Abstract: The new species Pythium hypoandrum Yu & Y. L. Wang exhibits some similarities to P. chamaehyphon Sideris and P. paroecandrum Drcchsler. P. chamaehyphon is distinguished from the new species in having: (1 ) larger oogonia (23--29 pm, av. 26.5 pm in diam.), (2 ) larger oospores (20-27 um, av. 24.3 pm in diam.), (3 ) much large antheridia with more irregular outline, and (4 ) oospores with thinner epispore. On the other hand, P. paroecandrum is different from the new species in having: (1 ) larger antheridia (av. 13.26 x 8.02 um) which are usually sessile, hypogynous and intercalary, (2 ) oogonia which are often in chain and (3 )oospores which are thin-walled (0.8-2.6um, av. 1.59 um in thick-ness).

Key words: Genus Pythium