486 AQUATIC PHYCOMYCETES 



Physoderma lycopi Sparrow 

 Amer. J. Bot., 44: 664, 26 figs. 1957 

 On Lycopus americanus. 



Operculatae 

 CHYTRIDIACEAE 



Thallus epi- and endobiotic, monocentric, eucarpic, the epibiotic 

 part either expanding and becoming an operculate sporangium and the 

 endobiotic part forming the vegetative system, or not enlarging and 

 forming an evanescent cyst, and the endobiotic part then forming the 

 reproductive organs as well as the vegetative system, occasionally 

 interbiotic; zoospores produced in the sporangium, posteriorly uniflag- 

 ellate, generally with a single globule, released upon the dehiscence of 

 the operculum; sexual reproduction, where known, by fusion of aplan- 

 ogametes; resting spore inter-, epi-, or endobiotic, upon germination 

 producing an epibiotic sporangium. 



Parasites and saprophytes of fresh-water and marine algae, also of 

 other Phycomycetes, pollen, and Protozoa. Members of the Chytrid- 

 iaceae, with the inoperculate families Phlyctidiaceae and Rhizidiaceae, 

 make up the majority of the "chytrids." They include the operculate 

 counterparts of the other two groups, also monocentric, and exhibit 

 a remarkable parallelism in body form. Species of Chytridium (the 

 largest genus) with apophyses and those with unbranched rhizoidal 

 systems have never been segregated into distinct genera as have like 

 forms in the Phlyctidiaceae. 



KEY TO THE SUBFAMILIES AND GENERA OF THE CHYTRIDIACEAE 



Sporangium epi- or interbiotic, formed from the body of the encysted 

 zoospore or as a lateral outgrowth of the main axis, external to 

 substratum; resting spore endo-, epi-, or interbiotic 



Subfamily Chytridioideae, p. 488 

 Sporangium developing from all or part of the expanded body of the 

 encysted zoospore, external to the substratum; parts variable 

 in size 

 Rhizoidal system arising from one place on the base of the spo- 

 rangium; the latter with a single discharge papilla 



