purple-black color and 2.54 cm underneath the water surface. The leaves of the weed have purple and yellow spots. Under favorable conditions, its biomass can reach up to 25 kg/m<sup>2</sup> or 300–442 tons/ha, 500,000 plants/ha, each flower can produce up to 400 seeds and a plant up to 5000 seeds [32]. In the tropics, it has been found a duplication of the population every 7 days and annual productivity of between 930 and 2900 tons/ha [34]. The seeds can live up to 15–20 years in water, silt, and mud [32, 35]. With these characteristics, the WH has become a major ecological and economic problem in this century in the tropics and subtropics [5, 16].
