Vegetative reproduction is carried on by fragmentation and in 

 one genus, Pithophora, by large akinetes. Sexual reproduction is by 

 biflagellate isogametes, usually produced in large numbers in the 

 terminal or subterminal cells of the branches. Biflagellate zoospores 

 are common, especially in Cladophora. There is one family. 



FAMILY CLADOPHORACEAE 



Characteristics as described for the order. Plants branched, either 

 regularly or irregularly, although in a few species branches are rare 

 or wanting. Attached feathery tufts in either flowing or quiet water, 

 or occurring as free-floating mats. 



Key to the Genera 



1. Filaments growing on the backs of turtles; 



branching only from the base Basicladia 



1. Filaments not growing on the backs of turtles; 



branching or not branching 2 



2. Filaments not branching Rhizoclonium (in part) 



2. Filaments branching 3 



3. Filaments repeatedly branched and showing distinct basal-distal 

 differentiation in the habit of branching; branches gradually 



attenuated toward the apices; akinetes lacking Cladophora 



3. Filaments not repeatedly branched, not clearly showing basal-distal 

 differentiation, akinetes sometimes present 4 



4. Filaments branching irregularly; enlarged 



akinete cells frequent Pithophora 



4. Filaments branching irregularly; akinetes wanting 5 



5. Branches short and rhizoidal, mostly 



1- or few-celled Rhizoclonium (in part) 



5. Branches long, multicellular - 6 



6. Branching sparse but rather regular, the branches mostly diverging 

 dichotoniously, or oppositely Old, floating thalli of Cladophora 



6. Branching frequent, irregular, the branches mostly at right angles to the 



main axis, scarcely attenuated toward the apices .— Rhizoclonium ( in part ) 



CLADOPHORA Kuetzing 1843, p. 262 

 A repeatedly-branched filamentous thallus with basal-distal dif- 

 ferentiation; attached when young but in some species becoming 

 free-floating; forming feathery tufts on substrates, especially in 

 flowing water; branching alternate, opposite, or sometimes di- or 

 trichotomous, the branches smaller than the main axis, or at least 

 tapering slightly toward the apices; cells cylindrical or swollen; 

 walls thick and lamellate in most species, sometimes thin and firm; 

 chloroplast a parietal reticulum which sometimes becomes frag- 

 mented and appears as numerous discs; pyrenoids present; asexual 

 reproduction by zoospores; sexual reproduction by isogametes 

 produced in apical or subapical, unspecialized cells. 



[135] 



