Achlya fuegiana sp. nov., occurring on litter (floating dead leaves and twi
gs) in Laguna Verde stream, in Tierra del Fuego Province (Argentina) is des
cribed, illustrated and compared with similar species. The species produces
principally papillate oogonia and androgynous antheridial branches. Immatu
re oospheres, oogonial wall and oospores are distinctly yellowish. This Arg
entine species differs from other known ones with centric-subcentric oospor
es in having monoclinous, exiginous, and diclinous branches, a great number
of secondary hyphae near the tips and non-functional antheridial branches.
The oospores are centric-subcentric and 1-3(7) in number, and borne inside
the oogonia.