Wilson: North American Peronosporales 169 



Rhysotheca Acalyphae sp. nov. 



Hypophyllous, forming a dense or very sparse, whitish growth 

 on the host, epiphyllous discoloration prominent, yellowish to dark- 

 brown, appearing to cause dead spots on the leaves, often accom- 

 panied by a pronounced tinge of red on the under side of the 

 leaf ; conidiophores solitary or only 2 or 3 from a stoma, 300- 

 500 X 5-7 4-5 times branched, forming a loose, open head of 

 about T /2 to Yz the total height, branches elongate, straightish, 

 branchlets sometimes at a very small angle, ultimate branchlets 

 straight, slightly flexed, short, 4-10 fi long, more or less conic and 

 broadly truncate; conidia brownish, ovoid to globose, 12-22 X 

 10-16 /x; oospores not seen. 



The type on Acalypha virginica L., Madison, Wisconsin, Sept. 

 30, 191 5, T. T. Davis. 



This species is not to be confused with any other on euphor- 

 biaceous hosts, as the others are all undoubted members of the 

 genus Peronospora. Its nearest ally is R. illinoisensis (Far low) 

 Wilson, from which it differs in its more pronounced discolora- 

 tion of the host ; the larger conidiophores, which branch more ; 

 and the shorter apical branchlets. The conidia are very similar, 

 both in size and form. It is also quite similar to R. australis 

 (Speg.) Wilson, from which it differs in having more delicate 

 conidiophores and larger conidia. The apparent dead spots on 

 the host are rather remarkable, as they are by no means common 

 in this group of fungi. 



For those who follow Saccardo, this species may be designated 

 as Plasmopara Acalyphae Wilson. 



Kansas Academy of Science, 

 Lawrence, Kansas. 



