Key to the Orders 



In the Keys, asterisks indicate orders, famihes, genera, or species 

 that are hkely to be found in the central Great Lakes region but 

 have not been reported there to date. 



1. Motile in the vegetative condition; flagella 2 or 4, rarely 8, equal in 

 length; organism 1-celled or colonial volvocales 



1. Not mo':ile in the vegetative condition... 2 



2. Cells embedded in copious mucilage (which is either homogeneous or 

 lamellated), imited in colonies of indefinite shape (see Apiocystis, 

 however), or in tubes forming gelatinous strands ( pseudofilaments ) , or 

 bullate masses (See mucilage-invested Chlorococcales also.); some 

 forms unicellular or forming dendroid colonies which are epiphytic 

 or epizoic; cells frequently possessing false flagella ( pseudocilia ) , 

 returning to a motile condition without resorting to reproductive 



cells TETRASPORALES 



2. Plants not as above 3 



3. Plants filamentous, composed of cells adjoined end to end in definite 

 series, sometimes interrupted 4 



3. Plants not composed of cells arranged to form filaments; unicellular or 

 colonial or, if filamentous, occurring as coenocytes vvdthout cross walls 15 



4. Filaments unbranched; attached or free-floating 5 



4. Filaments with branches, the branches sometimes closely appressed, form- 

 ing pseudoparenchymatous masses. 13 



5. Filaments composed of a single series of cells 6 



5. Filaments composed of more than 1 series of cells; cells adjoined; thallus 



a hollow tube or a ribbon-Uke or frond-like expansion 12 



6. Chloroplasts 1 to several, large, in the form of spiral bands, stellate 

 masses, or broad plates; pyrenoids conspicuous; reproduction by conjuga- 

 tion .- - ZYGNEMATALES 



6. Chloroplasts parietal, plate-like, net-like, or small and ovate ( in the latter 

 case usually many in a cell); reproduction by iso- or heterogametes 7 



7. Cells witli a single, parietal, plate-like or broadly discoid chloroplast; 

 cells cylindrical; filaments uniseriate or multiseriate ulotrichales 



7. Cells wdth other types of chloroplasts 8 



8. Plants composed of long, cylindrical, coenocytic and thin-walled units, 

 containing numerous disc-like chloroplasts arranged in narrow annular 

 bands; cross partitions with knob-like thickenings; reproduction usually 

 oogamous sphaeropleales 



8. Plants not as above 9 



9. Cells cylindrical, ovate or subspherical, each surrounded by lamellate 

 mucilage; frequently losing their uniseriate arrangement and forming 

 palmella stages; chloroplast massive, filling the cell, obscured by many 

 starch grains; sexual reproduction oogamous cylindrocapsales 



9. Cells cylindrical, not surrounded by lamellate mucilage; chloroplast 

 parietal 10 



10. Cells with parietal, net-like or sheet-like chloroplasts, which usually cover 

 both the end and lateral walls; wall composed of two sections which over- 

 lap in the midregion, forming H-shaped pieces upon fragmentation; 

 pyrenoids lacking; sexual reproduction unknowm .microsporales 



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