GROWTH AND REPRODUCTION
GROWTH

The specific growth rates for duckweed are very high, resembling bacterial growth, ranging from 0.1 to 0.35 g/g-day (Oron et al., 1986). The variables that directly affect the growth of duckweed are listed below. To learn about their reproduction, click here.


pH


Duckweed can tolerate a wide pH range, but survives best between pH's of 4.5 to 7.5. pH values greater than 10 will have serious effects on growth, and can limit the cover capacity across a pond or water body. A diurnal pH of 10 is possible in ponds only partially covered with duckweed because of algal activity (Zirschky, 1988).

Light and Temperature


Duckweeds can grow in full sunlight as well as dense shade. Optimum growth is determined to be between 20 and 30 degrees Celcius, although serious effects will occur with temperatures ranging from between 35 to 40 degrees Celcius (Zirschky, 1988). They are more cold tolerant than other aquatic vascular plants, and can sustain temperatures as low as 7 degrees Celcius for normal, practical growth. Under freezing conditions, duckweed will lay dormant on the pond bottom until warmer conditions return. A full, thick mat of duckweed may have a temperature of about 10 degrees above ambient air conditions due to radiation (Buddhavarapu,1991).

Pollutants


High metal concentrations will inhibit certain species of Duckweed growth, as well as PCB's, and ethylene. Growth will also be inhibited by nitrogen deficient wastewater or by filamentous algae or fungus (Zirschky, 1988).

Wind and Wave Movements


Wind and wave action can impede duckweed growth and stabilization by disrupting their ability to attach themselves to each other and form their characteristic homogenous colonial populations. Optimal conditions for growth are quiet streams and ponds (Daubs, 1965).


REPRODUCTION

S. Polyrhiza attached together!!

Reproduction of duckweed is one of the fastest rates recorded, presumably at least twice that of other vascular plants!

The reproduction of the duckweed is chiefly by budding from a single basal pouch or two lateral pouches. It has been observed that many generations can stay attached to the short stipes of the host plant. A small cell in the frond divides and produces a new frond, and each new frond can reproduce at least 10 to 20 times during its life cycle of about 1-2 months (Zirschky, 1988).
Although flowering is infrequent in some species, all duckweeds bloom and reproduce sexually. The flowers are typically protogynous with the stigma receptive before the anther is mature, therefore, the plants must be cross pollinated by genetically different individuals with mature pollen-bearing anthers in synchronization with the receptive stigmas. During the summer months, 2 stamens and 1 pistil, all enclosed in a membraneous saclike spathe, appear within the budding pouches at the edge of the plant body in Lemna and Spirodela, wheras, in Wolffia and Wolffiella, a minute floral cavity develops on the upper side of the plant body containing a single stamen and pistil (Armstrong, 1996).



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