to a starch test and has lost the long attenuated filament tips typical 

 of the genus. Consequently, no representatives of the Rhodophyta have 

 been identified from the Yellowstone or its tributaries as reported 

 previously. 



The frequency at which diatoms and the non-diatom taxa appeared 

 in the Yellowstone River samples is shown in Table 1. Diatoms appeared 

 in all samples while Cladophora glomerata occurred in about three- 

 quarters of all samples. Other major taxa, in descending order of 

 frequency, were Oscillatoria (59.4%), Ulothrix (40.0%), Stigeoclonium 

 (26.4%), Closterium (25.6%), Cosmarium (20.5%), Scenedesmus (15.4%), 

 Phormidium (13.8%), and Spirogyra (13,4%). Most taxa appeared in the 

 plankton at roughly the same frequency they appeared in the periphyton. 



The frequency at which diatoms and non-diatom genera dominated 

 Yellowstone River samples appears in Table 2. Diatoms dominated half 

 of all samples collected. Although many non-diatom algae occurred 

 frequently as shown in Table 1, only one-- Cladophora glomerata -- 

 was consistently abundant as well as present in the Yellowstone samples, 

 In fact, C. glomerata was more frequently the dominant taxon in peri- 

 phyton samples than were diatoms. In most cases where diatoms were 

 dominant, C. glomerata was a close second, and vice versa. Only five 

 other non-diatom taxa were ever dominant and all were dominant in- 

 frequently. 



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