GIANT PONDWEED 



Potamogeton vaginatus Turcz. 



This pondweed is undoubtedly often mistaken for the large 

 vigorous form of sago pondweed that is commonly referred to as giant 

 sago pondweed. Incorrect identification of this plant can be easily 

 made because its vegetative growth characteristics are similar to those 

 of sago. Only close examination can differentiate the two plants The 

 stems of giant pondweed are freely branching and leafy. All the leaves 

 are submersed and are narrow-linear in shape. In general, though, the 

 leaves and stems of this species are larger and more robust than those 

 of sago. 



There are a number of vegetative characteristics of this species that 

 can be observed which can be used to differentiate it from other 

 pondweeds with generally similar vegetative character. Like many 

 organisms in nature, some of the identifying features given for giant 

 pondweed can vary from those illustrated in this booklet. One of these 

 which typifies the situation is the loose, leaf-sheathlike structure or 

 stipule produced on the lower or primary leaves (insert 1 ) of giant 

 pondweed; botanical descriptions indicate that this characteristic is 

 sometimes approximated in sago pondweed. The leaf tips of giant 

 pondweed are rather blunt and sometimes slightly notched (insert 2), 

 unlike the sharp, tapering tip of sago. Flowering spikes of giant 

 pondweed are more numerous and in more crowded whorls than those 

 found on sago. 



One feature that should aid materially in the identification of this 

 species is the uniquely shaped tuber, which is much different than the 

 sago tuber (insert 3). These tubers are produced in knotty clusters on 

 the terminals of fleshy white underground stems. 



A third pondweed species, P. filiformis, is closely related to both 

 giant and sago pondweed and could be mistaken for giant pondweed. 

 In general, P. filiformis, or fine-leaved pondweed, is less vigorous and 

 has smaller leaves, stems, and tubers, although the tubers are similar 

 to those produced by P. vaginatus. 



Giant pondweed is seldom reported in Western irrigation systems, 

 but probably occurs more often than suspected because of its similarity 

 to the cosmopolitan sago pondweed. 



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